The overall objective of this revised proposal is to elucidate the molecular mechanisms coupling electrical excitability of ?-cells to glucose-induced insulin secretion (GSIS) in normal and diabetic states. We seek to test hypotheses concerning the role of voltage- dependent K+ (Kv) channels in regulating electrical activity and changes in intracellular free Ca2+ concentration ([Ca2+]i) that triggers GSIS. Once metabolism leads to closure of KATP channels generating action potentials (APs), Kv channels serve a distinct role in repolarizing the ?-cell membrane, resulting in Ca2+ transients necessary for insulin secretion. Incretin agonists used to treat diabetes reduce Kv currents by a PKA- dependent mechanism, but the identity of the Kv channels involved remains undefined. The Kv channel Kv2.1 is the predominant Kv channel in ?-cells, thought to be a critical channel for ?-cell membrane repolarization. We found that Kv2.1-/- mice, a new knockout model, exhibit abnormal glucose homeostasis with a significant resting hypoglycemia and increased insulin secretion in response to physiological steps in glucose concentration. The islets have wide and aberrant action potentials (APs). Surprisingly the Kv2.1-/- islets remain sensitive to tetraethylammonium, a blocker of Kv channels and Ca2+-activated K+ channels (KCa). These results reveal that other K+ channels participate in membrane repolarization and generation of APs, and could be targets for regulation. We propose to study the properties of these Kv currents not previously studied in normal mouse models in wild type and Kv2.1-/- mice with the following two specific aims:
Aim 1. To define mechanisms underlying regulation of insulin secretion and calcium signaling by Kv channels.
Aim 2. To define the molecular identity of repolarizing K+ channels expressed in ?-cells and understand the role they play in ?-cell excitation-secretion coupling. The results of these studies will enhance our understanding of the importance of Kv channels in insulin secretion and their role in the pathogenesis and potential treatment of diabetes.
Diabetes Mellitus is an important health problem, caused by abnormal insulin secretion relative to the degree of insulin resistance leading to numerous complications. This project addresses important biophysical aspects of the regulation of insulin secretion focusing on how potassium ion movement in and out of the cell controls insulin secretion.
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