Brief Article
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World J Diabetes. Jun 15, 2013; 4(3): 70-75
Published online Jun 15, 2013. doi: 10.4239/wjd.v4.i3.70
Caribbean maitotoxin elevates [Ca2+]i and activates non-selective cation channels in HIT-T15 cells
Xin-Zhong Lu, Robert Deckey, Guo-Liang Jiao, Hui-Feng Ren, Ming Li
Xin-Zhong Lu, Department of Pharmacology, University of South Alabama, Mobile, AL 36688, United States
Robert Deckey, Food and Drug Administration of United States, Mobile, AL 36609, United States
Guo-Liang Jiao, Hui-Feng Ren, Convelscent Hospital, Xingcheng 125100, Liaoning Province, China
Ming Li, Department of Physiology, Tulane University, New Orleans, LA 70112, United States
Author contributions: Lu XZ performed the majority of experiments; Deckey R, Jiao GL and Ren HF provided vital reagents and analytical tools and were also involved in editing the manuscript; Li M designed the study and wrote the manuscript.
Correspondence to: Dr. Ming Li, Department of Physiology, Tulane University, Health Sciences Center, 1430 Tulane Avenue, New Orleans, LA 70112, United States. mli@tulane.edu
Telephone: +1-504-9888207 Fax: +1-504-9882675
Received: December 21, 2012
Revised: March 28, 2013
Accepted: April 13, 2013
Published online: June 15, 2013
Processing time: 70 Days and 11.2 Hours
Abstract

AIM: To investigate the cytotoxic mechanism of caribbean maitotoxin (MTX-C) in mammalian cells.

METHODS: We used whole-cell patch-clamp techniques and fluorescence calcium imaging to determine the cellular toxic mechanisms of MTX-C in insulin secreting HIT-T15 cells, which is a system where the effects of MTX have been observed. HIT-T15 cells stably express L-type calcium current, making it a suitable model for this study. Using the fluorescence calcium indicator Indo-1 AM, we found that there is a profound increase in HIT-T15 intracellular free calcium 3 min after application of 200 nmol/L MTX-C.

RESULTS: About 3 min after perfusion of MTX-C, a gradual increase in free calcium concentration was observed. This elevation was sustained throughout the entire recording period. Application of MTX-C did not elicit the L-type calcium current, but large cationic currents appeared after applying MTX-C to the extracellular solution. The current-voltage relationship of the cation current is approximately linear within the voltage range from -60 to 50 mV, but flattened at voltages at -80 and -100 mV. These results indicate that MTX-C induces a non-voltage activated, inward current under normal physiological conditions, which by itself or through a secondary mechanism results in a large amount of cationic influx. The biophysical mechanism of MTX-C is different to its isoform, pacific maitotoxin (MTX-P), when the extracellular calcium is removed.

CONCLUSION: We conclude that MTX-C causes the opening of non-selective, non-voltage-activated ion channels, which elevates level of intracellular calcium concentration and leads to cellular toxicities.

Keywords: Maitotoxin, Calcium fluorescence, High voltage gated Ca2+ channels, Whole cell patch clamp, Insulin secreting cells

Core tip: The toxicity of maitotoxin is estimated to affect over 50000 people annually. Baracuda, snapper, grouper, jacks, and moray eel are particularly notorious for their potential to carry high toxin load. The symptoms of the toxicity include numbness of the perioral area and extremities, reversal of temperature sensation, muscle and joint aches, headache, itching tachycardia, hypertension, blurred vision, and paralysis. Our study aims to elucidate the cellular toxic mechanism of caribbean maitotoxin in mammalian cells. We conclude that it causes opening of non-selective, non-voltage activated ion channels, which elevates level of intracellular calcium concentration and leads to cellular toxicities.