Cardiac adaptations to low temperature in non-polar teleost fish

Abstract

Acclimation of teleost fish to low temperature results in a number of well-characterized adaptive responses in skeletal muscle. Our understanding of the response of cardiac muscle to such a challenge though is still poorly understood. It is considered of interest to learn more about the impact of chronic low temperature exposure on the cardiac response since the heart is required to support other tissues through the delivery of oxygen and metabolic fuels and this system may be a useful model in which to identify loci of cardiac plasticity. An overview of the available data reveals a number of fundamental responses. These include an increase in heart mass, an increase in maximal contraction frequency, an increase in complex lipid biosynthesis, and an increase in aerobic-based fatty acid metabolism. Two different strategies seem to emerge and lead to working hypotheses. As one example, rainbow trout develop larger hearts which may lead to enhanced stroke volume. The net accretion of protein is associated with either a more effective use of the available protein synthetic machinery and/or a decrease in protein degradation. The net accretion of lipid is associated with an increased rate of biosynthesis. Energy metabolism at low temperature appears to be much more dependent upon the oxidation of fatty acids. As another example, perch acclimated to low temperature show enhanced maximal rates of contraction which may be associated with increase in the volume of sarcoplasmic reticulum. The metabolic processes necessary to supply ATP appear quite adequate and require no further expansion as evidenced by constant mitochondrial volume density and activity of mitochondrial marker enzymes. The data however, in both cases are fragmentary and call for comprehensive studies on selected species. © 1996 Wiley-Liss, Inc.