The long-term objectives of this proposal are 1) to define the role of phospholipases C and A2 in nutrient, receptor-mediated, and sulfonylurea-mediated insulin secretion by the islets of Langerhans; and 2) to determine the role of de novo synthesis of diacylglycerol from glucose in insulin secretion and hyperglycemia, since in Type II diabetes mellitus there is a blunted insulin response to glucose. The first hypothesis is that phospholipases C and A2 which are located at the plasma membrane of the beta-cells of islets of Langerhans, have a major role in initiating and regulating insulin secretion. The second hypothesis is that de novo synthesis of lysophosphatidic acid, phosphatidic acid and diacylglycerol from glucose has a role in glucose-induced insulin secretion and in the adaptation of beta-cells to hyperglycemia in vitro.
Aim #1 is to define the molecular mechanism whereby glucose and other secretagogues activate phospholipase C in insulin secretion and to test the working hypothesis that glucose is recognized by a site on the beta cell which is coupled to phospholipase C.
Aim #2 will define and characterize the role of phospholipase A2 in insulin secretion and identify the molecular mechanisms whereby the different classes of secretagogues stimulate and regulate arachidonic acid accumulation.
Aim #3 will test the hypothesis that de novo synthesis of lysophosphatidic acid, phosphatidic acid and diacylglycerol from glucose has a major role in insulin secretion and in the adaptation of islets to hyperglycemia in vitro; the study will define at the molecular levels the pathways involved and their regulation.
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