Most fish species are ectothermic, i.e. their body temperature is directly determined and not significantly different from that of the water in which they live. This means that, for many temperate zone fish species, cell temperatures many vary seasonally by >20 degrees centigrade. Although decreasing temperature has a significant depressing effect upon biochemical reactions, many of these fish species display relatively constant biological activity at warm and cold temperatures, behavior which requires adaptive responses at the cellular and biochemical level. In particular, many adaptations of fishes to cold body temperature described to date are very similar to those shown by mammalian species (including man) to different physiological stimuli - e.g. endurance training. Dr. Sidell will utilize the more easily studied fish muscle system to : 1) define adaptations for metabolism of fatty fuels to support locomotion in fishes and how this system is influenced by changes in body temperature, and; 2) evaluate the adaptive significance of cold temperature-induced increases in intracellular fat content upon movement of oxygen through muscle. His experiments will focus upon striped bass (Morone saxatilis), a migratory fish of considerable economic importance. The investigator will utilize gas chromatography to determine how changes in body temperature affect the molecular composition of blood-borne and storage deposits of lipid (fat) fuels. The rate-limiting enzyme in breakdown of fatty fuels, carnitine long chain fatty acyltransferase, will be purified from aerobic muscle of striped bass. He will determine by enzyme kinetic analyses and metabolic experiments with isolated tissues which normally available fatty acid fuels are best metabolized at different temperatures. He will also quantify the concentrations of an intracellular fatty acid binding protein (FABP) in muscles of temperature acclimated fish. FABPs have been implicated in accelerating the intracellular movement of fatty acids. Titers of FABPs in tissues of thermally-acclimated animals will be correlated with the ability of these tissues to metabolize fats. FABP further will be purified and used to perform experiments that will directly resolve whether this protein can facilitate movement of fatty compounds in aqueous solution. Oxygen electrodes will be used to determine whether the presence of lipid droplets in cells (which accumulate in muscle at cold body temperature) can enhance the rate of diffusion of oxygen from capillaries to its site of cellular utilization, the mitochondria. Results from these studies will better define effects of seasonal cycles in temperature upon utilization of lipids which are important caloric resources in the aquatic environment. Findings may apply to the physiology of less easily studied muscle systems which show very similar treatment effects.
