The principal objective of this proposal is to test whether phospholipids, primarily the inositides, play a role in impulse propagation. As a first step, three nerve preparations, chosen for their widely differing levels of excitable membrane, will be used in experiments to determine if axolemmal membrane lipid metabolism is affected by electrical stimulation or membrane depolarization. Studies with different labeled precursors will delineate those steps of lipid metabolism that respond to electrical stimulation and/or membrane depolarization while followup quantitative EM autoradiographic studies will localize lipid changes (synthesis or breakdown) to excitable axon membranes. If lipid metabolism is responsive to nerve excitation, enzyme studies will address questions of how lipid metabolism of excitable membranes is regulated, with emphasis on the roles of calcium and enzyme lipid interaction, and how lipid changes could influence ion channel and/or pump activities. A separate approach to establish a relationship between excitability and lipids will be with animal models, Wallerian degeneration and diabetic neuropathy, displaying defective nerve conduction. These studies will serve to find out whether altertations in membrane lipids could underlie loss of excitability in these experimental models. The secondary objective of this proposal is to initiate studies that will lead to the establishment of a role for lipid metabolism in presynaptic nerve terminal function. As a first step, studies will address the localization of lipid metabolism to presynaptic terminals. Biochemical studies will be directed toward showing that lipid enzymes are components of secretory and endocytic vesicles. Autoradiographic studies, initially with tritiated inositol and choline, will determine whether the synthesis of lipids occurs in presynaptic terminals. These studies will be followed by others to find out whether lipid changes accompany neurotransmitter release and vesicle recycling. The possibility that calcium regulated lipolysis plays a role in terminal function will be examined.
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