Somatostatin activates two types of inwardly rectifying K+ channels in MIN-6 cells.
Western blotting revealed the presence of five somatostatin receptor types, sst1, sst2, sst3, sst4 and sst5, in the mouse pancreatic -cell line MIN-6. In MIN-6 cells, glucose-induced electrical activity was potently (pEC50 = 12.7) and irreversibly reduced by somatostatin (SRIF-14); this was associated with hyperpolarization of the membrane potential (pEC50 = 11.2) and a decrease in the input resistance (pEC50 = 12.7). The effects of SRIF-14 were mimicked by 100 nM L-362,855 (a partial agonist at sst5 receptors), but not BIM-23027 or NNC-26,9100 (selective agonists at sst2 and sst4 receptors, respectively). CH-275 at 100 nM (a selective agonist at sst1 receptors) partially inhibited electrical activity but without membrane potential hyperpolarization. One hundred nanomolar SRIF-28 activated an inwardly rectifying K+ current (ISRIF) ISRIF was activated neither by 1 M BIM-23056 nor CYN-154806 (antagonists at sst5 and sst2 receptors, respectively). The activation of ISRIF by 100 nM SRIF-28 was, however, inhibited 93 % by BIM-23056; CYN-154806 had no effect. Both 100 nM glibenclamide and 200 M tolbutamide, blockers of the -cell ATP-sensitive K+ channel (K-ATP), reduced ISRIF by ~44 %, whereas 1 mM Ba2+ abolished ISRIF. In cell-attached patches, 100 nM SRIF-14 activated two types of single-channel currents whose properties were consistent with those of K-ATP and GIRK channels. In conclusion, somatostatin can inhibit glucose-induced electrical activity in MIN-6 cells by the combined activation of K-ATP and GIRK channels. Studies with selective agonists and antagonists are consistent with this effect being mediated by the sst5 receptor.
Smith
P A
PA
Glaxo Institute of Applied Pharmacology, Department of Pharmacology, Tennis Court Road, Cambridge CB2 1QJ, UK. pas59404@glaxowellcome.co.uk
Sellers
L A
LA
Humphrey
P P
PP
D000818:Animals; D002460:Cell Line; D005947:Glucose / Q000494:pharmacology; D015151:Immunoblotting; D007515:Islets of Langerhans / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D051379:Mice; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism*; D024661:Potassium Channels, Inwardly Rectifying; D020033:Protein Isoforms; D017481:Receptors, Somatostatin / Q000378:metabolism*; D013004:Somatostatin / Q000031:analogs & derivatives / Q000737:chemistry / Q000494:pharmacology*
D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D020033:Protein Isoforms; D017481:Receptors, Somatostatin; D013004:Somatostatin; D005947:Glucose