cAMP-independent decrease of ATP-sensitive K+ channel activity by GLP-1 in rat pancreatic beta-cells.
Using the patch-clamp method, we studied the mechanism of depolarization of rat pancreatic beta-cells induced by glucagon-like peptide 1 (7-36) amide (GLP-1). GLP-1 caused depolarization in a concentration-dependent manner (0.2-100 nM). Exendin (9-39) amide, a GLP-1 receptor antagonist, prevented the GLP-1-induced depolarization. GLP-1 reduced tolbutamide-sensitive membrane currents evoked by voltage ramps from -90 to -50 mV, recorded in the perforated whole-cell configuration, suggesting that GLP-1 decreased the activity of the ATP-sensitive K+ channel (KATP). This GLP-1 effect was prevented by exendin (9-39) amide. In cells treated with Rp-cAMPS, an inhibitor of the cAMP-dependent protein kinase (PKA), GLP-1 still caused depolarization and reduced the whole-cell membrane current through KATP. Examined in the cell-attached configuration, 20 nM GLP-1, applied out of the patch, had little effect on KATP activity. In the inside-out configuration, the open time probability and the single-channel conductance of KATP in the absence of ATP inside the membrane were unaffected by the presence of 20 nM GLP-1 in the pipette. In both conditions, application of ATP to the inside of the membrane reduced KATP activity. The half-maximal concentrations (ki) of ATP were 11.6 microM without and 5.6 microM with 20 nM GLP-1 in the pipette (P<0.05). The values of the Hill coefficient (h) were 1.03 without and 1.01 with GLP-1. We conclude that GLP-1 reduces KATP activity by elevating the sensitivity of KATP to ATP, resulting in depolarization of pancreatic beta-cells. This GLP-1 action is independent of the cAMP signalling pathway.
Suga
S
S
Department of Physiology, Hirosaki University School of Medicine, Japan.
Kanno
T
T
Ogawa
Y
Y
Takeo
T
T
Kamimura
N
N
Wakui
M
M
D000200:Action Potentials / Q000187:drug effects; D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D000242:Cyclic AMP / Q000494:pharmacology*; D004553:Electric Conductivity; D005934:Glucagon / Q000494:pharmacology*; D052216:Glucagon-Like Peptide 1; D007515:Islets of Langerhans / Q000502:physiology*; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D010446:Peptide Fragments / Q000494:pharmacology*; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D011498:Protein Precursors / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar
D010446:Peptide Fragments; D015221:Potassium Channels; D011498:Protein Precursors; D052216:Glucagon-Like Peptide 1; D000255:Adenosine Triphosphate; D005934:Glucagon; D000242:Cyclic AMP