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Am J Physiol Regul Integr Comp Physiol 278: R1535-R1544, 2000;
0363-6119/00 $5.00
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Vol. 278, Issue 6, R1535-R1544, June 2000

Effects of temperature and calcium availability on ventricular myocardium from rainbow trout

Mary D. Coyne1, Catherine S. Kim2, John S. Cameron1, and Judith K. Gwathmey2

1 Department of Biological Sciences, Wellesley College, Wellesley 02481-8203, and 2 Institute for Cardiovascular Disease and Muscle Research, Cambridge, Massachusetts 02138

We studied the mechanical and electrophysiological properties of ventricular myocardium from rainbow trout (Oncorhynchus mykiss) in vitro at 4, 10, and 18°C from fish acclimated at 10°C. Temperature alone did not significantly alter the contractile force of the myocardium, but the time to peak tension and time to 80% relaxation were prolonged at 4°C and shortened at 18°C. The duration of the action potential was also prolonged at 4°C and progressively shortened at higher temperatures. An alteration of the stimulation frequency did not affect contraction amplitude at any temperature. Calcium influx via L-type calcium channels was increased by raising extracellular calcium concentration ([Ca2+]o) or including Bay K 8644 (Bay K) and isoproterenol in the bathing medium. These treatments significantly enhanced the contractile force at all temperatures. Calcium channel blockers had a reverse-negative inotropic effect. Unexpectedly, the duration of the action potential at 10°C was shortened as [Ca2+]o increased. However, Bay K prolonged the plateau phase at 4°C. Caffeine, which promotes the release of sarcoplasmic reticulum (SR) calcium, increased contractile force eightfold at all three temperatures, but the SR blocker ryanodine was only inhibitory at 4°C. Our results suggest that contractile force in ventricular myocardium from Oncorhynchus mykiss is primarily regulated by sarcolemmal calcium influx and that ventricular contractility is maintained during exposure to a wide range of temperatures.

excitation-contraction coupling; calcium; myocardium; teleost


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