N-type Ca(2+) -channels in murine pancreatic beta-cells are inhibited by an exclusive coupling with somatostatin receptor subtype 1.
Somatostatin (SRIF) is a well-established inhibitor of insulin secretion, an effect in part mediated by a direct inhibition of voltage-operated Ca(2+)-channels. However, the identity of the somatostatin receptor subtypes (SSTRs) and voltage-operated Ca(2+)-channels involved in this process are unknown. Whole-cell perforated patch-clamp methods were applied to the murine pancreatic beta-cell line, MIN6, to explore the molecular pharmacology of this problem. SRIF-14 inhibited voltage-gated Ca(2+) currents (ICa(2+)) by 19 +/- 3% (n=24) with a pEC(50) = 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 ICa(2+) produced by SRIF and CH-275 was insensitive to pertussis toxin but was reversed by a prepulse to +100 mV. The inhibition of ICa(2+) by SRIF-14 was unaffected by 20 microm nifedipine, an inhibitor of L-type Ca(2+) channels. Application of the specific N-type Ca(2+) channel (Ca(v)2.2) inhibitor omega-conotoxin GV1A at 100 nm mimicked, and as a consequence abolished, the inhibitory effect of SRIF-14 on ICa(2+). SRIF selectively inhibits N-type Ca(2+)-channels in murine pancreatic beta-cells via exclusive coupling with SSTR1. These findings help explain how SSTR1 activation can inhibit insulin secretion in pancreatic beta-cells and suggest a possible new therapeutic lead for treatment of hyperinsulinemia.
School of Biomedical Sciences, Queens Medical Centre, Nottingham, UK. paul.a.smith@nottingham.ac.uk
Paul A
PA
Smith
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D020864:Calcium Channels, N-Type / Q000378:metabolism*; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology; D019204:GTP-Binding Proteins / Q000502:physiology; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000187:drug effects / Q000378:metabolism*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D051379:Mice; D011485:Protein Binding / Q000187:drug effects; D017481:Receptors, Somatostatin / Q000819:agonists / Q000378:metabolism*; D013004:Somatostatin / Q000031:analogs & derivatives / Q000494:pharmacology*; D020866:omega-Conotoxin GVIA / Q000494:pharmacology
C110576:CH 275; D002121:Calcium Channel Blockers; D020864:Calcium Channels, N-Type; D007328:Insulin; D017481:Receptors, Somatostatin; C101130:somatostatin receptor type 1; D013004:Somatostatin; D020866:omega-Conotoxin GVIA; D019204:GTP-Binding Proteins; D002118:Calcium