Adaptive seasonal changes in cardiac electrical activity of ectothermic vertebrates

One of the problems which ectothermic animals have to face during the fall of the ambient temperature is the negative change in parameters of the cardiac electrical activity leading to the decrease in the cardiac output. This is crucially important for those ectotherms which remain highly active during the cold season. The present review discusses the known physiological mechanisms which allow the ectothermic vertebrates, primarily various fish species, to reduce at least partially the cold-induced changes of cardiac electrical activity and to maintain the functional capacity of the heart at sufficient level for the active life during the winter. These mechanisms include the increase of density and/or changes in steady-state activation and inactivation parameters of ionic currents in cardiac myocytes. The acute temperature-dependent changes in ionic currents and electrical activity are also discussed, including the temperature effects on the excitability of cardiac myocytes.