Biological membranes play a critical role in cell function by controlling the flow of both materials (nutrients and waste products) and information (by determining to which chemical stimuli the cell is responsive) between the cell and its environment. Yet the physical state of these membranes is subject to perturbation by changes in temperature, and at cold temperatures, membrane constituents may, in actuality, 'freeze' - a condition not compatible with the maintenance of biological function. In poikilothermic animals (animals whose body temperature varies with environmental temperature), this problem is circumvented by a process of physiological adaptation which replaces membrane components formed at warm temperatures with more fluid ones at cold temperatures. In this way, membrane function can be maintained over a wide range of body temperatures. Thus cold-blooded animals are unique in being able to produce functionally equivalent membranes of different chemical composition at different growth temperatures. For this reason, the rainbow trout is an ideal model system in which to study the influence of membrane composition upon membrane function. Three aspects of the above general problem will be explored in the work proposed. One focus is to determine the extent to which temperature- induced changes in membrane lipid composition influence the ability of a cell to respond to hormonal stimulation. A second question is to determine the extent to which a cell may regulate membrane function by controlling the composition (primarily the pH) of the cytoplasmic compartment in which membranes function ?cold-blooded animals exhibit unique patterns of acid-base regulation as body temperature changes which permit this question to be addressed in a more straightforward manner than would be possible in a homeotherm!. Finally, studies will also be undertaken to identify the steps in membrane assembly that permit the membrane to be restructured as temperature changes. These studies will provide a better understanding of how the chemical composition of a membrane influences its function as well as indicating the types of structural modification effective in modulating specific membrane activities. Such results are of broad general significance because of the importance of membrane-mediated processes in such diverse functions as nutrient absorption by the intestine, excretion by the kidneys, and the responsiveness of many body cells to hormones.
