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

Abstract

Voltage-dependent (Kv) outward K ؉ currents repolarize ␤-cell action potentials during a glucose stimulus to limit Ca 2؉ entry and insulin secretion. Dominant-negative "knockout" of Kv2 family channels enhances glucose-stimulated insulin secretion. Here we show that a putative Kv2.1 antagonist (C-1) stimulates insulin secretion from MIN6 insulinoma cells in a glucose-and dosedependent manner while blocking voltage-dependent outward K ؉ currents. C-1-blocked recombinant Kv2.1-mediated currents more specifically than currents mediated by Kv1, -3, and -4 family channels (Kv1.4, 3.1, 4.2). Additionally, C-1 had little effect on currents recorded from MIN6 cells expressing a dominant-negative Kv2.1 ␣-subunit. The insulinotropic effect of acute Kv2.1 inhibition resulted from enhanced membrane depolarization and augmented intracellular Ca 2؉ responses to glucose. Immunohistochemical staining of mouse pancreas sections showed that expression of Kv2.1 correlated highly with insulin-containing ␤-cells, consistent with the ability of C-1 to block voltage-dependent outward K ؉ currents in isolated mouse ␤-cells. Antagonism of Kv2.1 in an ex vivo perfused mouse pancreas model enhanced first-and second-phase insulin secretion, whereas glucagon secretion was unaffected. The present study demonstrates that Kv2.1 is an important component of ␤-cell stimulus-secretion coupling, and a compound that enhances, but does not initiate, ␤-cell electrical activity by acting on Kv2

Voltage-dependent K+ channels are positive regulators of alpha cell action potential generation and glucagon secretion in mice and humans

“…This would be similar to the well-known effect of inhibiting beta cell Kv currents on insulin secretion, even with very high concentrations (20 mmol/l) of TEA [11,16,20]. We found that alpha cell Kv currents are inhibited by low millimolar levels of TEA and 4-aminopyridine.…”

“…Notably, we did not observe the TEA-resistant rapidly inactivating current component reported previously in isolated alpha cells [19] and alpha cells from intact islets [3]. In beta cells, inhibition of Kv currents with TEA augments insulin secretion in a glucose-dependent manner, since Kv channels contribute to action potential repolarisation [11,16,20]. Since alpha cells are electrically active at low glucose [3,4,21], we hypothesised that inhibition of Kv currents at low glucose concentrations should enhance glucagon secretion under this condition, due to action potential prolongation as is the case for beta cell insulin secretion.…”

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

“…Our observations suggest that Kv2.1 might represent one such channel. The PLA 2 product AA blocks the activity of these channels, and overexpression of iPLA 2 ␤ in insulinoma cells is associated with amplification of insulin secretion and suppression of Kv2.1 channel activity, which is consistent with previous observations that blockade of Kv2.1 activity by other means also results in increased insulin secretory responses (48,49).…”

“…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.…”

“…These results suggest that muscarinic receptor occupancy increases ␤-cell Kv current inactivation by iPLA 2 ␤-regulated mechanism(s), and this results in a shorter time to peak Kv current response. Phospholipase A 2 Regulates Delayed Rectifier Current Activity-iPLA 2 ␤ is expressed by islet ␤-cells from rats (29), humans (47), and mice (48), and by several insulinoma cell lines (31,38,39). Upon activation, iPLA 2 ␤ hydrolyzes the sn-2 substituent from phospholipids substrates, such as phosphatidylcholine, to yield a free fatty acid and a lysophospholipid, such as LPC (44,54,55).…”