Inhibition of voltage-gated potassium channels mediates uncarboxylated osteocalcin-regulated insulin secretion in rat pancreatic β cells

Abstract

Insulin secretion from pancreatic β cells is important to maintain glucose homeostasis and is regulated by electrical activities. Uncarboxylated osteocalcin, a bone-derived protein, has been reported to regulate glucose metabolism by increasing insulin secretion, stimulating β cell proliferation and improving insulin sensitivity. But the underlying mechanisms of uncarboxylated osteocalcin-modulated insulin secretion remain unclear. In the present study, we investigated the relationship of uncarboxylated osteocalcin-regulated insulin secretion and voltage-gated potassium (KV) channels, voltage-gated calcium channels in rat β cells. Insulin secretion was measured by radioimmunoassay. Channel currents and membrane action potentials were recorded using the conventional whole-cell patch-clamp technique. Calcium imaging system was used to analyze intracellular Ca(2+) concentration ([Ca(2+)]i). The data show that under 16.7mmol/l glucose conditions uncarboxylated osteocalcin alone increased insulin secretion and [Ca(2+)]i, but with no such effects on insulin secretion and [Ca(2+)]i in the presence of a KV channel blocker, tetraethylammonium chloride. In the patch-clamp experiments, uncarboxylated osteocalcin lengthened action potential duration and significantly inhibited KV currents, but had no influence on the characteristics of voltage-gated calcium channels. These results indicate that KV channels are involved in uncarboxylated osteocalcin-regulated insulin secretion in rat pancreatic β cells. By inhibiting KV channels, uncarboxylated osteocalcin prolongs action potential duration, increases intracellular Ca(2+) concentration and finally promotes insulin secretion. This finding provides new insight into the mechanisms of osteocalcin-modulated insulin secretion.

Keywords: CaCl(2)·2H(2)O (PubChem CID: 6093260); CsCl (PubChem CID: 24293); EGTA (PubChem CID: 6207); Fluo 4AM (PubChem CID: 4060965); HEPES (PubChem CID: 23831); Insulin secretion; KCl (PubChem CID: 4873); KH(2)PO(4) (PubChem CID: 516951); NaCl (PubChem CID: 5234); Poly-d-lysine hydrobromide (PubChem CID: 16219815); Tetraethylammonium chloride (PubChem CID: 5946); Uncarboxylated osteocalcin; Voltage-gated potassium channel; β cell.