Thermal acclimation confers no tolerance to acute temperature change in cardiac myocytes from bluefin tuna

Abstract

Pacific bluefin tuna, Thunnus orientalis, make extensive horizontal and vertical migrations where they inhabit a broad range of thermal niches. Although tuna are capable of conserving metabolic heat, the hearts of these fishes operate at near ambient water temperatures, and must therefore be able to function at a broad range of temperatures.Study objectiveto investigate the effects of thermal acclimation and acute temperature change on aspects of sarcolemmal and intracellular calcium cycling in isolated cardiac myocytes from the Pacific bluefin tuna.MethodsAtrial and ventricular myocytes were isolated from bluefin tuna acclimated to either 15 or 23 °C, and the effect of experimental temperature (15, 19 and 23 °C) on the sarcoplasmic reticulum load (SRload) and L‐type calcium channel density (ICa) was assessed using whole‐cell voltage‐clamp.ResultsThermal acclimation has little effect on ICa or the ability of the SR to accumulate calcium. Acute reductions in temperature significantly decreased both ICa and SRload in atrial and ventricular myocytes from both acclimation temperatures.ConclusionsAcute reductions in temperature reduce calcium flux both across the sarcolemmal membrane and through the SR. This will place a significant burden on the heart of the diving bluefin tuna and may limit the amount of time these animals can spend in cold waters.