9507226 Hazel The goal of the proposed research is to test the validity of a newly developed model of thermal adaptation in biological membranes of cold-blooded or poikilothermic animals that emphasizes the adaptive significance of conserving the dynamic phase behavior of a membrane, i.e., the ability to maintain and regulate such dynamic membrane properties as rates of endocytosis and fusion. Regulation of membrane fusion is a process fundamental to virtually all types of intracellular membrane traffic. The predictions of this model will be tested by studying several aspects of membrane structure and function in isolated plasma membranes of temperature-acclimated aquatic poikilotherms adapted to both cold (rainbow trout, Oncorhynchus mykiss, acclimated to 5 and 20 C) and warm (Tilapia mossambica, an African cichlid, acclimated to 20 and 35 C) waters and by comparing responses in these poikilotherms with comparable data collected from the homeothermic rat (body temperature of 37 C). The first objective of the proposed research is to determine the extent to which lipid phase boundaries are conserved at different body temperatures. The second objective is to determine the temperature sensitivity of dynamic membrane traffic in animals acclimated and adapted to different temperatures. Specifically, the temperature dependence of rates of both fluid- phase and receptor-mediated endocytosis, in addition to the rate of cholesterol transport from its site of synthesis in the ER to the plasma membrane, will be determined in isolated hepatocytes of trout, Tilapia and rat. The third objective is to determine the extent to which temperature acclimation/adaptation alters the fusogenic capacity of hepatic plasma membrane lipids. The significance of the proposed work lies in providing a better definition of those fundamental properties of a membrane that must be conserved in order for membrane function to be maintained at extremes of environmental temperature. ***
