This renewal application of an award in the third and final year aims to elucidate the roles of repolarizing delayed rectifier K channels (Kv) in pancreatic B-cell excitation-secretion coupling, specifically examining electrical activity, (Ca2+)i, and insulin secretion. Major goals of the first funding period have been met with the conclusion that Kv1 channels are unlikely to play a major role in the B-cell. Significant progress included demonstration of Kv2 and Kv3 expression in B-cells and insulinoma cells. In the next period we will test th hypothesis that regulation of membrane repolarization by Kv2 and Kv3 govern B-cell glucose responsiveness through these interlocking Specific Aims:
Specific Aim 1 : To define the factors that influence the expression of Kv channels in the B-cells of transgenic mice. Dominant negative transgenics for Kv2 and Kv3 will be compared with similar constructs that suppress related Ca2+-activated K channels. Factors that determine transgenic and endogenous Kv channel expression will be defined.
Specific Aim 2 : To define the effects of K isoform suppression on glucose tolerance and insulin secretion. Glucose induce secretion will be studied in whole animals, the isolated perfused pancreas, an perifused islets and compared with antagonist blockade of Kv channels. These experiments, in combination with those of the next aim, will test the hypothesis that Kv regulation of membrane repolarization is functionally related to insulin secretion, and will determine whether alterations in B-cell excitability lead to compensatory changes or hyperinsulinemia.
Specific Aim 3 :_To define the effects of Kv isoform suppression on whole cell currents, electrical activity and (Ca2+)i transients in B-cells and islets, and correlat them with changes in insulin secretion. The B-cells of delayed rectifier-deficient mice are predicted to have slowed repolarization, increase excitability, and enhanced (Ca2+)i transients. The amplitude and pharmacology of the outward currents and the characteristics of electrical bursting will be determined. Experiments performed under these specific aims will allow us to (1) test the overall hypothesis that Kv channels play a key role in membrane repolarization; (2) test the degree of coupling of glucose stimulation to membrane events and insulin secretion in vivo models and (3) define the functional importance of specific delayed rectifier isoforms expressed in B-cells. The differences in sensitivities of these isoforms to Kv blockers may lead to the development of novel therapeutic approaches in NIDDM.
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