Members of the Kv1 and Kv2 Voltage-Dependent K+ Channel Families Regulate Insulin Secretion

Abstract

In pancreatic beta-cells, voltage-dependent K(+) (Kv) channels are potential mediators of repolarization, closure of Ca(2+) channels, and limitation of insulin secretion. The specific Kv channels expressed in beta-cells and their contribution to the delayed rectifier current and regulation of insulin secretion in these cells are unclear. High-level protein expression and mRNA transcripts for Kv1.4, 1.6, and 2.1 were detected in rat islets and insulinoma cells. Inhibition of these channels with tetraethylammonium decreased I(DR) by approximately 85% and enhanced glucose-stimulated insulin secretion by 2- to 4-fold. Adenovirus-mediated expression of a C-terminal truncated Kv2.1 subunit, specifically eliminating Kv2 family currents, reduced delayed rectifier currents in these cells by 60-70% and enhanced glucose-stimulated insulin secretion from rat islets by 60%. Expression of a C-terminal truncated Kv1.4 subunit, abolishing Kv1 channel family currents, reduced delayed rectifier currents by approximately 25% and enhanced glucose-stimulated insulin secretion from rat islets by 40%. This study establishes that Kv2 and 1 channel homologs mediate the majority of repolarizing delayed rectifier current in rat beta-cells and that antagonism of Kv2.1 may prove to be a novel glucose-dependent therapeutic treatment for type 2 diabetes.

Modulation of the Pancreatic Islet β-Cell-delayed Rectifier Potassium Channel Kv2.1 by the Polyunsaturated Fatty Acid Arachidonate

“…Reducing Kv current prolongs stimulus-induced depolarization of the ␤-cell plasma membrane and thereby amplifies insulin secretion (46,48). This could account for the observations that overexpression of iPLA 2 ␤ in insulinoma cells is associated with both amplified insulin secretion (21) and reduced Kv2.1 channel activity (Fig.…”

“…To examine further effects of arachidonic acid on the activity of the Kv2.1 channel, which is the predominant delayed rectifier of ␤-cells (4,46), HEK cells expressing a Kv2.1-GFP construct (42) were studied (Fig. 1E) Arachidonic Acid Regulates Delayed Rectifier Currents in Both Rodent and Human Pancreatic Islet ␤-Cells-Because arachidonic acid affects the activity of Kv2.1 channels expressed in immortalized cell lines, we examined the possibility that similar effects would be observed with Kv currents in rodent and human primary ␤-cells.…”

“…1 and 2). Kv2.1 is the primary ␤-cell-delayed rectifier potassium channel (4,46), and ␤-cells incubated with AA secrete more insulin when stimulated than do cells incubated in the absence of AA (7). This response mimics the effects of Kv2.1 blockade under similar conditions (28,29).…”

Inhibition of Kv2.1 Voltage-dependent K+Channels in Pancreatic β-Cells Enhances Glucose-dependent Insulin Secretion

“…Indeed, previous studies show that the general voltage-dependent K ϩ (Kv) 1 and Ca 2ϩ -sensitive voltage-dependent K ϩ (K Ca ) channel antagonist tetraethylammonium (TEA) augments membrane depolarization (12,13), Ca 2ϩ influx (14), and insulin secretion (13,15) in a glucose-dependent manner. Recently, we have reported that dominant-negative knockout of Kv2 channels reduced outward K ϩ currents by 60 -70% in rat ␤-cells and HIT-T15 insulinoma cells and caused a doubling of the insulin secretion response of rat islets to glucose (16). Kv2.1 likely plays this regulatory role because its protein expression is high in insulin-secreting cells (16,17), and mRNA for Kv2.2, the only other Kv2 family ␣-subunit known to form functional channels, could not be detected by reverse transcription-PCR (16).…”

“…Recently, we have reported that dominant-negative knockout of Kv2 channels reduced outward K ϩ currents by 60 -70% in rat ␤-cells and HIT-T15 insulinoma cells and caused a doubling of the insulin secretion response of rat islets to glucose (16). Kv2.1 likely plays this regulatory role because its protein expression is high in insulin-secreting cells (16,17), and mRNA for Kv2.2, the only other Kv2 family ␣-subunit known to form functional channels, could not be detected by reverse transcription-PCR (16).…”