Critical role of bicarbonate and bicarbonate transporters in cardiac function

Figure 1 Relative expression levels of the major Cl^-/HCO₃^- exchangers and Na⁺/HCO₃^- cotransporters in mouse heart. RPKM values ± SE as determined by RNA Seq analysis (see Table 1 legend) are shown for the most abundant known HCO₃^- transporters in wild-type FVB/N mouse hearts (n = 4). Note the difference in scale for AE3 and the other transporters.

Figure 2 Isolated myocytes exhibit greater contractility in CO₂/HCO₃^- buffer than in HEPES buffer. Ventricular myocytes from rat hearts were enzymatically dissociated using Langendorff perfusion[104] and myocyte mechanics were analyzed at room temperature (24 °C), with stimulation at 0.5 Hz as described previously[107]. Myocytes were switched between HEPES-buffered Tyrode’s solution (in mmol/L: NaCl 140, KCl 5.4, MgCl₂ 1, CaCl₂ 1.8, glucose 10, and Na-HEPES 5; pH = 7.4; bubbled with 100% O₂) and HCO₃^--buffered Krebs solution (in mmol/L: NaCl 120, NaHCO₃^- 25, KCl 4.2, KH₂PO₄ 1.2, MgCl₂ 1, CaCl₂ 1.8, and glucose 10; pH = 7.4 when bubbled with 95% O₂ and 5% CO₂). A: Representative contraction tracing of a myocyte bathed in HEPES buffer, then switched to HCO₃^- buffer, and then returned to HEPES buffer; the lower tracings show an expanded scale for the indicated (a-d) time points. The lower panels show the time course of fractional shortening (B) and average fractional shortening (C) of myocytes (n = 19) in HEPES buffer and then switched to HCO₃^--containing buffer. Experiments were performed using myocytes from 3 hearts and statistical analysis was conducted using a paired t-test. Values are means ± SE.

Figure 3 Ca²⁺ transient analysis in isolated rat myocytes bathed in CO₂/HCO₃^- buffer and in HEPES buffer. For recording of Ca²⁺ transients, isolated ventricular myocytes were loaded with fluo-4 acetoxymethyl ester (5 μmol/L, Molecular Probes, Eugene, OR) and activated with field stimulation at 0.5 Hz. Fluorescence signals were measured using a Nikon TE 2000 microscope and an InCyt Standard PM photometry system (Intracellular Imaging, Cincinnati, OH) as described previously[104]. A: Representative Ca²⁺ transients in HEPES and HCO₃^--containing buffers; B: Average Ca²⁺ transient (CaT) amplitudes and tau values, a measure of the rate of decay of the Ca²⁺ transient in HEPES and HCO₃^--containing buffers (n = 12). The same cells were imaged in both buffers. Myocytes were from the same preparations used in Figure 2, with statistical analyses performed using a paired t-test. No significant differences were observed.