Glucagon-like peptide-1 inhibits pancreatic ATP-sensitive potassium channels via a protein kinase A- and ADP-dependent mechanism.
Glucagon-like peptide-1 (GLP-1) elicits a glucose-dependent insulin secretory effect via elevation of cAMP and activation of protein kinase A (PKA). GLP-1-mediated closure of ATP-sensitive potassium (K(ATP)) channels is involved in this process, although the mechanism of action of PKA on the K(ATP) channels is not fully understood. K(ATP) channel currents and membrane potentials were measured from insulin-secreting INS-1 cells and recombinant beta-cell K(ATP) channels. 20 nM GLP-1 depolarized INS-1 cells significantly by 6.68 +/- 1.29 mV. GLP-1 reduced recombinant K(ATP) channel currents by 54.1 +/- 6.9% in mammalian cells coexpressing SUR1, Kir6.2, and GLP-1 receptor clones. In the presence of 0.2 mM ATP, the catalytic subunit of PKA (cPKA, 20 nM) had no effect on SUR1/Kir6.2 activity in inside-out patches. However, the stimulatory effects of 0.2 mM ADP on SUR1/Kir6.2 currents were reduced by 26.7 +/- 2.9% (P < 0.05) in the presence of cPKA. cPKA increased SUR1/Kir6.2 currents by 201.2 +/- 20.8% (P < 0.05) with 0.5 mM ADP present. The point mutation S1448A in the ADP-sensing region of SUR1 removed the modulatory effects of cPKA. Our results indicate that PKA-mediated phosphorylation of S1448 in the SUR1 subunit leads to K(ATP) channel closure via an ADP-dependent mechanism. The marked alteration of the PKA-mediated effects at different ADP levels may provide a cellular mechanism for the glucose-sensitivity of GLP-1.
Light
Peter E
PE
Department of Pharmacology Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta, Canada T6G 2H7. peter.light@ualberta.ca
Manning Fox
Jocelyn E
JE
Riedel
Michael J
MJ
Wheeler
Michael B
MB
D018528:ATP-Binding Cassette Transporters; D000244:Adenosine Diphosphate / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D005934:Glucagon / Q000235:genetics / Q000378:metabolism; D052216:Glucagon-Like Peptide 1; D000067757:Glucagon-Like Peptide-1 Receptor; D006801:Humans; D007328:Insulin / Q000378:metabolism; D008969:Molecular Sequence Data; D010179:Pancreas / Q000201:enzymology / Q000378:metabolism*; D010446:Peptide Fragments / Q000235:genetics / Q000378:metabolism; D015221:Potassium Channels / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D024661:Potassium Channels, Inwardly Rectifying; D011498:Protein Precursors / Q000235:genetics / Q000378:metabolism; D011955:Receptors, Drug; D018027:Receptors, Glucagon / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D064233:Sulfonylurea Receptors
C577507:ABCC8 protein, human; D018528:ATP-Binding Cassette Transporters; C000593833:GLP1R protein, human; D000067757:Glucagon-Like Peptide-1 Receptor; D007328:Insulin; D010446:Peptide Fragments; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D011498:Protein Precursors; D011955:Receptors, Drug; D018027:Receptors, Glucagon; D064233:Sulfonylurea Receptors; D000244:Adenosine Diphosphate; D052216:Glucagon-Like Peptide 1; D000255:Adenosine Triphosphate; D005934:Glucagon; D017868:Cyclic AMP-Dependent Protein Kinases