Cardiac thermal acclimation and adaption of the heart to extreme temperatures

An acute change in temperature has a significant effect on the contractile function of the heart. This is because of changes in the function of multiple cellular components including ion channels and transporters, metabolic enzymes and the contractile machinery. There are, however, multiple fish species that remain active in environments where temperature changes seasonally by at least 10°C, or that live in Antarctica where temperatures do not increase over 0°C. Being able to do so requires significant phenotypic plasticity/adaptation in the cardiovascular system of these species. Studies with e.g., rainbow trout and zebrafish demonstrate that thermal acclimation causes multiple changes to the heart thought to help maintain contractile function. This includes increased densities of ion channels in the sarcolemma, increased sensitivity of the myofilament to Ca2+, increased reliance on fatty acids for energy production, increased sensitivity to adrenergic stimulation and changes to the size and composition of the heart. Study of Antarctic notothenioid fish demonstrates that the hearts of these fish have a much larger relative chamber volume, that the blood of some species contains no hemoglobin and that the diameter of some blood vessels are significantly larger than that in temperature species. These adaptations are thought to help maintain cardiac function in the subzero temperatures of Antarctic waters.