The broad and long-term objectives of this diabetes-related proposal are to advance the investigator's understanding of the control of insulin secretion and the mechanism involved in such control. Specifically, the work will characterize the properties of galanin, a recently discovered peptide, which potently inhibits the release of insulin form pancreatic beta-cells. The effects of galanin on insulin secretion stimulated by glucose, amino acids, hormones and other important physiological and pharmacological agents will be studied. Rat pancreatic islets will be used under conditions of both static incubation and perifusion, as well as the RINm5F beta-cell line and other cell lines as appropriate. Evidence is available that galanin has four distinct actions on beta-cells, and the importance of each to the overall physiological inhibition will be the plasma membrane with consequent hyperpolarization of the membrane and preliminary results), 3) inhibition of adenylate cyclase and 4) an apparent """"""""distal"""""""" inhibitory effect in stimulus-secretion coupling which may be close to the final exocytotic events. Studies will be performed on galanin binding to cells and membranes to help understand galanin receptor function. As the effects of galanin are sensitive to pertussis toxin, G proteins in the beta-cell will be characterized and their interaction with the galanin receptor explored. Additionally, the investigators, plan to determine which G proteins are involved in the actions of galanin, and in the actions of other inhibitors of insulin release. These goals will be accomplished by the use of specific antibodies against the G proteins and newer techniques involving ADP ribosylation. Specific studies will be performed to understand the mechanisms underlying the four actions of galanin. The possibility that galanin induces supersensitivity of adenylate cyclase will be explored. By studying the effect of galanin to inhibit insulin secretion stimulated by guanylnucleotides in permeabilized beta-cells, it is anticipated that valuable information will be gained as to the final mechanisms of exocytosis. Finally, the findings with galanin will be compared and contrasted with the effects of other somatostatin, alpha 2-adrenergic agents and prostaglandins in order to seek for a common mechanism, or site, of action. The information gained should advance the investigators knowledge of the mechanisms and control of insulin secretion by the beta-cells.
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