Involvement of calmodulin in glucagon-like peptide 1(7-36) amide-induced inhibition of the ATP-sensitive K+ channel in mouse pancreatic beta-cells.
The present investigation was designed to examine whether calmodulin is involved in the inhibition of the ATP-sensitive K+ (K(ATP)) channel by glucagon-like peptide 1(7-36) amide (GLP-1) in mouse pancreatic beta-cells. Membrane potential, single channel and whole-cell currents through the K(ATP) channels, and intracellular free Ca2+ concentration ([Ca2+]i) were measured in single mouse pancreatic beta-cells. Whole-cell patch-clamp experiments with amphotericin-perforated patches revealed that membrane conductance at around the resting potential is predominantly supplied by the K(ATP) channels in mouse pancreatic beta-cells. The addition of 20 nM GLP-1 in the presence of 5 mM glucose significantly reduced the membrane K(ATP) conductance, accompanied by membrane depolarization and the generation of electrical activity. A calmodulin inhibitor N-(6-aminohexyl)-5-chloro-1-naphthalenesulphonamide (W-7, 20 microM) completely reversed the inhibitory actions of GLP-1 on the membrane K(ATP) conductance and resultant membrane depolarization. Cell-attached patch recordings confirmed the inhibition of the K(ATP) channel activity by 20 nM GLP-1 and its restoration by 20 microM W-7 or 10 microM calmidazolium at the single channel level. Bath application of 20 microM W-7 also consistently abolished the GLP-1-evoked increase in [Ca2+]i in the presence of 5 mM glucose. These results strongly suggest that the mechanisms by which GLP-1 inhibits the K(ATP) channel activity accompanied by the initiation of electrical activity in mouse pancreatic beta-cells include a calmodulin-dependent mechanism in addition to the well-documented activation of the cyclic AMP-protein kinase A system.
Ding
W G
WG
Department of Physiology, Shiga University of Medical Science, Shiga 520-2192, Japan. ding@belle.shiga-med.ac.jp
Kitasato
H
H
Matsuura
H
H
D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002147:Calmodulin / Q000037:antagonists & inhibitors / Q000378:metabolism*; D004594:Electrophysiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005934:Glucagon; D052216:Glucagon-Like Peptide 1; D004763:Glucagon-Like Peptides; D007004:Hypoglycemic Agents / Q000494:pharmacology; D007093:Imidazoles / Q000494:pharmacology; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D051379:Mice; D008813:Mice, Inbred ICR; D010446:Peptide Fragments / Q000494:pharmacology*; D015221:Potassium Channels / Q000378:metabolism*; D013449:Sulfonamides / Q000494:pharmacology; D014044:Tolbutamide / Q000494:pharmacology
D002147:Calmodulin; D004791:Enzyme Inhibitors; D007004:Hypoglycemic Agents; D007093:Imidazoles; D010446:Peptide Fragments; D015221:Potassium Channels; D013449:Sulfonamides; C061970:glucagon-like peptide 1 (7-36); C031938:calmidazolium; D004763:Glucagon-Like Peptides; C017967:W 7; D052216:Glucagon-Like Peptide 1; D000255:Adenosine Triphosphate; D005934:Glucagon; D014044:Tolbutamide; D002118:Calcium