N-Type Ca2+-Channels in Murine Pancreatic β-Cells Are Inhibited by an Exclusive Coupling with Somatostatin Receptor Subtype 1

Abstract

Somatostatin (SRIF) is a well-established inhibitor of insulin secretion, an effect in part mediated by a direct inhibition of voltage-operated Ca2+-channels. However, the identity of the somatostatin receptor subtypes (SSTRs) and voltage-operated Ca2+-channels involved in this process are unknown. Whole-cell perforated patch-clamp methods were applied to the murine pancreatic β-cell line, MIN6, to explore the molecular pharmacology of this problem. SRIF-14 inhibited voltage-gated Ca2+ currents (ICa2+) by 19 ± 3% (n=24) with a pEC50 = 9.05 (95% confidence limits 9–9.1). This action was mimicked solely by 100 nm CH-275, a selective agonist at the somatostatin type 1 receptor (SSTR1), but not by 100 nm BIM-23027, L-362855, or NNC-269100; agonists selective for the other four SSTRs known to exist in MIN6. The inhibition of ICa2+ produced by SRIF and CH-275 was insensitive to pertussis toxin but was reversed by a prepulse to +100 mV. The inhibition of ICa2+ by SRIF-14 was unaffected by 20 μm nifedipine, an inhibitor of L-type Ca2+ channels. Application of the specific N-type Ca2+ channel (Cav2.2) inhibitor ω-conotoxin GV1A at 100 nm mimicked, and as a consequence abolished, the inhibitory effect of SRIF-14 on ICa2+. SRIF selectively inhibits N-type Ca2+-channels in murine pancreatic β-cells via exclusive coupling with SSTR1. These findings help explain how SSTR1 activation can inhibit insulin secretion in pancreatic β-cells and suggest a possible new therapeutic lead for treatment of hyperinsulinemia.In pancreatic β-cells, somatostatin selectively inhibits N-type, but not other, Ca2+-channels via a direct and exclusive coupling with somatostatin receptor subtype 1.