The Effect of Thermal Acclimation on Action Potentials and Sarcolemmal K Channels from Pacific Bluefin Tuna Cardiomyocytes

To sustain cardiac muscle contractility relatively independent of temperature, some fish species are capable of temporarily altering excitation-contraction (E-C) coupling processes to meet the demands of their environment. The Pacific bluefin tuna, Thunnus orientalis, is a partially endothermic fish that inhabits a wide range of thermal niches. The present study examined the effects of temperature and thermal acclimation on sarcolemmal K + currents and their role in action potential (AP) generation in bluefin tuna cardiomyocytes. Atrial and ventricular myocytes were enzymatically isolated from cold-(14 o C) and warm-(24 o C) acclimated bluefin tuna. AP's and current-voltage relations of K + channels were measured using the whole-cell current and voltage clamp techniques, respectively. Data were collected either at the cardiomyocytes' respective acclimation temperature of 14 or 24ºC or at a common test temperature of 19ºC (to reveal the effects of acclimation). AP duration (APD) was prolonged in cold-acclimated (CA) cardiomyocytes tested at 14 o C compared to 19 o C and in warm-acclimated (WA) cardiomyocytes tested at 19 o C compared with 24 o C. This effect was mirrored by a decrease in the density of the delayed rectifier current (I Kr), while the density of the background inward rectifier current (I K1) was unchanged. When CA and WA