1
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Greiner J, Dente M, Orós-Rodrigo S, Cameron BA, Madl J, Kaltenbacher W, Kok T, Zgierski-Johnston CM, Peyronnet R, Kohl P, Sacconi L, Rog-Zielinska EA. Different effects of cardiomyocyte contractile activity on transverse and axial tubular system luminal content dynamics. J Mol Cell Cardiol 2024; 197:125-135. [PMID: 39491670 DOI: 10.1016/j.yjmcc.2024.10.014] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/25/2024] [Revised: 10/06/2024] [Accepted: 10/28/2024] [Indexed: 11/05/2024]
Abstract
BACKGROUND Efficient excitation-contraction coupling of mammalian ventricular cardiomyocytes depends on the transverse-axial tubular system (TATS), a network of surface membrane invaginations. TATS enables tight coupling of sarcolemmal and sarcoplasmic reticulum membranes, which is essential for rapid Ca2+-induced Ca2+ release, and uniform contraction upon electrical stimulation. The majority of TATS in healthy ventricular cardiomyocytes is composed of transverse tubules (TT, ∼90 % of TATS in rabbit). The remainder consists of mostly axial tubules (AT), which are less abundant and less well studied. In disease, however, the relative abundance of TT and AT changes. The mechanisms and relevance of this change are not known, and understanding them requires a more targeted effort to study the dynamics of AT structure and function. While TATS content is continuous with the interstitial space, it is contained within a domain of restricted diffusion. We have previously shown that TT are cyclically squeezed during stretch and contraction. This can contribute to TT content mixing and accelerates luminal content exchange with the environment. Here, we explore the effects of cardiomyocyte stretch and contraction on AT. METHODS TATS structure and diffusion dynamics were studied using 3D electron tomography of rabbit left ventricular cardiomyocytes, preserved at rest or during contraction, and ventricular tissue preserved at rest or during stretch, as well as live-cell TATS content exchange measurements. RESULTS We show (i) that cardiomyocyte contraction is associated with an increase in the apparent speed of diffusion of TT content that scales with beating rate and degree of cell shortening. In contrast, (ii) AT develop membrane folds and constrictions during contraction, (iii) with no effect of contraction on luminal exchange dynamics, while (iv) cardiomyocyte stretch is associated with AT straightening and AT and TT 'squeezing' that (v) supports an acceleration of the apparent speed of diffusion in AT and TT. Finally, (vi) we present a simple computational model outlining the potential relevance of AT in healthy and diseased cells. CONCLUSIONS Our results indicate that TT and AT are differently affected by the cardiac contractile cycle, and suggest that AT may play a role in ensuring TATS network content homogeneity in diseased cardiomyocytes. Further research is needed to explore the interplay of structural and functional remodelling of different TATS components in failing myocardium.
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Affiliation(s)
- J Greiner
- Institute for Experimental Cardiovascular Medicine, University Heart Center and Faculty of Medicine, University of Freiburg, Freiburg, Germany; Centre for Integrative Biological Signalling Studies (CIBSS), University of Freiburg, Freiburg, Germany
| | - M Dente
- Department of Experimental and Clinical Medicine, Division of Physiology, University of Florence, Florence, Italy
| | - S Orós-Rodrigo
- Institute for Experimental Cardiovascular Medicine, University Heart Center and Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - B A Cameron
- Institute for Experimental Cardiovascular Medicine, University Heart Center and Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - J Madl
- Institute for Experimental Cardiovascular Medicine, University Heart Center and Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - W Kaltenbacher
- Institute for Experimental Cardiovascular Medicine, University Heart Center and Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - T Kok
- Institute for Experimental Cardiovascular Medicine, University Heart Center and Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - C M Zgierski-Johnston
- Institute for Experimental Cardiovascular Medicine, University Heart Center and Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - R Peyronnet
- Institute for Experimental Cardiovascular Medicine, University Heart Center and Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - P Kohl
- Institute for Experimental Cardiovascular Medicine, University Heart Center and Faculty of Medicine, University of Freiburg, Freiburg, Germany; Centre for Integrative Biological Signalling Studies (CIBSS), University of Freiburg, Freiburg, Germany; Faculty of Engineering, University of Freiburg, Freiburg, Germany
| | - L Sacconi
- Institute for Experimental Cardiovascular Medicine, University Heart Center and Faculty of Medicine, University of Freiburg, Freiburg, Germany; Institute of Clinical Physiology, National Research Council, Florence, Italy
| | - E A Rog-Zielinska
- Institute for Experimental Cardiovascular Medicine, University Heart Center and Faculty of Medicine, University of Freiburg, Freiburg, Germany; Centre for Integrative Biological Signalling Studies (CIBSS), University of Freiburg, Freiburg, Germany.
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2
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Pásek M, Bébarová M, Šimurdová M, Šimurda J. Functional consequences of changes in the distribution of Ca 2+ extrusion pathways between t-tubular and surface membranes in a model of human ventricular cardiomyocyte. J Mol Cell Cardiol 2024; 193:113-124. [PMID: 38960316 DOI: 10.1016/j.yjmcc.2024.06.010] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/18/2023] [Revised: 06/10/2024] [Accepted: 06/29/2024] [Indexed: 07/05/2024]
Abstract
The sarcolemmal Ca2+ efflux pathways, Na+-Ca2+-exchanger (NCX) and Ca2+-ATPase (PMCA), play a crucial role in the regulation of intracellular Ca2+ load and Ca2+ transient in cardiomyocytes. The distribution of these pathways between the t-tubular and surface membrane of ventricular cardiomyocytes varies between species and is not clear in human. Moreover, several studies suggest that this distribution changes during the development and heart diseases. However, the consequences of NCX and PMCA redistribution in human ventricular cardiomyocytes have not yet been elucidated. In this study, we aimed to address this point by using a mathematical model of the human ventricular myocyte incorporating t-tubules, dyadic spaces, and subsarcolemmal spaces. Effects of various combinations of t-tubular fractions of NCX and PMCA were explored, using values between 0.2 and 1 as reported in animal experiments under normal and pathological conditions. Small variations in the action potential duration (≤ 2%), but significant changes in the peak value of cytosolic Ca2+ transient (up to 17%) were observed at stimulation frequencies corresponding to the human heart rate at rest and during activity. The analysis of model results revealed that the changes in Ca2+ transient induced by redistribution of NCX and PMCA were mainly caused by alterations in Ca2+ concentrations in the subsarcolemmal spaces and cytosol during the diastolic phase of the stimulation cycle. The results suggest that redistribution of both transporters between the t-tubular and surface membranes contributes to changes in contractility in human ventricular cardiomyocytes during their development and heart disease and may promote arrhythmogenesis.
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Affiliation(s)
- Michal Pásek
- Institute of Thermomechanics, Czech Academy of Sciences, Prague, Czech Republic; Department of Physiology, Faculty of Medicine, Masaryk University, Brno, Czech Republic.
| | - Markéta Bébarová
- Department of Physiology, Faculty of Medicine, Masaryk University, Brno, Czech Republic; Department of Internal Medicine and Cardiology, University Hospital Brno and Faculty of Medicine, Masaryk University, Brno, Czech Republic
| | - Milena Šimurdová
- Department of Physiology, Faculty of Medicine, Masaryk University, Brno, Czech Republic
| | - Jiří Šimurda
- Department of Physiology, Faculty of Medicine, Masaryk University, Brno, Czech Republic
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3
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Scardigli M, Pásek M, Santini L, Palandri C, Conti E, Crocini C, Campione M, Loew LM, de Vries AAF, Pijnappels DA, Pavone FS, Poggesi C, Cerbai E, Coppini R, Kohl P, Ferrantini C, Sacconi L. Optogenetic confirmation of transverse-tubular membrane excitability in intact cardiac myocytes. J Physiol 2024; 602:791-808. [PMID: 38348881 DOI: 10.1113/jp285202] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2023] [Accepted: 01/17/2024] [Indexed: 03/09/2024] Open
Abstract
T-tubules (TT) form a complex network of sarcolemmal membrane invaginations, essential for well-co-ordinated excitation-contraction coupling (ECC) and thus homogeneous mechanical activation of cardiomyocytes. ECC is initiated by rapid depolarization of the sarcolemmal membrane. Whether TT membrane depolarization is active (local generation of action potentials; AP) or passive (following depolarization of the outer cell surface sarcolemma; SS) has not been experimentally validated in cardiomyocytes. Based on the assessment of ion flux pathways needed for AP generation, we hypothesize that TT are excitable. We therefore explored TT excitability experimentally, using an all-optical approach to stimulate and record trans-membrane potential changes in TT that were structurally disconnected, and hence electrically insulated, from the SS membrane by transient osmotic shock. Our results establish that cardiomyocyte TT can generate AP. These AP show electrical features that differ substantially from those observed in SS, consistent with differences in the density of ion channels and transporters in the two different membrane domains. We propose that TT-generated AP represent a safety mechanism for TT AP propagation and ECC, which may be particularly relevant in pathophysiological settings where morpho-functional changes reduce the electrical connectivity between SS and TT membranes. KEY POINTS: Cardiomyocytes are characterized by a complex network of membrane invaginations (the T-tubular system) that propagate action potentials to the core of the cell, causing uniform excitation-contraction coupling across the cell. In the present study, we investigated whether the T-tubular system is able to generate action potentials autonomously, rather than following depolarization of the outer cell surface sarcolemma. For this purpose, we developed a fully optical platform to probe and manipulate the electrical dynamics of subcellular membrane domains. Our findings demonstrate that T-tubules are intrinsically excitable, revealing distinct characteristics of self-generated T-tubular action potentials. This active electrical capability would protect cells from voltage drops potentially occurring within the T-tubular network.
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Affiliation(s)
- Marina Scardigli
- Department of Experimental and Clinical Medicine, University of Florence, Florence, Italy
| | - Michal Pásek
- Institute of Thermomechanics, Czech Academy of Science, Prague, Czech Republic
- Department of Physiology, Faculty of Medicine, Masaryk University, Brno, Czech Republic
| | - Lorenzo Santini
- Department of Neurology, Psychology, Drug Sciences and Child Health, University of Florence, Florence, Italy
| | - Chiara Palandri
- Department of Neurology, Psychology, Drug Sciences and Child Health, University of Florence, Florence, Italy
| | - Emilia Conti
- European Laboratory for Non-Linear Spectroscopy - LENS, Sesto Fiorentino, Italy
- Neuroscience Institute, National Research Council, Pisa, Italy
| | - Claudia Crocini
- DZHK (German Centre for Cardiovascular Research), Partner Site Berlin, Berlin, Germany
- Max Rubner Center for Cardiovascular Metabolic Renal Research (MRC), Deutsches Herzzentrum der Charité (DHZC), Charité-Universitätsmedizin Berlin, Berlin, Germany
| | - Marina Campione
- Institute of Neuroscience (IN-CNR) and Department of Biomedical Science, University of Padua, Padua, Italy
| | - Leslie M Loew
- Center for Cell Analysis and Modeling, University of Connecticut, Farmington, CT, USA
| | - Antoine A F de Vries
- Laboratory of Experimental Cardiology, Department of Cardiology, Leiden University Medical Center, Leiden, The Netherlands
| | - Daniël A Pijnappels
- Laboratory of Experimental Cardiology, Department of Cardiology, Leiden University Medical Center, Leiden, The Netherlands
| | - Francesco S Pavone
- European Laboratory for Non-Linear Spectroscopy - LENS, Sesto Fiorentino, Italy
| | - Corrado Poggesi
- Department of Experimental and Clinical Medicine, University of Florence, Florence, Italy
| | - Elisabetta Cerbai
- Department of Neurology, Psychology, Drug Sciences and Child Health, University of Florence, Florence, Italy
- European Laboratory for Non-Linear Spectroscopy - LENS, Sesto Fiorentino, Italy
| | - Raffaele Coppini
- Department of Neurology, Psychology, Drug Sciences and Child Health, University of Florence, Florence, Italy
| | - Peter Kohl
- Institute for Experimental Cardiovascular Medicine, University Heart Center and Medical Faculty, University of Freiburg, Freiburg, Germany
| | - Cecilia Ferrantini
- Department of Experimental and Clinical Medicine, University of Florence, Florence, Italy
| | - Leonardo Sacconi
- European Laboratory for Non-Linear Spectroscopy - LENS, Sesto Fiorentino, Italy
- Institute for Experimental Cardiovascular Medicine, University Heart Center and Medical Faculty, University of Freiburg, Freiburg, Germany
- Institute of Clinical Physiology, National Research Council (IFC-CNR), Florence, Italy
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4
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Zhang X, Ni H, Morotti S, Smith C, Sato D, Louch W, Edwards A, Grandi E. Mechanisms of spontaneous Ca 2+ release-mediated arrhythmia in a novel 3D human atrial myocyte model: I. Transverse-axial tubule variation. J Physiol 2023; 601:2655-2683. [PMID: 36094888 PMCID: PMC10008525 DOI: 10.1113/jp283363] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2022] [Accepted: 09/02/2022] [Indexed: 11/08/2022] Open
Abstract
Intracellular calcium (Ca2+ ) cycling is tightly regulated in the healthy heart ensuring effective contraction. This is achieved by transverse (t)-tubule membrane invaginations that facilitate close coupling of key Ca2+ -handling proteins such as the L-type Ca2+ channel and Na+ -Ca2+ exchanger (NCX) on the cell surface with ryanodine receptors (RyRs) on the intracellular Ca2+ store. Although less abundant and regular than in the ventricle, t-tubules also exist in atrial myocytes as a network of transverse invaginations with axial extensions known as the transverse-axial tubule system (TATS). In heart failure and atrial fibrillation, there is TATS remodelling that is associated with aberrant Ca2+ -handling and Ca2+ -induced arrhythmic activity; however, the mechanism underlying this is not fully understood. To address this, we developed a novel 3D human atrial myocyte model that couples electrophysiology and Ca2+ -handling with variable TATS organization and density. We extensively parameterized and validated our model against experimental data to build a robust tool examining TATS regulation of subcellular Ca2+ release. We found that varying TATS density and thus the localization of key Ca2+ -handling proteins has profound effects on Ca2+ handling. Following TATS loss, there is reduced NCX that results in increased cleft Ca2+ concentration through decreased Ca2+ extrusion. This elevated Ca2+ increases RyR open probability causing spontaneous Ca2+ releases and the promotion of arrhythmogenic waves (especially in the cell interior) leading to voltage instabilities through delayed afterdepolarizations. In summary, the present study demonstrates a mechanistic link between TATS remodelling and Ca2+ -driven proarrhythmic behaviour that probably reflects the arrhythmogenic state observed in disease. KEY POINTS: Transverse-axial tubule systems (TATS) modulate Ca2+ handling and excitation-contraction coupling in atrial myocytes, with TATS remodelling in heart failure and atrial fibrillation being associated with altered Ca2+ cycling and subsequent arrhythmogenesis. To investigate the poorly understood mechanisms linking TATS variation and spontaneous Ca2+ release, we built, parameterized and validated a 3D human atrial myocyte model coupling electrophysiology and spatially-detailed subcellular Ca2+ handling governed by the TATS. Simulated TATS loss causes diastolic Ca2+ and voltage instabilities through reduced Na+ -Ca2+ exchanger-mediated Ca2+ removal, cleft Ca2+ accumulation and increased ryanodine receptor open probability, resulting in spontaneous Ca2+ release and promotion of arrhythmogenic waves and delayed afterdepolarizations. At fast electrical rates typical of atrial tachycardia/fibrillation, spontaneous Ca2+ releases are larger and more frequent in the cell interior than at the periphery. Our work provides mechanistic insight into how atrial TATS remodelling can lead to Ca2+ -driven instabilities that may ultimately contribute to the arrhythmogenic state in disease.
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Affiliation(s)
- X. Zhang
- Department of Pharmacology, University of California Davis, Davis, CA, USA
| | - H. Ni
- Department of Pharmacology, University of California Davis, Davis, CA, USA
| | - S. Morotti
- Department of Pharmacology, University of California Davis, Davis, CA, USA
| | - C.E.R. Smith
- Department of Pharmacology, University of California Davis, Davis, CA, USA
| | - D. Sato
- Department of Pharmacology, University of California Davis, Davis, CA, USA
| | - W.E. Louch
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Oslo, Norway
- K.G. Jebsen Centre for Cardiac Research, University of Oslo, Oslo Norway
| | - A.G. Edwards
- Department of Pharmacology, University of California Davis, Davis, CA, USA
- Simula Research Laboratory, Lysaker, Norway
| | - E. Grandi
- Department of Pharmacology, University of California Davis, Davis, CA, USA
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5
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Kohl P, Greiner J, Rog-Zielinska EA. Electron microscopy of cardiac 3D nanodynamics: form, function, future. Nat Rev Cardiol 2022; 19:607-619. [PMID: 35396547 DOI: 10.1038/s41569-022-00677-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 02/04/2022] [Indexed: 11/09/2022]
Abstract
The 3D nanostructure of the heart, its dynamic deformation during cycles of contraction and relaxation, and the effects of this deformation on cell function remain largely uncharted territory. Over the past decade, the first inroads have been made towards 3D reconstruction of heart cells, with a native resolution of around 1 nm3, and of individual molecules relevant to heart function at a near-atomic scale. These advances have provided access to a new generation of data and have driven the development of increasingly smart, artificial intelligence-based, deep-learning image-analysis algorithms. By high-pressure freezing of cardiomyocytes with millisecond accuracy after initiation of an action potential, pseudodynamic snapshots of contraction-induced deformation of intracellular organelles can now be captured. In combination with functional studies, such as fluorescence imaging, exciting insights into cardiac autoregulatory processes at nano-to-micro scales are starting to emerge. In this Review, we discuss the progress in this fascinating new field to highlight the fundamental scientific insight that has emerged, based on technological breakthroughs in biological sample preparation, 3D imaging and data analysis; to illustrate the potential clinical relevance of understanding 3D cardiac nanodynamics; and to predict further progress that we can reasonably expect to see over the next 10 years.
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Affiliation(s)
- Peter Kohl
- Institute for Experimental Cardiovascular Medicine, University Heart Center and Faculty of Medicine, University of Freiburg, Freiburg, Germany.,Faculty of Engineering, University of Freiburg, Freiburg, Germany.,Centre for Integrative Biological Signalling Studies (CIBSS), University of Freiburg, Freiburg, Germany
| | - Joachim Greiner
- Institute for Experimental Cardiovascular Medicine, University Heart Center and Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Eva A Rog-Zielinska
- Institute for Experimental Cardiovascular Medicine, University Heart Center and Faculty of Medicine, University of Freiburg, Freiburg, Germany.
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6
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Abstract
In mammalian cardiac myocytes, the plasma membrane includes the surface sarcolemma but also a network of membrane invaginations called transverse (t-) tubules. These structures carry the action potential deep into the cell interior, allowing efficient triggering of Ca2+ release and initiation of contraction. Once thought to serve as rather static enablers of excitation-contraction coupling, recent work has provided a newfound appreciation of the plasticity of the t-tubule network's structure and function. Indeed, t-tubules are now understood to support dynamic regulation of the heartbeat across a range of timescales, during all stages of life, in both health and disease. This review article aims to summarize these concepts, with consideration given to emerging t-tubule regulators and their targeting in future therapies.
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Affiliation(s)
- Katharine M Dibb
- Unit of Cardiac Physiology, Division of Cardiovascular Sciences, School of Medical Sciences, Faculty of Biology, Medicine and Health, Manchester Academic Health Science Centre, University of Manchester, Manchester, United Kingdom;
| | - William E Louch
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Oslo, Norway
- K.G. Jebsen Centre for Cardiac Research, University of Oslo, Oslo Norway
| | - Andrew W Trafford
- Unit of Cardiac Physiology, Division of Cardiovascular Sciences, School of Medical Sciences, Faculty of Biology, Medicine and Health, Manchester Academic Health Science Centre, University of Manchester, Manchester, United Kingdom;
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7
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Ottolia M, John S, Hazan A, Goldhaber JI. The Cardiac Na + -Ca 2+ Exchanger: From Structure to Function. Compr Physiol 2021; 12:2681-2717. [PMID: 34964124 DOI: 10.1002/cphy.c200031] [Citation(s) in RCA: 24] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Ca2+ homeostasis is essential for cell function and survival. As such, the cytosolic Ca2+ concentration is tightly controlled by a wide number of specialized Ca2+ handling proteins. One among them is the Na+ -Ca2+ exchanger (NCX), a ubiquitous plasma membrane transporter that exploits the electrochemical gradient of Na+ to drive Ca2+ out of the cell, against its concentration gradient. In this critical role, this secondary transporter guides vital physiological processes such as Ca2+ homeostasis, muscle contraction, bone formation, and memory to name a few. Herein, we review the progress made in recent years about the structure of the mammalian NCX and how it relates to function. Particular emphasis will be given to the mammalian cardiac isoform, NCX1.1, due to the extensive studies conducted on this protein. Given the degree of conservation among the eukaryotic exchangers, the information highlighted herein will provide a foundation for our understanding of this transporter family. We will discuss gene structure, alternative splicing, topology, regulatory mechanisms, and NCX's functional role on cardiac physiology. Throughout this article, we will attempt to highlight important milestones in the field and controversial topics where future studies are required. © 2021 American Physiological Society. Compr Physiol 12:1-37, 2021.
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Affiliation(s)
- Michela Ottolia
- Department of Anesthesiology and Perioperative Medicine, Division of Molecular Medicine, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California, USA
| | - Scott John
- Department of Medicine (Cardiology), UCLA, Los Angeles, California, USA
| | - Adina Hazan
- Smidt Heart Institute, Cedars Sinai Medical Center, Los Angeles, California, USA
| | - Joshua I Goldhaber
- Smidt Heart Institute, Cedars Sinai Medical Center, Los Angeles, California, USA
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8
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Petkova MA, Dobrzynski H. Do human sinoatrial node cells have t-tubules? TRANSLATIONAL RESEARCH IN ANATOMY 2021. [DOI: 10.1016/j.tria.2021.100131] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
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9
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Setterberg IE, Le C, Frisk M, Li J, Louch WE. The Physiology and Pathophysiology of T-Tubules in the Heart. Front Physiol 2021; 12:718404. [PMID: 34566684 PMCID: PMC8458775 DOI: 10.3389/fphys.2021.718404] [Citation(s) in RCA: 38] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2021] [Accepted: 07/07/2021] [Indexed: 12/18/2022] Open
Abstract
In cardiomyocytes, invaginations of the sarcolemmal membrane called t-tubules are critically important for triggering contraction by excitation-contraction (EC) coupling. These structures form functional junctions with the sarcoplasmic reticulum (SR), and thereby enable close contact between L-type Ca2+ channels (LTCCs) and Ryanodine Receptors (RyRs). This arrangement in turn ensures efficient triggering of Ca2+ release, and contraction. While new data indicate that t-tubules are capable of exhibiting compensatory remodeling, they are also widely reported to be structurally and functionally compromised during disease, resulting in disrupted Ca2+ homeostasis, impaired systolic and/or diastolic function, and arrhythmogenesis. This review summarizes these findings, while highlighting an emerging appreciation of the distinct roles of t-tubules in the pathophysiology of heart failure with reduced and preserved ejection fraction (HFrEF and HFpEF). In this context, we review current understanding of the processes underlying t-tubule growth, maintenance, and degradation, underscoring the involvement of a variety of regulatory proteins, including junctophilin-2 (JPH2), amphiphysin-2 (BIN1), caveolin-3 (Cav3), and newer candidate proteins. Upstream regulation of t-tubule structure/function by cardiac workload and specifically ventricular wall stress is also discussed, alongside perspectives for novel strategies which may therapeutically target these mechanisms.
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Affiliation(s)
- Ingunn E Setterberg
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Oslo, Norway.,KG Jebsen Centre for Cardiac Research, University of Oslo, Oslo, Norway
| | - Christopher Le
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Oslo, Norway.,KG Jebsen Centre for Cardiac Research, University of Oslo, Oslo, Norway
| | - Michael Frisk
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Oslo, Norway.,KG Jebsen Centre for Cardiac Research, University of Oslo, Oslo, Norway
| | - Jia Li
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Oslo, Norway.,KG Jebsen Centre for Cardiac Research, University of Oslo, Oslo, Norway
| | - William E Louch
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Oslo, Norway.,KG Jebsen Centre for Cardiac Research, University of Oslo, Oslo, Norway
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10
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Pásek M, Šimurda J, Bébarová M, Christé G. Divergent estimates of the ratio between Na+-Ca2+ current densities in t-tubular and surface membranes of rat ventricular cardiomyocytes. J Cell Sci 2021; 134:jcs258228. [PMID: 34313306 DOI: 10.1242/jcs.258228] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2020] [Accepted: 05/24/2021] [Indexed: 11/20/2022] Open
Abstract
The ratio between Na+-Ca2+ exchange current densities in t-tubular and surface membranes of rat ventricular cardiomyocytes (JNaCa-ratio) estimated from electrophysiological data published to date yields strikingly different values between 1.7 and nearly 40. Possible reasons for such divergence were analysed by Monte Carlo simulations assuming both normal and log-normal distribution of the measured data. The confidence intervals CI95 of the mean JNaCa-ratios computed from the reported data showed an overlap of values between 1 and 3, and between 0.3 and 4.3 in the case of normal and log-normal distribution, respectively. Further analyses revealed that the published high values likely result from a large scatter of data due to transmural differences in JNaCa, dispersion of cell membrane capacitances and variability in incomplete detubulation. Taking into account the asymmetric distribution of the measured data, the reduction of mean current densities after detubulation and the substantially smaller CI95 of lower values of the mean JNaCa-ratio, the values between 1.6 and 3.2 may be considered as the most accurate estimates. This implies that 40 to 60% of Na+-Ca2+ exchanger is located at the t-tubular membrane of adult rat ventricular cardiomyocytes.
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Affiliation(s)
- Michal Pásek
- Institute of Thermomechanics, Czech Academy of Science, Dolejškova 5, 182 00, Prague, Czech Republic
- Department of Physiology, Faculty of Medicine, Masaryk University, Kamenice 5, 625 00, Brno, Czech Republic
| | - Jiří Šimurda
- Department of Physiology, Faculty of Medicine, Masaryk University, Kamenice 5, 625 00, Brno, Czech Republic
| | - Markéta Bébarová
- Department of Physiology, Faculty of Medicine, Masaryk University, Kamenice 5, 625 00, Brno, Czech Republic
| | - Georges Christé
- Laboratoire de Neurocardiologie, EA4612, Université Lyon 1, Lyon F-69003, France
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11
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Mellor NG, Pham T, Tran K, Loiselle DS, Ward M, Taberner AJ, Crossman DJ, Han J. Disruption of transverse-tubular network reduces energy efficiency in cardiac muscle contraction. Acta Physiol (Oxf) 2021; 231:e13545. [PMID: 32757472 DOI: 10.1111/apha.13545] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2020] [Revised: 07/16/2020] [Accepted: 07/31/2020] [Indexed: 11/29/2022]
Abstract
AIM Altered organization of the transverse-tubular network is an early pathological event occurring even prior to the onset of heart failure. Such t-tubular remodelling disturbs the synchrony and signalling between membranous and intracellular ion channels, exchangers, receptors and ATPases essential in the dynamics of excitation-contraction coupling, leading to ionic abnormality and mechanical dysfunction in heart disease progression. In this study, we investigated whether a disrupted t-tubular network has a direct effect on cardiac mechano-energetics. Our aim was to understand the fundamental link between t-tubular remodelling and impaired energy metabolism, both of which are characteristics of heart failure. We thus studied healthy tissue preparations in which cellular processes are not altered by any disease event. METHODS We exploited the "formamide-detubulation" technique to acutely disrupt the t-tubular network in rat left-ventricular trabeculae. We assessed the energy utilization by cellular Ca2+ cycling and by crossbridge cycling, and quantified the change of energy efficiency following detubulation. For these measurements, trabeculae were mounted in a microcalorimeter where force and heat output were simultaneously measured. RESULTS Following structural disorganization from detubulation, muscle heat output associated with Ca2+ cycling was reduced, indicating impaired intracellular Ca2+ homeostasis. This led to reduced force production and heat output by crossbridge cycling. The reduction in force-length work was not paralleled by proportionate reduction in the heat output and, as such, energy efficiency was reduced. CONCLUSIONS These results reveal the direct energetic consequences of disrupted t-tubular network, linking the energy disturbance and the t-tubular remodelling typically observed in heart failure.
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Affiliation(s)
- Nicholas G. Mellor
- Auckland Bioengineering Institute The University of Auckland Auckland New Zealand
| | - Toan Pham
- Auckland Bioengineering Institute The University of Auckland Auckland New Zealand
| | - Kenneth Tran
- Auckland Bioengineering Institute The University of Auckland Auckland New Zealand
| | - Denis S. Loiselle
- Auckland Bioengineering Institute The University of Auckland Auckland New Zealand
- Department of Physiology The University of Auckland Auckland New Zealand
| | - Marie‐Louise Ward
- Department of Physiology The University of Auckland Auckland New Zealand
| | - Andrew J. Taberner
- Auckland Bioengineering Institute The University of Auckland Auckland New Zealand
- Department of Engineering Science The University of Auckland Auckland New Zealand
| | - David J. Crossman
- Department of Physiology The University of Auckland Auckland New Zealand
| | - June‐Chiew Han
- Auckland Bioengineering Institute The University of Auckland Auckland New Zealand
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12
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Rog-Zielinska EA, Scardigli M, Peyronnet R, Zgierski-Johnston CM, Greiner J, Madl J, O'Toole ET, Morphew M, Hoenger A, Sacconi L, Kohl P. Beat-by-Beat Cardiomyocyte T-Tubule Deformation Drives Tubular Content Exchange. Circ Res 2020; 128:203-215. [PMID: 33228470 PMCID: PMC7834912 DOI: 10.1161/circresaha.120.317266] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Supplemental Digital Content is available in the text. The sarcolemma of cardiomyocytes contains many proteins that are essential for electromechanical function in general, and excitation-contraction coupling in particular. The distribution of these proteins is nonuniform between the bulk sarcolemmal surface and membrane invaginations known as transverse tubules (TT). TT form an intricate network of fluid-filled conduits that support electromechanical synchronicity within cardiomyocytes. Although continuous with the extracellular space, the narrow lumen and the tortuous structure of TT can form domains of restricted diffusion. As a result of unequal ion fluxes across cell surface and TT membranes, limited diffusion may generate ion gradients within TT, especially deep within the TT network and at high pacing rates.
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Affiliation(s)
- Eva A Rog-Zielinska
- Institute for Experimental Cardiovascular Medicine, University Heart Center Freiburg-Bad Krozingen, and Faculty of Medicine, University of Freiburg, Germany (E.A.R.-Z., R.P., C.M.Z.-J., J.G., J.M., L.S., P.K.)
| | - Marina Scardigli
- European Laboratory for Non-Linear Spectroscopy, National Institute of Optics, National Research Council, Sesto Fiorentino (Florence), Italy (M.S., L.S.)
| | - Remi Peyronnet
- Institute for Experimental Cardiovascular Medicine, University Heart Center Freiburg-Bad Krozingen, and Faculty of Medicine, University of Freiburg, Germany (E.A.R.-Z., R.P., C.M.Z.-J., J.G., J.M., L.S., P.K.)
| | - Callum M Zgierski-Johnston
- Institute for Experimental Cardiovascular Medicine, University Heart Center Freiburg-Bad Krozingen, and Faculty of Medicine, University of Freiburg, Germany (E.A.R.-Z., R.P., C.M.Z.-J., J.G., J.M., L.S., P.K.)
| | - Joachim Greiner
- Institute for Experimental Cardiovascular Medicine, University Heart Center Freiburg-Bad Krozingen, and Faculty of Medicine, University of Freiburg, Germany (E.A.R.-Z., R.P., C.M.Z.-J., J.G., J.M., L.S., P.K.)
| | - Josef Madl
- Institute for Experimental Cardiovascular Medicine, University Heart Center Freiburg-Bad Krozingen, and Faculty of Medicine, University of Freiburg, Germany (E.A.R.-Z., R.P., C.M.Z.-J., J.G., J.M., L.S., P.K.)
| | - Eileen T O'Toole
- Department of Molecular, Cellular and Developmental Biology, University of Colorado at Boulder (E.T.O., M.M., A.H.)
| | - Mary Morphew
- Department of Molecular, Cellular and Developmental Biology, University of Colorado at Boulder (E.T.O., M.M., A.H.)
| | - Andreas Hoenger
- Department of Molecular, Cellular and Developmental Biology, University of Colorado at Boulder (E.T.O., M.M., A.H.)
| | - Leonardo Sacconi
- Institute for Experimental Cardiovascular Medicine, University Heart Center Freiburg-Bad Krozingen, and Faculty of Medicine, University of Freiburg, Germany (E.A.R.-Z., R.P., C.M.Z.-J., J.G., J.M., L.S., P.K.).,European Laboratory for Non-Linear Spectroscopy, National Institute of Optics, National Research Council, Sesto Fiorentino (Florence), Italy (M.S., L.S.)
| | - Peter Kohl
- Institute for Experimental Cardiovascular Medicine, University Heart Center Freiburg-Bad Krozingen, and Faculty of Medicine, University of Freiburg, Germany (E.A.R.-Z., R.P., C.M.Z.-J., J.G., J.M., L.S., P.K.).,CIBSS Centre for Integrative Biological Signalling Studies, University of Freiburg, Germany (P.K.)
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13
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Christé G, Bonvallet R, Chouabe C. Accounting for cardiac t-tubule increase with age and myocyte volume to improve measurements of its membrane area and ionic current densities. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2020; 157:40-53. [DOI: 10.1016/j.pbiomolbio.2020.06.005] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/01/2019] [Revised: 06/14/2020] [Accepted: 06/17/2020] [Indexed: 02/02/2023]
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14
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Skogestad J, Aronsen JM, Tovsrud N, Wanichawan P, Hougen K, Stokke MK, Carlson CR, Sjaastad I, Sejersted OM, Swift F. Coupling of the Na+/K+-ATPase to Ankyrin B controls Na+/Ca2+ exchanger activity in cardiomyocytes. Cardiovasc Res 2020; 116:78-90. [PMID: 30949686 DOI: 10.1093/cvr/cvz087] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/27/2018] [Revised: 02/22/2019] [Accepted: 04/03/2019] [Indexed: 01/28/2023] Open
Abstract
AIMS Ankyrin B (AnkB) is an adaptor protein that assembles Na+/K+-ATPase (NKA) and Na+/Ca2+ exchanger (NCX) in the AnkB macromolecular complex. Loss-of-function mutations in AnkB cause the AnkB syndrome in humans, characterized by ventricular arrhythmias and sudden cardiac death. It is unclear to what extent NKA binding to AnkB allows regulation of local Na+ and Ca2+ domains and hence NCX activity. METHODS AND RESULTS To investigate the role of NKA binding to AnkB in cardiomyocytes, we synthesized a disruptor peptide (MAB peptide) and its AnkB binding ability was verified by pulldown experiments. As opposed to control, the correlation between NKA and NCX currents was abolished in adult rat ventricular myocytes dialyzed with MAB peptide, as well as in cardiomyocytes from AnkB+/- mice. Disruption of NKA from AnkB (with MAB peptide) increased NCX-sensed cytosolic Na+ concentration, reduced Ca2+ extrusion through NCX, and increased frequency of Ca2+ sparks and Ca2+ waves without concomitant increase in Ca2+ transient amplitude or SR Ca2+ load, suggesting an effect in local Ca2+ domains. Selective inhibition of the NKAα2 isoform abolished both the correlation between NKA and NCX currents and the increased rate of Ca2+ sparks and waves following NKA/AnkB disruption, suggesting that an AnkB/NKAα2/NCX domain controls Ca2+ fluxes in cardiomyocytes. CONCLUSION NKA binding to AnkB allows ion regulation in a local domain, and acute disruption of the NKA/AnkB interaction using disruptor peptides lead to increased rate of Ca2+ sparks and waves. The functional effects were mediated through the NKAα2 isoform. Disruption of the AnkB/NKA/NCX domain could be an important pathophysiological mechanism in the AnkB syndrome.
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Affiliation(s)
- Jonas Skogestad
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Ullevål, N-0407 Oslo, Norway.,KG Jebsen Cardiac Research Centre and Center for Heart Failure Research, University of Oslo, Oslo, Norway
| | - Jan Magnus Aronsen
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Ullevål, N-0407 Oslo, Norway.,Bjørknes College, Oslo, Norway
| | - Nils Tovsrud
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Ullevål, N-0407 Oslo, Norway.,KG Jebsen Cardiac Research Centre and Center for Heart Failure Research, University of Oslo, Oslo, Norway
| | - Pimthanya Wanichawan
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Ullevål, N-0407 Oslo, Norway.,KG Jebsen Cardiac Research Centre and Center for Heart Failure Research, University of Oslo, Oslo, Norway
| | - Karina Hougen
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Ullevål, N-0407 Oslo, Norway.,KG Jebsen Cardiac Research Centre and Center for Heart Failure Research, University of Oslo, Oslo, Norway
| | - Mathis Korseberg Stokke
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Ullevål, N-0407 Oslo, Norway.,KG Jebsen Cardiac Research Centre and Center for Heart Failure Research, University of Oslo, Oslo, Norway.,Department of Cardiology, Oslo University Hospital, Rikshospitalet, Oslo, Norway
| | - Cathrine Rein Carlson
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Ullevål, N-0407 Oslo, Norway.,KG Jebsen Cardiac Research Centre and Center for Heart Failure Research, University of Oslo, Oslo, Norway
| | - Ivar Sjaastad
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Ullevål, N-0407 Oslo, Norway.,KG Jebsen Cardiac Research Centre and Center for Heart Failure Research, University of Oslo, Oslo, Norway
| | - Ole Mathias Sejersted
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Ullevål, N-0407 Oslo, Norway.,KG Jebsen Cardiac Research Centre and Center for Heart Failure Research, University of Oslo, Oslo, Norway
| | - Fredrik Swift
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Ullevål, N-0407 Oslo, Norway.,KG Jebsen Cardiac Research Centre and Center for Heart Failure Research, University of Oslo, Oslo, Norway.,Centre for Fertility and Health, Norwegian Institute of Public Health, Oslo, Norway
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15
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Power A, Kaur S, Dyer C, Ward ML. Disruption of Transverse-Tubules Eliminates the Slow Force Response to Stretch in Isolated Rat Trabeculae. Front Physiol 2020; 11:193. [PMID: 32210837 PMCID: PMC7069251 DOI: 10.3389/fphys.2020.00193] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2019] [Accepted: 02/19/2020] [Indexed: 12/15/2022] Open
Abstract
Ventricular muscle has a biphasic response to stretch. There is an immediate increase in force that coincides with the stretch which is followed by a second phase that takes several minutes for force to develop to a new steady state. The initial increase in force is due to changes in myofilament properties, whereas the second, slower component of the stretch response (known as the “slow force response” or SFR) is accompanied by a steady increase in Ca2+ transient amplitude. Evidence shows stretch-dependent Ca2+ influx during the SFR occurs through some mechanism that is continuously active for several minutes following stretch. Many of the candidate ion channels are located primarily in the t-tubules, which are consequently lost in heart disease. Our aim, therefore, was to investigate the impact of t-tubule loss on the SFR in non-failing cardiac trabeculae in which expression of the different Ca2+ handling proteins was not altered by any disease process. For comparison, we also investigated the effect of formamide detubulation of trabeculae on β-adrenergic activation (1 μM isoproterenol), since this is another key regulator of cardiac force. Measurement of intracellular calcium ([Ca2+]i) and isometric stress were made in RV trabeculae from rat hearts before, during and after formamide treatment (1.5 M for 5 min), which on washout seals the surface sarcolemmal t-tubule openings. Results showed detubulation slowed the time course of Ca2+ transients and twitch force, with time-to-peak, maximum rate-of-rise, and relaxation prolonged in trabeculae at optimal length (Lo). Formamide treatment also prevented development of the SFR following a step change in length from 90 to 100% Lo, and blunted the response to β-adrenergic activation (1 μM isoproterenol).
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Affiliation(s)
- Amelia Power
- Department of Physiology, Faculty of Medical and Health Sciences, University of Auckland, New Zealand
| | - Sarbjot Kaur
- Department of Physiology, Faculty of Medical and Health Sciences, University of Auckland, New Zealand
| | - Cameron Dyer
- Department of Physiology, Faculty of Medical and Health Sciences, University of Auckland, New Zealand
| | - Marie-Louise Ward
- Department of Physiology, Faculty of Medical and Health Sciences, University of Auckland, New Zealand
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16
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Abu-Khousa M, Fiegle DJ, Sommer ST, Minabari G, Milting H, Heim C, Weyand M, Tomasi R, Dendorfer A, Volk T, Seidel T. The Degree of t-System Remodeling Predicts Negative Force-Frequency Relationship and Prolonged Relaxation Time in Failing Human Myocardium. Front Physiol 2020; 11:182. [PMID: 32231589 PMCID: PMC7083140 DOI: 10.3389/fphys.2020.00182] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2019] [Accepted: 02/17/2020] [Indexed: 01/28/2023] Open
Abstract
The normally positive cardiac force-frequency relationship (FFR) becomes flat or negative in chronic heart failure (HF). Here we explored if remodeling of the cardiomyocyte transverse tubular system (t-system) is associated with alterations in FFR and contractile kinetics in failing human myocardium. Left-ventricular myocardial slices from 13 failing human hearts were mounted into a biomimetic culture setup. Maximum twitch force (F), 90% contraction duration (CD90), time to peak force (TTP) and time to relaxation (TTR) were determined at 37°C and 0.2–2 Hz pacing frequency. F1Hz/F0.5Hz and F2Hz/F0.5Hz served as measures of FFR, intracellular cardiomyocyte t-tubule distance (ΔTT) as measure of t-system remodeling. Protein levels of SERCA2, NCX1, and PLB were quantified by immunoblotting. F1Hz/F0.5Hz (R2 = 0.82) and F2Hz/F0.5Hz (R2 = 0.5) correlated negatively with ΔTT, i.e., samples with severe t-system loss exhibited a negative FFR and reduced myocardial wall tension at high pacing rates. PLB levels also predicted F1Hz/F0.5Hz, but to a lesser degree (R2 = 0.49), whereas NCX1 was not correlated (R2 = 0.02). CD90 correlated positively with ΔTT (R2 = 0.39) and negatively with SERCA2/PLB (R2 = 0.42), indicating that both the t-system and SERCA activity are important for contraction kinetics. Surprisingly, ΔTT was not associated with TTP (R2 = 0) but rather with TTR (R2 = 0.5). This became even more pronounced when interaction with NCX1 expression was added to the model (R2 = 0.79), suggesting that t-system loss impairs myocardial relaxation especially when NCX1 expression is low. The degree of t-system remodeling predicts FFR inversion and contraction slowing in failing human myocardium. Moreover, together with NCX, the t-system may be important for myocardial relaxation.
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Affiliation(s)
- Maha Abu-Khousa
- Institute of Cellular and Molecular Physiology, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany
| | - Dominik J Fiegle
- Institute of Cellular and Molecular Physiology, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany
| | - Sophie T Sommer
- Institute of Cellular and Molecular Physiology, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany
| | - Ghazali Minabari
- Department of Cardiac Surgery, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany
| | - Hendrik Milting
- Erich and Hanna Klessmann Institute, Clinic for Thoracic and Cardiovascular Surgery, Heart and Diabetes Center NRW, Ruhr University Bochum, Bad Oeynhausen, Germany
| | - Christian Heim
- Department of Cardiac Surgery, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany
| | - Michael Weyand
- Department of Cardiac Surgery, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany.,Muscle Research Center Erlangen (MURCE), Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany
| | - Roland Tomasi
- Walter Brendel Centre of Experimental Medicine, University Hospital, LMU Munich, Munich, Germany.,Department of Anaesthesiology, University Hospital, LMU Munich, Munich, Germany
| | - Andreas Dendorfer
- Walter Brendel Centre of Experimental Medicine, University Hospital, LMU Munich, Munich, Germany.,German Center for Cardiovascular Research (DZHK), Partner Site Munich Heart Alliance, Munich, Germany
| | - Tilmann Volk
- Institute of Cellular and Molecular Physiology, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany.,Muscle Research Center Erlangen (MURCE), Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany
| | - Thomas Seidel
- Institute of Cellular and Molecular Physiology, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany.,Muscle Research Center Erlangen (MURCE), Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany
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17
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Tazmini K, Frisk M, Lewalle A, Laasmaa M, Morotti S, Lipsett DB, Manfra O, Skogestad J, Aronsen JM, Sejersted OM, Sjaastad I, Edwards AG, Grandi E, Niederer SA, Øie E, Louch WE. Hypokalemia Promotes Arrhythmia by Distinct Mechanisms in Atrial and Ventricular Myocytes. Circ Res 2020; 126:889-906. [PMID: 32070187 PMCID: PMC7098435 DOI: 10.1161/circresaha.119.315641] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
RATIONALE Hypokalemia occurs in up to 20% of hospitalized patients and is associated with increased incidence of ventricular and atrial fibrillation. It is unclear whether these differing types of arrhythmia result from direct and perhaps distinct effects of hypokalemia on cardiomyocytes. OBJECTIVE To investigate proarrhythmic mechanisms of hypokalemia in ventricular and atrial myocytes. METHODS AND RESULTS Experiments were performed in isolated rat myocytes exposed to simulated hypokalemia conditions (reduction of extracellular [K+] from 5.0 to 2.7 mmol/L) and supported by mathematical modeling studies. Ventricular cells subjected to hypokalemia exhibited Ca2+ overload and increased generation of both spontaneous Ca2+ waves and delayed afterdepolarizations. However, similar Ca2+-dependent spontaneous activity during hypokalemia was only observed in a minority of atrial cells that were observed to contain t-tubules. This effect was attributed to close functional pairing of the Na+-K+ ATPase and Na+-Ca2+ exchanger proteins within these structures, as reduction in Na+ pump activity locally inhibited Ca2+ extrusion. Ventricular myocytes and tubulated atrial myocytes additionally exhibited early afterdepolarizations during hypokalemia, associated with Ca2+ overload. However, early afterdepolarizations also occurred in untubulated atrial cells, despite Ca2+ quiescence. These phase-3 early afterdepolarizations were rather linked to reactivation of nonequilibrium Na+ current, as they were rapidly blocked by tetrodotoxin. Na+ current-driven early afterdepolarizations in untubulated atrial cells were enabled by membrane hyperpolarization during hypokalemia and short action potential configurations. Brief action potentials were in turn maintained by ultra-rapid K+ current (IKur); a current which was found to be absent in tubulated atrial myocytes and ventricular myocytes. CONCLUSIONS Distinct mechanisms underlie hypokalemia-induced arrhythmia in the ventricle and atrium but also vary between atrial myocytes depending on subcellular structure and electrophysiology.
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Affiliation(s)
- Kiarash Tazmini
- From the Institute for Experimental Medical Research, Oslo University Hospital (K.T., M.F., M.L., D.B.L., O.M., J.S., J.M.A., O.M.S., I.S., W.E.L.), University of Oslo, Norway
- Department of Internal Medicine, Diakonhjemmet Hospital, Oslo, Norway (K.T., E.Ø.)
| | - Michael Frisk
- From the Institute for Experimental Medical Research, Oslo University Hospital (K.T., M.F., M.L., D.B.L., O.M., J.S., J.M.A., O.M.S., I.S., W.E.L.), University of Oslo, Norway
- KG Jebsen Center for Cardiac Research (M.F., M.L., O.M., I.S., W.E.L.), University of Oslo, Norway
| | - Alexandre Lewalle
- Division of Imaging Sciences and Biomedical Engineering, King’s College London, United Kingdom (A.L., S.A.N.)
| | - Martin Laasmaa
- From the Institute for Experimental Medical Research, Oslo University Hospital (K.T., M.F., M.L., D.B.L., O.M., J.S., J.M.A., O.M.S., I.S., W.E.L.), University of Oslo, Norway
- KG Jebsen Center for Cardiac Research (M.F., M.L., O.M., I.S., W.E.L.), University of Oslo, Norway
| | - Stefano Morotti
- Department of Pharmacology, School of Medicine, University of California Davis (S.M., A.G.E., E.G.)
| | - David B. Lipsett
- From the Institute for Experimental Medical Research, Oslo University Hospital (K.T., M.F., M.L., D.B.L., O.M., J.S., J.M.A., O.M.S., I.S., W.E.L.), University of Oslo, Norway
| | - Ornella Manfra
- From the Institute for Experimental Medical Research, Oslo University Hospital (K.T., M.F., M.L., D.B.L., O.M., J.S., J.M.A., O.M.S., I.S., W.E.L.), University of Oslo, Norway
- KG Jebsen Center for Cardiac Research (M.F., M.L., O.M., I.S., W.E.L.), University of Oslo, Norway
| | - Jonas Skogestad
- From the Institute for Experimental Medical Research, Oslo University Hospital (K.T., M.F., M.L., D.B.L., O.M., J.S., J.M.A., O.M.S., I.S., W.E.L.), University of Oslo, Norway
| | - Jan M. Aronsen
- From the Institute for Experimental Medical Research, Oslo University Hospital (K.T., M.F., M.L., D.B.L., O.M., J.S., J.M.A., O.M.S., I.S., W.E.L.), University of Oslo, Norway
- Bjørknes College, Oslo, Norway (J.M.A.)
| | - Ole M. Sejersted
- From the Institute for Experimental Medical Research, Oslo University Hospital (K.T., M.F., M.L., D.B.L., O.M., J.S., J.M.A., O.M.S., I.S., W.E.L.), University of Oslo, Norway
| | - Ivar Sjaastad
- From the Institute for Experimental Medical Research, Oslo University Hospital (K.T., M.F., M.L., D.B.L., O.M., J.S., J.M.A., O.M.S., I.S., W.E.L.), University of Oslo, Norway
- KG Jebsen Center for Cardiac Research (M.F., M.L., O.M., I.S., W.E.L.), University of Oslo, Norway
| | - Andrew G. Edwards
- Department of Pharmacology, School of Medicine, University of California Davis (S.M., A.G.E., E.G.)
| | - Eleonora Grandi
- Department of Pharmacology, School of Medicine, University of California Davis (S.M., A.G.E., E.G.)
| | - Steven A. Niederer
- Division of Imaging Sciences and Biomedical Engineering, King’s College London, United Kingdom (A.L., S.A.N.)
| | - Erik Øie
- Department of Internal Medicine, Diakonhjemmet Hospital, Oslo, Norway (K.T., E.Ø.)
| | - William E. Louch
- From the Institute for Experimental Medical Research, Oslo University Hospital (K.T., M.F., M.L., D.B.L., O.M., J.S., J.M.A., O.M.S., I.S., W.E.L.), University of Oslo, Norway
- KG Jebsen Center for Cardiac Research (M.F., M.L., O.M., I.S., W.E.L.), University of Oslo, Norway
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18
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Nader M. The SLMAP/Striatin complex: An emerging regulator of normal and abnormal cardiac excitation-contraction coupling. Eur J Pharmacol 2019; 858:172491. [PMID: 31233748 DOI: 10.1016/j.ejphar.2019.172491] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2019] [Revised: 06/19/2019] [Accepted: 06/20/2019] [Indexed: 12/01/2022]
Abstract
The excitation-contraction (E-C) module involves a harmonized correspondence between the sarcolemma and the sarcoplasmic reticulum. This is provided by membrane proteins, which primarily shape the caveolae, the T-tubule/Sarcoplasmic reticulum (TT/SR) junction, and the intercalated discs (ICDs). Distortion of either one of these structures impairs myocardial contraction, and subsequently translates into cardiac failure. Thus, detailed studies on the molecular cues of the E-C module are becoming increasingly necessary to pharmacologically eradicate cardiac failure Herein we reviewed the organization of caveolae, TT/SR junctions, and the ICDs in the heart, with special attention to the Sarcolemma Membrane Associated Protein (SLMAP) and striatin (STRN) in cardiac membranes biology and cardiomyocyte contraction. We emphasized on their in vivo and in vitro signaling in cardiac function/dysfunction. SLMAP is a cardiac membrane protein that plays an important role in E-C coupling and the adrenergic response of the heart. Similarly, STRN is a dynamic protein that is also involved in cardiac E-C coupling and ICD-related cardiomyopathies. Both SLMAP and STRN are linked to cardiac conditions, including heart failure, and their role in cardiomyocyte function was elucidated in our laboratory. They interact together in a protein complex that holds therapeutic potentials for cardiac dysfunction. This review is the first of its kind to conceptualize the role of the SLMAP/STRN complex in cardiac function and failure. It provides in depth information on the signaling of these two proteins and projects their interaction as a novel therapeutic target for cardiac failure.
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Affiliation(s)
- Moni Nader
- Department of Physiological Sciences, College of Medicine, Alfaisal University, Riyadh, 11533, P.O. Box 50927, Saudi Arabia; Department of Genetics, King Faisal Specialist Hospital and Research Center, Riyadh, Saudi Arabia.
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19
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An expanded proteome of cardiac t-tubules. Cardiovasc Pathol 2019; 42:15-20. [PMID: 31202980 DOI: 10.1016/j.carpath.2019.05.001] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/27/2019] [Revised: 04/29/2019] [Accepted: 05/17/2019] [Indexed: 01/04/2023] Open
Abstract
BACKGROUND Transverse tubules (t-tubules) are important structural elements, derived from sarcolemma, found on all striated myocytes. These specialized organelles create a scaffold for many proteins crucial to the effective propagation of signal in cardiac excitation-contraction coupling. The full protein composition of this region is unknown. METHODS We characterized the t-tubule subproteome using 52,033 immunohistochemical images covering 13,203 proteins from the Human Protein Atlas (HPA) cardiac tissue microarrays. We used HPASubC, a suite of Python tools, to rapidly review and classify each image for a specific t-tubule staining pattern. The tools Gene Cards, String 11, and Gene Ontology Consortium as well as literature searches were used to understand pathways and relationships between the proteins. RESULTS There were 96 likely t-tubule proteins identified by HPASubC. Of these, 12 were matrisome proteins and 3 were mitochondrial proteins. A separate literature search identified 50 known t-tubule proteins. A comparison of the 2 lists revealed only 17 proteins in common, including 8 of the matrisome proteins. String11 revealed that 94 of 127 combined t-tubule proteins generated a single interconnected network. CONCLUSION Using HPASubC and the HPA, we identified 78 novel, putative t-tubule proteins and validated 17 within the literature. This expands and improves our knowledge of this important subcellular structure of the cardiac myocyte. This information can be used to identify new structural targets involved in excitation-contraction coupling that may be altered in disease.
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20
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Affiliation(s)
- Stuart G Campbell
- From the Department of Biomedical Engineering (S.G.C.), Yale University, New Haven, CT.,Department of Cellular and Molecular Physiology (S.G.C.), Yale School of Medicine, New Haven, CT
| | - Yibing Qyang
- From the Department of Biomedical Engineering (S.G.C.), Yale University, New Haven, CT.,Yale Stem Cell Center (Y.Q.), Yale University, New Haven, CT.,Vascular Biology and Therapeutics Program (Y.Q.), Yale University, New Haven, CT.,Yale Cardiovascular Research Center, Section of Cardiovascular Medicine, Department of Internal Medicine (Y.Q.), Yale School of Medicine, New Haven, CT
| | - J Travis Hinson
- The Jackson Laboratory for Genomic Medicine, Farmington, CT (J.T.H.).,Department of Cardiology, UConn Health, Farmington, CT (J.T.H.)
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Chu L, Greenstein JL, Winslow RL. Na + microdomains and sparks: Role in cardiac excitation-contraction coupling and arrhythmias in ankyrin-B deficiency. J Mol Cell Cardiol 2019; 128:145-157. [PMID: 30731085 DOI: 10.1016/j.yjmcc.2019.02.001] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/06/2018] [Revised: 02/01/2019] [Accepted: 02/02/2019] [Indexed: 01/25/2023]
Abstract
Cardiac sodium (Na+) potassium ATPase (NaK) pumps, neuronal sodium channels (INa), and sodium calcium (Ca2+) exchangers (NCX1) may co-localize to form a Na+ microdomain. It remains controversial as to whether neuronal INa contributes to local Na+ accumulation, resulting in reversal of nearby NCX1 and influx of Ca2+ into the cell. Therefore, there has been great interest in the possible roles of a Na+ microdomain in cardiac Ca2+-induced Ca2+ release (CICR). In addition, the important role of co-localization of NaK and NCX1 in regulating localized Na+ and Ca2+ levels and CICR in ankyrin-B deficient (ankyrin-B+/-) cardiomyocytes has been examined in many recent studies. Altered Na+ dynamics may contribute to the appearance of arrhythmias, but the mechanisms underlying this relationship remain unclear. In order to investigate this, we present a mechanistic canine cardiomyocyte model which reproduces independent local dyadic junctional SR (JSR) Ca2+ release events underlying cell-wide excitation-contraction coupling, as well as a three-dimensional super-resolution model of the Ca2+ spark that describes local Na+ dynamics as governed by NaK pumps, neuronal INa, and NCX1. The model predicts the existence of Na+ sparks, which are generated by NCX1 and exhibit significantly slower dynamics as compared to Ca2+ sparks. Moreover, whole-cell simulations indicate that neuronal INa in the cardiac dyad plays a key role during the systolic phase. Rapid inward neuronal INa can elevate dyadic [Na+] to 35-40 mM, which drives reverse-mode NCX1 transport, and therefore promotes Ca2+ entry into the dyad, enhancing the trigger for JSR Ca2+ release. The specific role of decreased co-localization of NaK and NCX1 in ankyrin-B+/- cardiomyocytes was examined. Model results demonstrate that a reduction in the local NCX1- and NaK-mediated regulation of dyadic [Ca2+] and [Na+] results in an increase in Ca2+ spark activity during isoproterenol stimulation, which in turn stochastically activates NCX1 in the dyad. This alteration in NCX1/NaK co-localization interrupts the balance between NCX1 and NaK currents in a way that leads to enhanced depolarizing inward current during the action potential plateau, which ultimately leads to a higher probability of L-type Ca2+ channel reopening and arrhythmogenic early-afterdepolarizations.
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Affiliation(s)
- Lulu Chu
- Department of Biomedical Engineering and the Institute for Computational Medicine, The Johns Hopkins University School of Medicine and Whiting School of Engineering, 3400 N Charles Street, Baltimore, MD 21218, USA.
| | - Joseph L Greenstein
- Department of Biomedical Engineering and the Institute for Computational Medicine, The Johns Hopkins University School of Medicine and Whiting School of Engineering, 3400 N Charles Street, Baltimore, MD 21218, USA.
| | - Raimond L Winslow
- Department of Biomedical Engineering and the Institute for Computational Medicine, The Johns Hopkins University School of Medicine and Whiting School of Engineering, 3400 N Charles Street, Baltimore, MD 21218, USA.
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22
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Røe ÅT, Aronsen JM, Skårdal K, Hamdani N, Linke WA, Danielsen HE, Sejersted OM, Sjaastad I, Louch WE. Increased passive stiffness promotes diastolic dysfunction despite improved Ca2+ handling during left ventricular concentric hypertrophy. Cardiovasc Res 2018; 113:1161-1172. [PMID: 28472418 PMCID: PMC5852536 DOI: 10.1093/cvr/cvx087] [Citation(s) in RCA: 55] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/13/2016] [Accepted: 05/03/2017] [Indexed: 02/06/2023] Open
Abstract
Aims Concentric hypertrophy following pressure-overload is linked to preserved systolic function but impaired diastolic function, and is an important substrate for heart failure with preserved ejection fraction. While increased passive stiffness of the myocardium is a suggested mechanism underlying diastolic dysfunction in these hearts, the contribution of active diastolic Ca2+ cycling in cardiomyocytes remains unclear. In this study, we sought to dissect contributions of passive and active mechanisms to diastolic dysfunction in the concentrically hypertrophied heart following pressure-overload. Methods and results Rats were subjected to aortic banding (AB), and experiments were performed 6 weeks after surgery using sham-operated rats as controls. In vivo ejection fraction and fractional shortening were normal, confirming preservation of systolic function. Left ventricular concentric hypertrophy and diastolic dysfunction following AB were indicated by thickening of the ventricular wall, reduced peak early diastolic tissue velocity, and higher E/e' values. Slowed relaxation was also observed in left ventricular muscle strips isolated from AB hearts, during both isometric and isotonic stimulation, and accompanied by increases in passive tension, viscosity, and extracellular collagen. An altered titin phosphorylation profile was observed with hypophosphorylation of the phosphosites S4080 and S3991 sites within the N2Bus, and S12884 within the PEVK region. Increased titin-based stiffness was confirmed by salt-extraction experiments. In contrast, isolated, unloaded cardiomyocytes exhibited accelerated relaxation in AB compared to sham, and less contracture at high pacing frequencies. Parallel enhancement of diastolic Ca2+ handling was observed, with augmented NCX and SERCA2 activity and lowered resting cytosolic [Ca2+]. Conclusion In the hypertrophied heart with preserved systolic function, in vivo diastolic dysfunction develops as cardiac fibrosis and alterations in titin phosphorylation compromise left ventricular compliance, and despite compensatory changes in cardiomyocyte Ca2+ homeostasis.
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MESH Headings
- Adaptation, Physiological
- Animals
- Aorta/physiopathology
- Aorta/surgery
- Arterial Pressure
- Calcium/metabolism
- Calcium Signaling
- Collagen/metabolism
- Compliance
- Connectin/metabolism
- Constriction
- Diastole
- Disease Models, Animal
- Fibrosis
- Hypertrophy, Left Ventricular/metabolism
- Hypertrophy, Left Ventricular/pathology
- Hypertrophy, Left Ventricular/physiopathology
- Isolated Heart Preparation
- Male
- Myocardium/metabolism
- Myocardium/pathology
- Phosphorylation
- Rats, Wistar
- Sarcoplasmic Reticulum Calcium-Transporting ATPases/metabolism
- Sodium-Calcium Exchanger/metabolism
- Systole
- Ventricular Dysfunction, Left/metabolism
- Ventricular Dysfunction, Left/pathology
- Ventricular Dysfunction, Left/physiopathology
- Ventricular Function, Left
- Ventricular Remodeling
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Affiliation(s)
- Åsmund T. Røe
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Ullevål, Kirkeveien 166, NO-0407 Oslo, Norway
- Corresponding author. Tel: +47 23 01 68 00; fax: +47 23 01 67 99, E-mail:
| | - Jan Magnus Aronsen
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Ullevål, Kirkeveien 166, NO-0407 Oslo, Norway
- Bjørknes College, Oslo, Norway
| | - Kristine Skårdal
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Ullevål, Kirkeveien 166, NO-0407 Oslo, Norway
| | - Nazha Hamdani
- Department of Cardiovascular Physiology, Ruhr University Bochum, Bochum, Germany
| | - Wolfgang A. Linke
- Department of Cardiovascular Physiology, Ruhr University Bochum, Bochum, Germany
| | - Håvard E. Danielsen
- Institute for Cancer Genetics and Informatics, Oslo University Hospital, Oslo, Norway
- Centre for Cancer Biomedicine, University of Oslo, Oslo, Norway
- Nuffield Division of Clinical Laboratory Sciences, University of Oxford, Oxford, UK
| | - Ole M. Sejersted
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Ullevål, Kirkeveien 166, NO-0407 Oslo, Norway
| | - Ivar Sjaastad
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Ullevål, Kirkeveien 166, NO-0407 Oslo, Norway
| | - William E. Louch
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Ullevål, Kirkeveien 166, NO-0407 Oslo, Norway
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23
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Abstract
Cardiac contractility is regulated by changes in intracellular Ca concentration ([Ca2+]i). Normal function requires that [Ca2+]i be sufficiently high in systole and low in diastole. Much of the Ca needed for contraction comes from the sarcoplasmic reticulum and is released by the process of calcium-induced calcium release. The factors that regulate and fine-tune the initiation and termination of release are reviewed. The precise control of intracellular Ca cycling depends on the relationships between the various channels and pumps that are involved. We consider 2 aspects: (1) structural coupling: the transporters are organized within the dyad, linking the transverse tubule and sarcoplasmic reticulum and ensuring close proximity of Ca entry to sites of release. (2) Functional coupling: where the fluxes across all membranes must be balanced such that, in the steady state, Ca influx equals Ca efflux on every beat. The remainder of the review considers specific aspects of Ca signaling, including the role of Ca buffers, mitochondria, Ca leak, and regulation of diastolic [Ca2+]i.
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Affiliation(s)
- David A Eisner
- From the Unit of Cardiac Physiology, Division of Cardiovascular Sciences, Manchester Academic Health Sciences Centre, University of Manchester, United Kingdom.
| | - Jessica L Caldwell
- From the Unit of Cardiac Physiology, Division of Cardiovascular Sciences, Manchester Academic Health Sciences Centre, University of Manchester, United Kingdom
| | - Kornél Kistamás
- From the Unit of Cardiac Physiology, Division of Cardiovascular Sciences, Manchester Academic Health Sciences Centre, University of Manchester, United Kingdom
| | - Andrew W Trafford
- From the Unit of Cardiac Physiology, Division of Cardiovascular Sciences, Manchester Academic Health Sciences Centre, University of Manchester, United Kingdom
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24
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Gadeberg HC, Kong CHT, Bryant SM, James AF, Orchard CH. Sarcolemmal distribution of ICa and INCX and Ca 2+ autoregulation in mouse ventricular myocytes. Am J Physiol Heart Circ Physiol 2017; 313:H190-H199. [PMID: 28476922 PMCID: PMC5538864 DOI: 10.1152/ajpheart.00117.2017] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/17/2017] [Revised: 04/14/2017] [Accepted: 05/01/2017] [Indexed: 12/02/2022]
Abstract
This study shows that in contrast to the rat, mouse ventricular Na+/Ca2+ exchange current density is lower in the t-tubules than in the surface sarcolemma and Ca2+ current is predominantly located in the t-tubules. As a consequence, the t-tubules play a role in recovery (autoregulation) from reduced, but not increased, sarcoplasmic reticulum Ca2+ release. The balance of Ca2+ influx and efflux regulates the Ca2+ load of cardiac myocytes, a process known as autoregulation. Previous work has shown that Ca2+ influx, via L-type Ca2+ current (ICa), and efflux, via the Na+/Ca2+ exchanger (NCX), occur predominantly at t-tubules; however, the role of t-tubules in autoregulation is unknown. Therefore, we investigated the sarcolemmal distribution of ICa and NCX current (INCX), and autoregulation, in mouse ventricular myocytes using whole cell voltage-clamp and simultaneous Ca2+ measurements in intact and detubulated (DT) cells. In contrast to the rat, INCX was located predominantly at the surface membrane, and the hysteresis between INCX and Ca2+ observed in intact myocytes was preserved after detubulation. Immunostaining showed both NCX and ryanodine receptors (RyRs) at the t-tubules and surface membrane, consistent with colocalization of NCX and RyRs at both sites. Unlike INCX, ICa was found predominantly in the t-tubules. Recovery of the Ca2+ transient amplitude to steady state (autoregulation) after application of 200 µM or 10 mM caffeine was slower in DT cells than in intact cells. However, during application of 200 µM caffeine to increase sarcoplasmic reticulum (SR) Ca2+ release, DT and intact cells recovered at the same rate. It appears likely that this asymmetric response to changes in SR Ca2+ release is a consequence of the distribution of ICa, which is reduced in DT cells and is required to refill the SR after depletion, and NCX, which is little affected by detubulation, remaining available to remove Ca2+ when SR Ca2+ release is increased. NEW & NOTEWORTHY This study shows that in contrast to the rat, mouse ventricular Na+/Ca2+ exchange current density is lower in the t-tubules than in the surface sarcolemma and Ca2+ current is predominantly located in the t-tubules. As a consequence, the t-tubules play a role in recovery (autoregulation) from reduced, but not increased, sarcoplasmic reticulum Ca2+ release.
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Affiliation(s)
- Hanne C Gadeberg
- School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, United Kingdom
| | - Cherrie H T Kong
- School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, United Kingdom
| | - Simon M Bryant
- School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, United Kingdom
| | - Andrew F James
- School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, United Kingdom
| | - Clive H Orchard
- School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, United Kingdom
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25
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Different Densities of Na-Ca Exchange Current in T-Tubular and Surface Membranes and Their Impact on Cellular Activity in a Model of Rat Ventricular Cardiomyocyte. BIOMED RESEARCH INTERNATIONAL 2017; 2017:6343821. [PMID: 28321411 PMCID: PMC5340987 DOI: 10.1155/2017/6343821] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/01/2016] [Revised: 12/18/2016] [Accepted: 01/04/2017] [Indexed: 01/13/2023]
Abstract
The ratio of densities of Na-Ca exchanger current (INaCa) in the t-tubular and surface membranes (INaCa-ratio) computed from the values of INaCa and membrane capacitances (Cm) measured in adult rat ventricular cardiomyocytes before and after detubulation ranges between 1.7 and 25 (potentially even 40). Variations of action potential waveform and of calcium turnover within this span of the INaCa-ratio were simulated employing previously developed model of rat ventricular cell incorporating separate description of ion transport systems in the t-tubular and surface membranes. The increase of INaCa-ratio from 1.7 to 25 caused a prolongation of APD (duration of action potential at 90% repolarisation) by 12, 9, and 6% and an increase of peak intracellular Ca2+ transient by 45, 19, and 6% at 0.1, 1, and 5 Hz, respectively. The prolonged APD resulted from the increase of INaCa due to the exposure of a larger fraction of Na-Ca exchangers to higher Ca2+ transients under the t-tubular membrane. The accompanying rise of Ca2+ transient was a consequence of a higher Ca2+ load in sarcoplasmic reticulum induced by the increased Ca2+ cycling between the surface and t-tubular membranes. However, the reason for large differences in the INaCa-ratio assessed from measurements in adult rat cardiomyocytes remains to be explained.
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26
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Chu L, Greenstein JL, Winslow RL. Modeling Na +-Ca 2+ exchange in the heart: Allosteric activation, spatial localization, sparks and excitation-contraction coupling. J Mol Cell Cardiol 2016; 99:174-187. [PMID: 27377851 DOI: 10.1016/j.yjmcc.2016.06.068] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/18/2016] [Revised: 06/14/2016] [Accepted: 06/30/2016] [Indexed: 01/19/2023]
Abstract
The cardiac sodium (Na+)/calcium (Ca2+) exchanger (NCX1) is an electrogenic membrane transporter that regulates Ca2+ homeostasis in cardiomyocytes, serving mainly to extrude Ca2+ during diastole. The direction of Ca2+ transport reverses at membrane potentials near that of the action potential plateau, generating an influx of Ca2+ into the cell. Therefore, there has been great interest in the possible roles of NCX1 in cardiac Ca2+-induced Ca2+ release (CICR). Interest has been reinvigorated by a recent super-resolution optical imaging study suggesting that ~18% of NCX1 co-localize with ryanodine receptor (RyR2) clusters, and ~30% of additional NCX1 are localized to within ~120nm of the nearest RyR2. NCX1 may therefore occupy a privileged position in which to modulate CICR. To examine this question, we have developed a mechanistic biophysically-detailed model of NCX1 that describes both NCX1 transport kinetics and Ca2+-dependent allosteric regulation. This NCX1 model was incorporated into a previously developed super-resolution model of the Ca2+ spark as well as a computational model of the cardiac ventricular myocyte that includes a detailed description of CICR with stochastic gating of L-type Ca2+ channels and RyR2s, and that accounts for local Ca2+ gradients near the dyad via inclusion of a peri-dyadic (PD) compartment. Both models predict that increasing the fraction of NCX1 in the dyad and PD decreases spark frequency, fidelity, and diastolic Ca2+ levels. Spark amplitude and duration are less sensitive to NCX1 spatial redistribution. On the other hand, NCX1 plays an important role in promoting Ca2+ entry into the dyad, and hence contributing to the trigger for RyR2 release at depolarized membrane potentials and in the presence of elevated local Na+ concentration. Whole-cell simulation of NCX1 tail currents are consistent with the finding that a relatively high fraction of NCX1 (~45%) resides in the dyadic and PD spaces, with a dyad-to-PD ratio of roughly 1:2. Allosteric Ca2+ activation of NCX1 helps to "functionally localize" exchanger activity to the dyad and PD by reducing exchanger activity in the cytosol thereby protecting the cell from excessive loss of Ca2+ during diastole.
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Affiliation(s)
- Lulu Chu
- Department of Biomedical Engineering and the Institute for Computational Medicine, The Johns Hopkins University School of Medicine and Whiting School of Engineering, 3400 N Charles Street, Baltimore, MD, 21218, USA.
| | - Joseph L Greenstein
- Department of Biomedical Engineering and the Institute for Computational Medicine, The Johns Hopkins University School of Medicine and Whiting School of Engineering, 3400 N Charles Street, Baltimore, MD, 21218, USA.
| | - Raimond L Winslow
- Department of Biomedical Engineering and the Institute for Computational Medicine, The Johns Hopkins University School of Medicine and Whiting School of Engineering, 3400 N Charles Street, Baltimore, MD, 21218, USA.
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27
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Abstract
Na(+)/Ca(2+) exchangers (NCXs) have traditionally been viewed principally as a means of Ca(2+) removal from non-excitable cells. However there has recently been increasing interest in the operation of NCXs in reverse mode acting as a means of eliciting Ca(2+) entry into these cells. Reverse mode exchange requires a significant change in the normal resting transmembrane ion gradients and membrane potential, which has been suggested to occur principally via the coupling of NCXs to localised Na(+) entry through non-selective cation channels such as canonical transient receptor potential (TRPC) channels. Here we review evidence for functional or physical coupling of NCXs to non-selective cation channels, and how this affects NCX activity in non-excitable cells. In particular we focus on the potential role of nanojunctions, where the close apposition of plasma and intracellular membranes may help create the conditions needed for the generation of localised rises in Na(+) concentration that would be required to trigger reverse mode exchange.
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28
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Balycheva M, Faggian G, Glukhov AV, Gorelik J. Microdomain-specific localization of functional ion channels in cardiomyocytes: an emerging concept of local regulation and remodelling. Biophys Rev 2015; 7:43-62. [PMID: 28509981 PMCID: PMC5425752 DOI: 10.1007/s12551-014-0159-x] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2014] [Accepted: 12/18/2014] [Indexed: 12/26/2022] Open
Abstract
Cardiac excitation involves the generation of action potential by individual cells and the subsequent conduction of the action potential from cell to cell through intercellular gap junctions. Excitation of the cellular membrane results in opening of the voltage-gated L-type calcium ion (Ca2+) channels, thereby allowing a small amount of Ca2+ to enter the cell, which in turn triggers the release of a much greater amount of Ca2+ from the sarcoplasmic reticulum, the intracellular Ca2+ store, and gives rise to the systolic Ca2+ transient and contraction. These processes are highly regulated by the autonomic nervous system, which ensures the acute and reliable contractile function of the heart and the short-term modulation of this function upon changes in heart rate or workload. It has recently become evident that discrete clusters of different ion channels and regulatory receptors are present in the sarcolemma, where they form an interacting network and work together as a part of a macro-molecular signalling complex which in turn allows the specificity, reliability and accuracy of the autonomic modulation of the excitation-contraction processes by a variety of neurohormonal pathways. Disruption in subcellular targeting of ion channels and associated signalling proteins may contribute to the pathophysiology of a variety of cardiac diseases, including heart failure and certain arrhythmias. Recent methodological advances have made it possible to routinely image the topography of live cardiomyocytes, allowing the study of clustering functional ion channels and receptors as well as their coupling within a specific microdomain. In this review we highlight the emerging understanding of the functionality of distinct subcellular microdomains in cardiac myocytes (e.g. T-tubules, lipid rafts/caveolae, costameres and intercalated discs) and their functional role in the accumulation and regulation of different subcellular populations of sodium, Ca2+ and potassium ion channels and their contributions to cellular signalling and cardiac pathology.
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Affiliation(s)
- Marina Balycheva
- Department of Cardiovascular Sciences, National Heart and Lung Institute, Imperial Centre for Translational and Experimental Medicine, Imperial College London, 4th Floor National Heart and Lung Institute, Hammersmith Campus, Du Cane Road, London, W12 0NN, UK
- Cardiosurgery Department, University of Verona School of Medicine, Verona, Italy
| | - Giuseppe Faggian
- Cardiosurgery Department, University of Verona School of Medicine, Verona, Italy
| | - Alexey V Glukhov
- Department of Cardiovascular Sciences, National Heart and Lung Institute, Imperial Centre for Translational and Experimental Medicine, Imperial College London, 4th Floor National Heart and Lung Institute, Hammersmith Campus, Du Cane Road, London, W12 0NN, UK.
| | - Julia Gorelik
- Department of Cardiovascular Sciences, National Heart and Lung Institute, Imperial Centre for Translational and Experimental Medicine, Imperial College London, 4th Floor National Heart and Lung Institute, Hammersmith Campus, Du Cane Road, London, W12 0NN, UK.
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29
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Hillestad V, Espe EKS, Cero F, Larsen KO, Sjaastad I, Nygård S, Skjønsberg OH, Christensen G. IL-18 neutralization during alveolar hypoxia improves left ventricular diastolic function in mice. Acta Physiol (Oxf) 2015; 213:492-504. [PMID: 25182570 DOI: 10.1111/apha.12376] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2014] [Revised: 06/30/2014] [Accepted: 08/27/2014] [Indexed: 12/18/2022]
Abstract
AIM In patients, an association exists between pulmonary diseases and diastolic dysfunction of the left ventricle (LV). We have previously shown that alveolar hypoxia in mice induces LV diastolic dysfunction and that mice exposed to hypoxia have increased levels of circulating interleukin-18 (IL-18), suggesting involvement of IL-18 in development of diastolic dysfunction. IL-18 binding protein (IL-18BP) is a natural inhibitor of IL-18. In this study, we hypothesized that neutralization of IL-18 during alveolar hypoxia would improve LV diastolic function. METHODS Mice were exposed to 10% oxygen for 2 weeks while treated with IL-18BP or vehicle. Cardiac function and morphology were measured using echocardiography, intraventricular pressure measurements and magnetic resonance imaging (MRI). For characterization of molecular changes in the heart, both real-time PCR and Western blotting were performed. ELISA technique was used to measure levels of circulating cytokines. RESULTS As expected, exposure to hypoxia-induced LV diastolic dysfunction, as shown by prolonged time constant of isovolumic relaxation (τ). Improved relaxation with IL-18BP treatment was demonstrated by a significant reduction towards control τ values. Decreased levels of phosphorylated phospholamban (P-PLB) in hypoxia, but normalization by IL-18BP treatment suggest a role for IL-18 in regulation of calcium-handling proteins in hypoxia-induced diastolic dysfunction. In addition, MRI showed less increase in right ventricular (RV) wall thickness in IL-18BP-treated animals exposed to hypoxia, indicating an effect on RV hypertrophy. CONCLUSION Neutralization of IL-18 during alveolar hypoxia improves LV diastolic function and partly prevents RV hypertrophy.
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Affiliation(s)
- V. Hillestad
- Institute for Experimental Medical Research; Oslo University Hospital Ullevål and University of Oslo; Oslo Norway
- KG Jebsen Cardiac Research Center; University of Oslo; Oslo Norway
- Center for Heart Failure Research; University of Oslo; Oslo Norway
| | - E. K. S. Espe
- Institute for Experimental Medical Research; Oslo University Hospital Ullevål and University of Oslo; Oslo Norway
- KG Jebsen Cardiac Research Center; University of Oslo; Oslo Norway
- Center for Heart Failure Research; University of Oslo; Oslo Norway
| | - F. Cero
- Institute for Experimental Medical Research; Oslo University Hospital Ullevål and University of Oslo; Oslo Norway
- KG Jebsen Cardiac Research Center; University of Oslo; Oslo Norway
- Center for Heart Failure Research; University of Oslo; Oslo Norway
- Departement of Pulmonary Medicine; Oslo University Hospital Ullevål and University of Oslo; Oslo Norway
| | - K. O. Larsen
- Institute for Experimental Medical Research; Oslo University Hospital Ullevål and University of Oslo; Oslo Norway
- KG Jebsen Cardiac Research Center; University of Oslo; Oslo Norway
- Center for Heart Failure Research; University of Oslo; Oslo Norway
- Departement of Pulmonary Medicine; Oslo University Hospital Ullevål and University of Oslo; Oslo Norway
| | - I. Sjaastad
- Institute for Experimental Medical Research; Oslo University Hospital Ullevål and University of Oslo; Oslo Norway
- KG Jebsen Cardiac Research Center; University of Oslo; Oslo Norway
- Center for Heart Failure Research; University of Oslo; Oslo Norway
| | - S. Nygård
- Institute for Experimental Medical Research; Oslo University Hospital Ullevål and University of Oslo; Oslo Norway
- KG Jebsen Cardiac Research Center; University of Oslo; Oslo Norway
- Center for Heart Failure Research; University of Oslo; Oslo Norway
- Bioinformatics Core Facility; Institute for Medical Informatics; Oslo University Hospital and University of Oslo; Oslo Norway
| | - O. H. Skjønsberg
- Departement of Pulmonary Medicine; Oslo University Hospital Ullevål and University of Oslo; Oslo Norway
| | - G. Christensen
- Institute for Experimental Medical Research; Oslo University Hospital Ullevål and University of Oslo; Oslo Norway
- KG Jebsen Cardiac Research Center; University of Oslo; Oslo Norway
- Center for Heart Failure Research; University of Oslo; Oslo Norway
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30
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Lin X, O'Malley H, Chen C, Auerbach D, Foster M, Shekhar A, Zhang M, Coetzee W, Jalife J, Fishman GI, Isom L, Delmar M. Scn1b deletion leads to increased tetrodotoxin-sensitive sodium current, altered intracellular calcium homeostasis and arrhythmias in murine hearts. J Physiol 2014; 593:1389-407. [PMID: 25772295 DOI: 10.1113/jphysiol.2014.277699] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2014] [Accepted: 08/07/2014] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS Na(+) current (INa) results from the integrated function of a molecular aggregate (the voltage-gated Na(+) channel complex) that includes the β subunit family. Mutations or rare variants in Scn1b (encoding the β1 and β1B subunits) have been associated with various inherited arrhythmogenic syndromes, including Brugada syndrome and sudden unexpected death in patients with epilepsy. We used Scn1b null mice to understand better the relation between Scn1b expression, and cardiac electrical function. Loss of Scn1b caused, among other effects, increased amplitude of tetrodotoxin-sensitive INa, delayed after-depolarizations, triggered beats, delayed Ca(2+) transients, frequent spontaneous calcium release events and increased susceptibility to polymorphic ventricular arrhythmias. Most alterations in Ca(2+) homeostasis were prevented by 100 nM tetrodotoxin. We propose that life-threatening arrhythmias in patients with mutations in Scn1b, a gene classically defined as ancillary to the Na(+) channel α subunit, can be partly consequent to disrupted intracellular Ca(2+) homeostasis. ABSTRACT Na(+) current (INa) is determined not only by the properties of the pore-forming voltage-gated Na(+) channel (VGSC) α subunit, but also by the integrated function of a molecular aggregate (the VGSC complex) that includes the VGSC β subunit family. Mutations or rare variants in Scn1b (encoding the β1 and β1B subunits) have been associated with various inherited arrhythmogenic syndromes, including cases of Brugada syndrome and sudden unexpected death in patients with epilepsy. Here, we have used Scn1b null mouse models to understand better the relation between Scn1b expression, and cardiac electrical function. Using a combination of macropatch and scanning ion conductance microscopy we show that loss of Scn1b in juvenile null animals resulted in increased tetrodotoxin-sensitive INa but only in the cell midsection, even before full T-tubule formation; the latter occurred concurrent with increased message abundance for the neuronal Scn3a mRNA, suggesting increased abundance of tetrodotoxin-sensitive NaV 1.3 protein and yet its exclusion from the region of the intercalated disc. Ventricular myocytes from cardiac-specific adult Scn1b null animals showed increased Scn3a message, prolonged action potential repolarization, presence of delayed after-depolarizations and triggered beats, delayed Ca(2+) transients and frequent spontaneous Ca(2+) release events and at the whole heart level, increased susceptibility to polymorphic ventricular arrhythmias. Most alterations in Ca(2+) homeostasis were prevented by 100 nM tetrodotoxin. Our results suggest that life-threatening arrhythmias in patients with mutations in Scn1b, a gene classically defined as ancillary to the Na(+) channel α subunit, can be partly consequent to disrupted intracellular Ca(2+) homeostasis in ventricular myocytes.
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Affiliation(s)
- Xianming Lin
- Leon H. Charney Division of Cardiology, New York University School of Medicine, New York, NY, USA
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Wang HS, Chen Y, Vairamani K, Shull GE. Critical role of bicarbonate and bicarbonate transporters in cardiac function. World J Biol Chem 2014; 5:334-345. [PMID: 25225601 PMCID: PMC4160527 DOI: 10.4331/wjbc.v5.i3.334] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/01/2014] [Revised: 03/06/2014] [Accepted: 05/19/2014] [Indexed: 02/05/2023] Open
Abstract
Bicarbonate is one of the major anions in mammalian tissues and extracellular fluids. Along with accompanying H+, HCO3- is generated from CO2 and H2O, either spontaneously or via the catalytic activity of carbonic anhydrase. It serves as a component of the major buffer system, thereby playing a critical role in pH homeostasis. Bicarbonate can also be utilized by a variety of ion transporters, often working in coupled systems, to transport other ions and organic substrates across cell membranes. The functions of HCO3- and HCO3--transporters in epithelial tissues have been studied extensively, but their functions in heart are less well understood. Here we review studies of the identities and physiological functions of Cl-/HCO3- exchangers and Na+/HCO3- cotransporters of the SLC4A and SLC26A families in heart. We also present RNA Seq analysis of their cardiac mRNA expression levels. These studies indicate that slc4a3 (AE3) is the major Cl-/HCO3- exchanger and plays a protective role in heart failure, and that Slc4a4 (NBCe1) is the major Na+/HCO3- cotransporter and affects action potential duration. In addition, previous studies show that HCO3- has a positive inotropic effect in the perfused heart that is largely independent of effects on intracellular Ca2+. The importance of HCO3- in the regulation of contractility is supported by experiments showing that isolated cardiomyocytes exhibit sharply enhanced contractility, with no change in Ca2+ transients, when switched from Hepes-buffered to HCO3-- buffered solutions. These studies demonstrate that HCO3- and HCO3--handling proteins play important roles in the regulation of cardiac function.
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Ferrantini C, Crocini C, Coppini R, Vanzi F, Tesi C, Cerbai E, Poggesi C, Pavone FS, Sacconi L. The transverse-axial tubular system of cardiomyocytes. Cell Mol Life Sci 2013; 70:4695-710. [PMID: 23846763 PMCID: PMC11113601 DOI: 10.1007/s00018-013-1410-5] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2013] [Revised: 06/03/2013] [Accepted: 06/13/2013] [Indexed: 10/26/2022]
Abstract
A characteristic histological feature of striated muscle cells is the presence of deep invaginations of the plasma membrane (sarcolemma), most commonly referred to as T-tubules or the transverse-axial tubular system (TATS). TATS mediates the rapid spread of the electrical signal (action potential) to the cell core triggering Ca(2+) release from the sarcoplasmic reticulum, ultimately inducing myofilament contraction (excitation-contraction coupling). T-tubules, first described in vertebrate skeletal muscle cells, have also been recognized for a long time in mammalian cardiac ventricular myocytes, with a structure and a function that in recent years have been shown to be far more complex and pivotal for cardiac function than initially thought. Renewed interest in T-tubule function stems from the loss and disorganization of T-tubules found in a number of pathological conditions including human heart failure (HF) and dilated and hypertrophic cardiomyopathies, as well as in animal models of HF, chronic ischemia and atrial fibrillation. Disease-related remodeling of the TATS leads to asynchronous and inhomogeneous Ca(2+)-release, due to the presence of orphan ryanodine receptors that have lost their coupling with the dihydropyridine receptors and are either not activated or activated with a delay. Here, we review the physiology of the TATS, focusing first on the relationship between function and structure, and then describing T-tubular remodeling and its reversal in disease settings and following effective therapeutic approaches.
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Affiliation(s)
- C. Ferrantini
- Division of Physiology, Department of Clinical and Experimental Medicine, University of Florence, Florence, Italy
- Centre of Molecular Medicine (C.I.M.M.B.A.), University of Florence, Florence, Italy
| | - C. Crocini
- European Laboratory for Non-Linear Spectroscopy (LENS), University of Florence, Sesto Fiorentino, Italy
| | - R. Coppini
- Centre of Molecular Medicine (C.I.M.M.B.A.), University of Florence, Florence, Italy
- Division of Pharmacology, Department “NeuroFarBa”, University of Florence, Florence, Italy
| | - F. Vanzi
- European Laboratory for Non-Linear Spectroscopy (LENS), University of Florence, Sesto Fiorentino, Italy
- Department of Biology, University of Florence, Florence, Italy
| | - C. Tesi
- Division of Physiology, Department of Clinical and Experimental Medicine, University of Florence, Florence, Italy
- Centre of Molecular Medicine (C.I.M.M.B.A.), University of Florence, Florence, Italy
| | - E. Cerbai
- Centre of Molecular Medicine (C.I.M.M.B.A.), University of Florence, Florence, Italy
- Division of Pharmacology, Department “NeuroFarBa”, University of Florence, Florence, Italy
| | - C. Poggesi
- Division of Physiology, Department of Clinical and Experimental Medicine, University of Florence, Florence, Italy
- Centre of Molecular Medicine (C.I.M.M.B.A.), University of Florence, Florence, Italy
| | - F. S. Pavone
- European Laboratory for Non-Linear Spectroscopy (LENS), University of Florence, Sesto Fiorentino, Italy
- Department of Physics and Astronomy, University of Florence, Sesto Fiorentino, Italy
- National Institute of Optics (INO), National Research Council (CNR), Florence, Italy
| | - L. Sacconi
- European Laboratory for Non-Linear Spectroscopy (LENS), University of Florence, Sesto Fiorentino, Italy
- National Institute of Optics (INO), National Research Council (CNR), Florence, Italy
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Expression and localization of TRPC proteins in rat ventricular myocytes at various developmental stages. Cell Tissue Res 2013; 355:201-12. [PMID: 24146259 DOI: 10.1007/s00441-013-1733-4] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2013] [Accepted: 09/02/2013] [Indexed: 12/22/2022]
Abstract
Growing evidence indicates that transient receptor potential canonical (TRPC) channels play important roles in various Ca(2+)-mediated physiological and pathophysiological processes, including development. Many types of TRPC proteins are expressed in the heart. However, limited data are available comparing the expression and localization among TRPC proteins in the ventricular myocyte at various developmental stages. Our purpose is to investigate the expression and localization profile of TRPC proteins in ventricular myocytes of fetal (18.5 days), neonatal (< 24 h after birth) and adult (8 week old) rats. Western blotting, immunofluorescence and confocal laser scanning microscopy were employed. TRPC1/3-6 proteins were expressed in the rat ventricle throughout the three developmental stages. The expression profile of TRPC1/3/4 in the ventricle followed an upward trend from the fetus to the adult. By contrast, TRPC6 in the ventricle was expressed at the highest level in the fetal group and was sharply down-regulated immediately after birth. TRPC5 expression in the ventricle did not change significantly during the three stages. TRPC1/3/5/6 proteins were localized to the T-tubule and TRPC1/3/4/6 to intercalated disks in adult myocytes. The wide spatiotemporal overlap and dynamic regulation of TRPC expression in ventricular myocytes indicates potential complex combinations and redundancy of native TRPC proteins in the heart and gives important clues for further investigations into the exact subunit compositions and functional properties of native TRPC channels in the heart.
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Agonist activated PKCβII translocation and modulation of cardiac myocyte contractile function. Sci Rep 2013; 3:1971. [PMID: 23756828 PMCID: PMC3679501 DOI: 10.1038/srep01971] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2013] [Accepted: 05/22/2013] [Indexed: 11/26/2022] Open
Abstract
Elevated protein kinase C βII (PKCβII) expression develops during heart failure and yet the role of this isoform in modulating contractile function remains controversial. The present study examines the impact of agonist-induced PKCβII activation on contractile function in adult cardiac myocytes. Diminished contractile function develops in response to low dose phenylephrine (PHE, 100 nM) in controls, while function is preserved in response to PHE in PKCβII-expressing myocytes. PHE also caused PKCβII translocation and a punctate distribution pattern in myocytes expressing this isoform. The preserved contractile function and translocation responses to PHE are blocked by the inhibitor, LY379196 (30 nM) in PKCβII-expressing myocytes. Further analysis showed downstream protein kinase D (PKD) phosphorylation and phosphatase activation are associated with the LY379196-sensitive contractile response. PHE also triggered a complex pattern of end-target phosphorylation in PKCβII-expressing myocytes. These patterns are consistent with bifurcated activation of downstream signaling activity by PKCβII.
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Aronsen JM, Swift F, Sejersted OM. Cardiac sodium transport and excitation-contraction coupling. J Mol Cell Cardiol 2013; 61:11-9. [PMID: 23774049 DOI: 10.1016/j.yjmcc.2013.06.003] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/17/2013] [Revised: 05/17/2013] [Accepted: 06/05/2013] [Indexed: 01/12/2023]
Abstract
The excitation-contraction coupling (EC-coupling) links membrane depolarization with contraction in cardiomyocytes. Ca(2+) induced opening of ryanodine receptors (RyRs) leads to Ca(2+) induced Ca(2+) release (CICR) from the sarcoplasmic reticulum (SR) into the dyadic cleft between the t-tubules and SR. Ca(2+) is removed from the cytosol by the SR Ca(2+) ATPase (SERCA2) and the Na,Ca-exchanger (NCX). The NCX connects cardiac Ca(2+) and Na(+)-transport, leading to Na(+)-dependent regulation of EC-coupling by several mechanisms of which some still lack firm experimental evidence. Firstly, NCX might contribute to CICR during an action potential (AP) as Na(+)-accumulation at the intracellular site together with depolarization will trigger reverse mode exchange bringing Ca(2+) into the dyadic cleft. The controversial issue is the nature of the compartment in which Na(+) accumulates. It seems not to be the bulk cytosol, but is it part of a widespread subsarcolemmal space, a localized microdomain ("fuzzy space"), or as we propose, a more localized "spot" to which only a few membrane proteins have shared access (nanodomains)? Also, there seems to be spots where the Na,K-pump (NKA) will cause local Na(+) depletion. Secondly, Na(+) determines the rate of cytosolic Ca(2+) removal and SR Ca(2+) load by regulating the SERCA2/NCX-balance during the decay of the Ca(2+) transient. The aim of this review is to describe available data and current concepts of Na(+)-mediated regulation of cardiac EC-coupling, with special focus on subcellular microdomains and the potential roles of Na(+) transport proteins in regulating CICR and Ca(2+) extrusion in cardiomyocytes. We propose that voltage gated Na(+) channels, NCX and the NKA α2-isoform all regulate cardiac EC-coupling through control of the "Na(+) concentration in specific subcellular nanodomains in cardiomyocytes. This article is part of a Special Issue entitled "Na(+) Regulation in Cardiac Myocytes."
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Affiliation(s)
- J M Aronsen
- Institute for Experimental Medical Research, Oslo University Hospital Ullevål and University of Oslo, Oslo, Norway
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Trafford AW, Clarke JD, Richards MA, Eisner DA, Dibb KM. Calcium signalling microdomains and the t-tubular system in atrial mycoytes: potential roles in cardiac disease and arrhythmias. Cardiovasc Res 2013; 98:192-203. [PMID: 23386275 DOI: 10.1093/cvr/cvt018] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
The atria contribute 25% to ventricular stroke volume and are the site of the commonest cardiac arrhythmia, atrial fibrillation (AF). The initiation of contraction in the atria is similar to that in the ventricle involving a systolic rise of intracellular Ca(2+) concentration ([Ca(2+)](i)). There are, however, substantial inter-species differences in the way systolic Ca(2+) is regulated in atrial cells. These differences are a consequence of a well-developed and functionally relevant transverse (t)-tubule network in the atria of large mammals, including humans, and its virtual absence in smaller laboratory species such as the rat. Where T-tubules are absent, the systolic Ca(2+) transient results from a 'fire-diffuse-fire' sequential recruitment of Ca(2+) release sites from the cell edge to the centre and hence marked spatiotemporal heterogeneity of systolic Ca(2+). Conversely, the well-developed T-tubule network in large mammals ensures a near synchronous rise of [Ca(2+)](i). In addition to synchronizing the systolic rise of [Ca(2+)](i), the presence of T-tubules in the atria of large mammals, by virtue of localization of the L-type Ca(2+) channels and Na(+)-Ca(2+) exchanger antiporters on the T-tubules, may serve to, respectively, accelerate changes in the amplitude of the systolic Ca(2+) transient during inotropic manoeuvres and lower diastolic [Ca(2+)](i). On the other hand, the presence of T-tubules and hence wider cellular distribution of the Na(+)-Ca(2+) exchanger may predispose the atria of large mammals to Ca(2+)-dependent delayed afterdepolarizations (DADs); this may be a determining factor in why the atria of large mammals spontaneously develop and maintain AF.
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Affiliation(s)
- Andrew W Trafford
- Unit of Cardiac Physiology, Manchester Academic Health Science Centre, Institute of Cardiovascular Science, University of Manchester, 3.23 Core Technology Facility, 46 Grafton Street, Manchester M13 9PT, UK
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37
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Ca2+ channel and Na+/Ca2+ exchange localization in cardiac myocytes. J Mol Cell Cardiol 2013; 58:22-31. [DOI: 10.1016/j.yjmcc.2012.11.022] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/21/2012] [Revised: 11/20/2012] [Accepted: 11/28/2012] [Indexed: 01/01/2023]
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38
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Ginsburg KS, Weber CR, Bers DM. Cardiac Na+-Ca2+ exchanger: dynamics of Ca2+-dependent activation and deactivation in intact myocytes. J Physiol 2013; 591:2067-86. [PMID: 23401616 PMCID: PMC3634520 DOI: 10.1113/jphysiol.2013.252080] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2013] [Accepted: 02/10/2013] [Indexed: 01/05/2023] Open
Abstract
Cardiac Na(+)-Ca(2+) exchange (NCX) activity is regulated by [Ca(2+)]i. The physiological role and dynamics of this process in intact cardiomyocytes are largely unknown. We examined NCX Ca(2+) activation in intact rabbit and mouse cardiomyocytes at 37°C. Sarcoplasmic reticulum (SR) function was blocked, and cells were bathed in 2 mm Ca(2+). We probed Ca(2+) activation without voltage clamp by applying Na(+)-free (0 Na(+)) solution for 5 s bouts, repeated each 10 s, which should evoke [Ca(2+)]i transients due to Ca(2+) influx via NCX. In rested rabbit myocytes, Ca(2+) influx was undetectable even after 0 Na(+) applications were repeated for 2-5 min or more, suggesting that NCX was inactive. After external electric field stimulation pulses were applied, to admit Ca(2+) via L-type Ca(2+) channels, 0 Na(+) bouts activated Ca(2+) influx efficaciously, indicating that NCX had become active. Calcium activation increased with more field pulses, reaching a maximum typically after 15-20 pulses (1 Hz). At rest, NCX deactivated with a time constant typically of 20-40 s. An increase in [Na(+)]i, either in rabbit cardiomyocytes as a result of inhibition of Na(+)-K(+) pumping, or in mouse cardiomyocytes where normal [Na(+)]i is higher vs. rabbit, sensitized NCX to self-activation by 0 Na(+) bouts. In experiments with the SR functional but initially empty, the activation time course was slowed. It is possible that the SR initially accumulated Ca(2+) that would otherwise cause activation. We modelled Ca(2+) activation as a fourth-order highly co-operative process ([Ca]i required for half-activation K0.5act = 375 nm), with dynamics severalfold slower than the cardiac cycle. We incorporated this NCX model into an established ventricular myocyte model, which allowed us to predict responses to twitch stimulation in physiological conditions with the SR intact. Model NCX fractional activation increased from 0.1 to 1.0 as the frequency was increased from 0.2 to 2 Hz. By adjusting Ca(2+) activation on a multibeat time scale, NCX might better maintain a stable long-term Ca(2+) balance while contributing to the ability of myocytes to produce Ca(2+) transients over a wide range of intensity.
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Affiliation(s)
- Kenneth S Ginsburg
- Department of Pharmacology, University of California Davis, Davis, CA 95616, USA
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39
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Louch WE, Stokke MK, Sjaastad I, Christensen G, Sejersted OM. No rest for the weary: diastolic calcium homeostasis in the normal and failing myocardium. Physiology (Bethesda) 2013; 27:308-23. [PMID: 23026754 DOI: 10.1152/physiol.00021.2012] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Following contraction of the heart, efficient relaxation (diastole) is essential for refilling the ventricles with blood. This review describes how ventricular relaxation is controlled by Ca(2+) homeostasis in cardiac muscle cells and how alterations in Ca(2+) cycling affect diastolic function in the normal and failing heart. These discussions illustrate that the diastolic phase is not simply a period of rest but rather involves highly regulated and dynamic Ca(2+) fluxes.
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Affiliation(s)
- William E Louch
- Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, Oslo, Norway.
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40
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Kortenoeven MLA, Pedersen NB, Miller RL, Rojek A, Fenton RA. Genetic ablation of aquaporin-2 in the mouse connecting tubules results in defective renal water handling. J Physiol 2013; 591:2205-19. [PMID: 23359673 DOI: 10.1113/jphysiol.2012.250852] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Body water balance is regulated via the water channel aquaporin-2 (AQP2), which is expressed in the renal connecting tubule (CNT) and collecting duct (CD). The relative roles of AQP2 in the CNT and CD are not fully understood. To study the role of AQP2 in the CNT we generated a mouse model with CNT-specific AQP2 deletion (AQP2-CNT-knockout (KO)). Confocal laser scanning microscopy and immunogold electron microscopy demonstrated an absence of AQP2 in the CNT of AQP2-CNT-KO mice. Twenty-four hour urine output was significantly increased (KO: 3.0 ± 0.3 ml (20 g body weight (BW))(-1); wild-type (WT): 1.9 ± 0.3 ml (20 g BW)(-1)) and urine osmolality decreased (KO: 1179 ± 107 mosmol kg(-1); WT: 1790 ± 146 mosmol kg(-1)) in AQP2-CNT-KO mice compared with controls. After 24 h water restriction, urine osmolality was still significantly lower in AQP2-CNT-KO mice (KO: 2087 ± 169 mosmol kg(-1); WT: 2678 ± 144 mosmol kg(-1)). A significant difference in urine osmolality between groups before desmopressin (dDAVP) (KO: 873 ± 129 mosmol kg(-1); WT: 1387 ± 163 mosmol kg(-1)) was not apparent 2 h after injection, with urine osmolality increased significantly in both groups (KO: 2944 ± 41 mosmol kg(-1); WT: 3133 ± 66 mosmol kg(-1)). Cortical kidney fractions from AQP2-CNT-KO mice had significantly reduced AQP2, with no compensatory changes in sodium potassium chloride cotransporter (NKCC2), AQP3 or AQP4. Lithium chloride treatment increased urine volume and decreased osmolality in both WT and AQP2-CNT-KO mice. After 8 days of treatment, the AQP2-CNT-KO mice still had a significantly higher urine volume and lower urine osmolality, suggesting that the CNT does not play a significant role in the pathology of lithium-induced nephrogenic diabetes insipidus. Our studies indicate that the CNT plays a role in regulating body water balance under basal conditions, but not for maximal concentration of the urine during antidiuresis.
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Cheng Y, Kekenes-Huskey P, Hake J, Holst M, McCammon J, Michailova A. Multi-Scale Continuum Modeling of Biological Processes: From Molecular Electro-Diffusion to Sub-Cellular Signaling Transduction. ACTA ACUST UNITED AC 2012; 5. [PMID: 23505398 DOI: 10.1088/1749-4699/5/1/015002] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
This article provides a brief review of multi-scale modeling at the molecular to cellular scale, with new results for heart muscle cells. A finite element-based simulation package (SMOL) was used to investigate the signaling transduction at molecular and sub-cellular scales (http://mccammon.ucsd.edu/smol/, http://FETK.org) by numerical solution of time-dependent Smoluchowski equations and a reaction-diffusion system. At the molecular scale, SMOL has yielded experimentally-validated estimates of the diffusion-limited association rates for the binding of acetylcholine to mouse acetylcholinesterase using crystallographic structural data. The predicted rate constants exhibit increasingly delayed steady-state times with increasing ionic strength and demonstrate the role of an enzyme's electrostatic potential in influencing ligand binding. At the sub-cellular scale, an extension of SMOL solves a non-linear, reaction-diffusion system describing Ca2+ ligand buffering and diffusion in experimentally-derived rodent ventricular myocyte geometries. Results reveal the important role for mobile and stationary Ca2+ buffers, including Ca2+ indicator dye. We found that the alterations in Ca2+-binding and dissociation rates of troponin C (TnC) and total TnC concentration modulate subcellular Ca2+ signals. Model predicts that reduced off-rate in whole troponin complex (TnC, TnI, TnT) versus reconstructed thin filaments (Tn, Tm, actin) alters cytosolic Ca2+ dynamics under control conditions or in disease-linked TnC mutations. The ultimate goal of these studies is to develop scalable methods and theories for integration of molecular-scale information into simulations of cellular-scale systems.
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Affiliation(s)
- Y Cheng
- Department of Bioengineering, University of California, San Diego, La Jolla, CA 92093, USA
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42
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Pinder JC, Taylor-Harris PM, Bennett PM, Carter E, Hayes NVL, King MDA, Holt MR, Maggs AM, Gascard P, Baines AJ. Isoforms of protein 4.1 are differentially distributed in heart muscle cells: relation of 4.1R and 4.1G to components of the Ca2+ homeostasis system. Exp Cell Res 2012; 318:1467-79. [PMID: 22429617 DOI: 10.1016/j.yexcr.2012.03.003] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2010] [Revised: 03/01/2012] [Accepted: 03/02/2012] [Indexed: 11/30/2022]
Abstract
The 4.1 proteins are cytoskeletal adaptor proteins that are linked to the control of mechanical stability of certain membranes and to the cellular accumulation and cell surface display of diverse transmembrane proteins. One of the four mammalian 4.1 proteins, 4.1R (80 kDa/120 kDa isoforms), has recently been shown to be required for the normal operation of several ion transporters in the heart (Stagg MA et al. Circ Res, 2008; 103: 855-863). The other three (4.1G, 4.1N and 4.1B) are largely uncharacterised in the heart. Here, we use specific antibodies to characterise their expression, distribution and novel activities in the left ventricle. We detected 4.1R, 4.1G and 4.1N by immunofluorescence and immunoblotting, but not 4.1B. Only one splice variant of 4.1N and 4.1G was seen whereas there are several forms of 4.1R. 4.1N, like 4.1R, was present in intercalated discs, but unlike 4.1R, it was not localised at the lateral plasma membrane. Both 4.1R and 4.1N were in internal structures that, at the level of resolution of the light microscope, were close to the Z-disc (possibly T-tubules). 4.1G was also in intracellular structures, some of which were coincident with sarcoplasmic reticulum. 4.1G existed in an immunoprecipitable complex with spectrin and SERCA2. 80 kDa 4.1R was present in subcellular fractions enriched in intercalated discs, in a complex resistant to solubilization under non-denaturing conditions. At the intercalated disc 4.1R does not colocalise with the adherens junction protein, β-catenin, but does overlap with the other plasma membrane signalling proteins, the Na/K-ATPase and the Na/Ca exchanger NCX1. We conclude that isoforms of 4.1 proteins are differentially compartmentalised in the heart, and that they form specific complexes with proteins central to cardiomyocyte Ca(2+) metabolism.
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Affiliation(s)
- Jennifer C Pinder
- King's College London, Randall Division of Cell and Molecular Biophysics, New Hunt's House, Guy's Campus, London SE1 1UL, UK
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ter Keurs HEDJ. The interaction of Ca2+ with sarcomeric proteins: role in function and dysfunction of the heart. Am J Physiol Heart Circ Physiol 2012; 302:H38-50. [PMID: 22021327 PMCID: PMC3334233 DOI: 10.1152/ajpheart.00219.2011] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/04/2011] [Accepted: 10/11/2011] [Indexed: 12/28/2022]
Abstract
The hallmarks of the normal heartbeat are both rapid onset of contraction and rapid relaxation as well as an inotropic response to both increased end-diastolic volume and increased heart rate. At the microscopic level, Ca(2+) plays a crucial role in normal cardiac contraction. This paper reviews the cycle of Ca(2+) fluxes during the normal heartbeat, which underlie the coupling between excitation and contraction and permit a highly synchronized action of cardiac sarcomeres. Length dependence of the response of the regulatory sarcomeric proteins mediates the Frank-Starling Law of the heart. However, Ca(2+) transport may go astray in heart disease such as in congestive heart failure, and both jeopardize systole and diastole and triggering arrhythmias. The interaction between weak and strong segments in nonuniform cardiac muscle allows partial preservation of force of contraction but may further lead to mechanoelectric feedback or reverse excitation-contraction coupling mediating an early diastolic Ca(2+) transient caused by the rapid force decrease during the relaxation phase. These rapid force changes in nonuniform muscle may cause arrhythmogenic Ca(2+) waves to propagate by the activation of neighboring sarcoplasmic reticulum by diffusing Ca(2+) ions.
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44
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Winslow RL, Greenstein JL. Cardiac myocytes and local signaling in nano-domains. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2011; 107:48-59. [PMID: 21718716 PMCID: PMC3190073 DOI: 10.1016/j.pbiomolbio.2011.06.005] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Received: 06/14/2011] [Accepted: 06/14/2011] [Indexed: 10/18/2022]
Abstract
It is well known that calcium-induced calcium-release in cardiac myocytes takes place in spatially restricted regions known as dyads, where discrete patches of junctional sarcoplasmic reticulum tightly associate with the t-tubule membrane. The dimensions of a dyad are so small that it contains only a few Ca²⁺ ions at any given time. Ca²⁺ signaling in the dyad is therefore noisy, and dominated by the Brownian motion of Ca²⁺ ions in a potential field. Remarkably, from this complexity emerges the integrated behavior of the myocyte in which, under normal conditions, precise control of Ca²⁺ release and muscle contraction is maintained over the life of the cell. This is but one example of how signal processing within the cardiac myocyte and other cells often occurs in small "nano-domains" where proteins and protein complexes interact at spatial dimensions on the order of ∼1-10 nm and at time-scales on the order of nanoseconds to perform the functions of the cell. In this article, we will review several examples of local signaling in nano-domains, how it contributes to the integrative behavior of the cardiac myocyte, and present computational methods for modeling signal processing within these domains across differing spatio-temporal scales.
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Affiliation(s)
- Raimond L Winslow
- The Institute for Computational Medicine & Department of Biomedical Engineering, The Johns Hopkins University, School of Medicine & Whiting School of Engineering, Baltimore, MD 21218, USA.
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45
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Connelly KA, Advani A, Kim S, Advani SL, Zhang M, White KE, Kim YM, Parker C, Thai K, Krum H, Kelly DJ, Gilbert RE. The cardiac (pro)renin receptor is primarily expressed in myocyte transverse tubules and is increased in experimental diabetic cardiomyopathy. J Hypertens 2011; 29:1175-84. [PMID: 21505358 DOI: 10.1097/hjh.0b013e3283462674] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
BACKGROUND The pro(renin) receptor is a 350 amino acid transmembrane protein, that on ligand binding, increases the catalytic efficiency of angiotensinogen cleavage by both prorenin and renin, augmenting angiotensin I formation at the cell surface. While implicated in a broad range of diseases, studies to date have focused on the kidney, particularly in the diabetic context. We sought to examine the site-specific expression of the pro(renin) receptor within the heart. METHODS Using confocal microscopy, site-specific markers and transmission electron microscopy we assessed the location of the pro(renin) receptor in the heart at both cellular/sub-cellular levels. We assessed pro(renin) receptor expression in the setting of disease and blockade of the renin-angiotensin system, using the TGR[m(Ren2)-27] model of diabetic cardiomyopathy and the direct renin inhibitor, aliskiren. RESULTS The pro(renin) receptor was found predominantly at the Z-disc and dyad of cardiac myocytes coinciding closely with the distributions of the vacuolar H⁺-ATPase and ryanodine receptor, known to be located within T-tubules and the sarcoplasmic reticulum's terminal cisternae, respectively. Pro(renin) receptor mRNA/protein abundance were increased ∼3-fold in the hearts of diabetic rats in association with diastolic dysfunction, myocyte hypertrophy and interstitial fibrosis (all P < 0.01). Direct renin inhibition reduced cardiac pro(renin) receptor expression in association with improved cardiac structure/function (all P < 0.05). CONCLUSION Together, these findings are consistent with the notion that the pro(renin) receptor is a component of the vacuolar H⁺-ATPase, and that like the latter, is increased in the setting of cardiac stress and lowered by the administration of an ostensibly cardioprotective agent.
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Affiliation(s)
- Kim A Connelly
- Keenan Research Centre in the Li Ka Shing Knowledge Institute, St. Michael's Hospital and University of Toronto, Toronto, Canada
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Kemi OJ, Hoydal MA, Macquaide N, Haram PM, Koch LG, Britton SL, Ellingsen O, Smith GL, Wisloff U. The effect of exercise training on transverse tubules in normal, remodeled, and reverse remodeled hearts. J Cell Physiol 2011; 226:2235-43. [PMID: 21660947 PMCID: PMC3096693 DOI: 10.1002/jcp.22559] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
The response of transverse (T)-tubules to exercise training in health and disease remains unclear. Therefore, we studied the effect of exercise training on the density and spacing of left ventricle cardiomyocyte T-tubules in normal and remodeled hearts that associate with detubulation, by confocal laser scanning microscopy. First, exercise training in normal rats increased cardiomyocyte volume by 16% (P < 0.01), with preserved T-tubule density. Thus, the T-tubules adapted to the physiologic hypertrophy. Next, we studied T-tubules in a rat model of metabolic syndrome with pressure overload-induced concentric left ventricle hypertrophy, evidenced by 15% (P < 0.01) increased cardiomyocyte size. These rats had only 85% (P < 0.01) of the T-tubule density of control rats. Exercise training further increased cardiomyocyte volume by 8% (P < 0.01); half to that in control rats, but the T-tubule density remained unchanged. Finally, post-myocardial infarction heart failure induced severe cardiac pathology, with a 70% (P < 0.01) increased cardiomyocyte volume that included both eccentric and concentric hypertrophy and 55% (P < 0.01) reduced T-tubule density. Exercise training reversed 50% (P < 0.01) of the pathologic hypertrophy, whereas the T-tubule density increased by 40% (P < 0.05) compared to sedentary heart failure, but remained at 60% of normal hearts (P < 0.01). Physiologic hypertrophy associated with conserved T-tubule spacing (~1.8-1.9 µm), whereas in pathologic hypertrophy, T-tubules appeared disorganized without regular spacing. In conclusion, cardiomyocytes maintain the relative T-tubule density during physiologic hypertrophy and after mild concentric pathologic hypertrophy, whereas after severe pathologic remodeling with a substantial loss of T-tubules; exercise training reverses the remodeling and partly corrects the T-tubule density.
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Affiliation(s)
- Ole J Kemi
- Institute of Cardiovascular and Medical Sciences, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, UK.
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Pott C, Eckardt L, Goldhaber JI. Triple threat: the Na+/Ca2+ exchanger in the pathophysiology of cardiac arrhythmia, ischemia and heart failure. Curr Drug Targets 2011; 12:737-47. [PMID: 21291388 PMCID: PMC4406235 DOI: 10.2174/138945011795378559] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2010] [Accepted: 08/30/2010] [Indexed: 02/02/2023]
Abstract
The Na(+)/Ca(2+) exchanger (NCX) is the main Ca(2+) extrusion mechanism of the cardiac myocyte and thus is crucial for maintaining Ca(2+) homeostasis. It is involved in the regulation of several parameters of cardiac excitation contraction coupling, such as cytosolic Ca(2+) concentration, repolarization and contractility. Increased NCX activity has been identified as a mechanism promoting heart failure, cardiac ischemia and arrhythmia. Transgenic mice as well as pharmacological interventions have been used to support the idea of using NCX inhibition as a future pharmacological strategy to treat cardiovascular disease.
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Affiliation(s)
- Christian Pott
- University Hospital of Muenster, Department of Cardiology and Angiology, Albert-Schweitzer-Str. 33, 48149 Muenster, Germany.
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48
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Greenstein JL, Winslow RL. Integrative systems models of cardiac excitation-contraction coupling. Circ Res 2011; 108:70-84. [PMID: 21212390 PMCID: PMC3074965 DOI: 10.1161/circresaha.110.223578] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/30/2010] [Accepted: 10/18/2010] [Indexed: 11/16/2022]
Abstract
Excitation-contraction coupling in the cardiac myocyte is mediated by a number of highly integrated mechanisms of intracellular Ca²(+) transport. The complexity and integrative nature of heart cell electrophysiology and Ca²(+) cycling has led to an evolution of computational models that have played a crucial role in shaping our understanding of heart function. An important emerging theme in systems biology is that the detailed nature of local signaling events, such as those that occur in the cardiac dyad, have important consequences at higher biological scales. Multiscale modeling techniques have revealed many mechanistic links between microscale events, such as Ca²(+) binding to a channel protein, and macroscale phenomena, such as excitation-contraction coupling gain. Here, we review experimentally based multiscale computational models of excitation-contraction coupling and the insights that have been gained through their application.
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Affiliation(s)
- Joseph L Greenstein
- Center for Cardiovascular Bioinformatics and Modeling, Whitaker Biomedical Engineering Institute, The Johns Hopkins University, Baltimore, MD, USA
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Chase A, Orchard CH. Ca efflux via the sarcolemmal Ca ATPase occurs only in the t-tubules of rat ventricular myocytes. J Mol Cell Cardiol 2011; 50:187-93. [PMID: 20971118 DOI: 10.1016/j.yjmcc.2010.10.012] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/13/2010] [Revised: 10/07/2010] [Accepted: 10/08/2010] [Indexed: 10/18/2022]
Abstract
The transverse (t-) tubule network is an important site for Ca influx and release during excitation-contraction coupling in cardiac ventricular myocytes; however, its role in Ca extrusion is less clear. The present study was designed to investigate the relative contributions of Ca extrusion pathways across the t-tubule and surface membranes. Ventricular myocytes were isolated from the hearts of adult male Wistar rats and detubulated using formamide. Intracellular Ca was monitored using fluo-3 and confocal microscopy. Caffeine (20 mmol/L) was used to induce SR Ca release; carboxyeosin (20 μmol/L) and nickel (10 mmol/L) were used to inhibit the sarcolemmal Ca ATPase and Na/Ca exchanger (NCX) respectively. Carboxyeosin decreased the rate constant of decay of the caffeine-induced Ca transient in control cells, but had no effect in detubulated cells, suggesting that Ca extrusion via the Ca ATPase occurs only across the t-tubule membrane. However nickel decreased the rate constant of the caffeine-induced Ca transient in control and detubulated cells, although its effect was greater in control cells, suggesting that Ca extrusion via NCX occurs across the surface and t-tubule membranes. The PKA inhibitor H-89 (10 μmol/L) was used to investigate the role of basal PKA activity in Ca extrusion; H-89 appeared to have no effect on Ca extrusion via the Ca ATPase, but reduced Ca extrusion via NCX at the t-tubules but not the surface membrane. Thus it appears that Ca extrusion via the sarcolemmal Ca ATPase occurs only at the t-tubules, and is not regulated by basal PKA activity, while Ca extrusion via NCX occurs across both the surface and t-tubule membranes, but predominantly across the t-tubule membrane due, in part, to localised stimulation of NCX by PKA at the t-tubules. This may be important in heart disease, in which changes in t-tubule structure and protein phosphorylation occur.
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Affiliation(s)
- Anabelle Chase
- Department of Physiology and Pharmacology, Faculty of Medical and Veterinary Sciences, University of Bristol, University Walk, Bristol BS8 1TD, UK
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Neco P, Rose B, Huynh N, Zhang R, Bridge JHB, Philipson KD, Goldhaber JI. Sodium-calcium exchange is essential for effective triggering of calcium release in mouse heart. Biophys J 2010; 99:755-64. [PMID: 20682252 DOI: 10.1016/j.bpj.2010.04.071] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2009] [Revised: 03/26/2010] [Accepted: 04/30/2010] [Indexed: 11/30/2022] Open
Abstract
In cardiac myocytes, excitation-contraction coupling depends upon sarcoplasmic reticular Ca2+ release triggered by Ca2+ influx through L-type Ca2+ channels. Although Na+-Ca2+ exchange (NCX) is essential for Ca2+ extrusion, its participation in the trigger process of excitation-contraction coupling is controversial. To investigate the role of NCX in triggering, we examined Ca2+ sparks in ventricular cardiomyocytes isolated from wild-type (WT) and cardiac-specific NCX knockout (KO) mice. Myocytes from young NCX KO mice are known to exhibit normal resting cytosolic Ca2+ and normal Ca2+ transients despite reduced L-type Ca2+ current. We loaded myocytes with fluo-3 to image Ca2+ sparks using confocal microscopy in line-scan mode. The frequency of spontaneous Ca2+ sparks was reduced in KO myocytes compared with WT. However, spark amplitude and width were increased in KO mice. Permeabilizing the myocytes with saponin eliminated differences between spontaneous sparks in WT and KO mice. These results suggest that sarcolemmal processes are responsible for the reduced spark frequency and increased spark width and amplitude in KO mice. When myocytes were loaded with 1 mM fluo-3 and 3 mM EGTA via the patch pipette to buffer diadic cleft Ca2+, the number of sparks triggered by action potentials was reduced by 60% in KO cells compared to WT cells, despite similar SR Ca2+ content in both cell types. When EGTA was omitted from the pipette solution, the number of sparks triggered in KO and WT myocytes was similar. Although the number of sparks was restored in KO cells, Ca2+ release was asynchronous. These results suggest that high subsarcolemmal Ca2+ is required to ensure synchronous triggering with short spark latency in the absence of NCX. In WT mice, high subsarcolemmal Ca2+ is not required for synchronous triggering, because NCX is capable of priming the diadic cleft with sufficient Ca2+ for normal triggering, even when subsarcolemmal Ca(2+) is lowered by EGTA. Thus, reducing subsarcolemmal Ca2+ with EGTA in NCX KO mice reveals the dependence of Ca2+ release on NCX.
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Affiliation(s)
- Patricia Neco
- Departments of Medicine (Cardiology) and Physiology and the Cardiovascular Research Laboratories, David Geffen School of Medicine at UCLA, Los Angeles, California, USA
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