The proposed research plan will focus on the action of acetyl glyceryl ether phosphorylcholine (AGEPC, platelet activating factor), a potent vasoactive/inflammatory mediator, on calcium homeostasis in vascular endothelium. Biochemical and cellular mechanisms of AGEPC-specific effects on calcium movements (45Ca2+ flux) and on cytosolic free calcium concentration (quin 2, calcium-sensitive fluorescent dye) will be studied in cultured endothelial cells isolated from different vessel types and species. Specific aims include: 1) defining the temporal- and concentration-dependent patterns of AGEPC-induced changes in endothelial calcium homeostasis; 2) identifying the sources and sinks of cellular calcium involved in the action of AGEPC; 3) characterizing agonist-induced desensitization of AGEPC effects and the potential interactions of AGEPC and other vasoactive/inflammatory substances in endothelial calcium homeostasis; 4) defining the effects of different calcium antagonists in this system; and 5) examining the role of cyclic nucleotides (cyclic AMP, cyclic GMP) and cyclooxygenase products (prostacyclin) in endothelial calcium homeostasis. These studies should provide new information on the cellular mechanisms of AGEPC action on vascular endothelium, a process relevant to acute and chronic inflammation. In addition, these studies may also provide new insights into the role of altered endothelial calcium homeostasis in the pathogenesis of more complex vascular diseases, such as thrombosis and atherosclerosis.