Effect of glucagon and cyclic adenosine 3',5'-monophosphate on protein phosphorylation in rat pancreatic islets.
Isolated rat pancreatic islets, incubated in the presence of extracellular 32Pi to a state of steady 32P incorporation into cellular phosphopeptides, were exposed to glucagon, (Bu)2cAMP, or somatostatin for 10 min. In other experiments, homogenates of rat islets were phosphorylated using [gamma-32P]ATP with or without cAMP. Proteins were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and phosphorylation of proteins was measured by liquid scintillation counting of gel slices. Glucagon (2.9 X 10(-7) M) stimulated the phosphorylation of 15 polypeptides (by approximately 20-50%) with major phosphorylation of proteins with mol wts of 138,000, 93,000, 53,000, 49,000, 35,000, 27,000 and 15,000 in intact rat islets and also stimulated insulin release by 202%. Somatostatin (6.6 X 10(-7) M) inhibited all the glucagon-stimulated phosphorylation by approximately 15-30% and also inhibited the glucagon-stimulated insulin release by 46%. (Bu)2cAMP (10(-3) M) stimulated 32P incorporation (by approximately 20-50%) into the same 15 peptides as did glucagon and also stimulated insulin release by 169%. When homogenates of rat islets were used. cAMP (10(-6) M) stimulated the phosphorylation of proteins (by approximately 25-60%) to an extent similar to that seen in the presence of glucagon or (Bu)2cAMP in intact islets. These findings indicate that the glucagon-stimulated phosphorylation of rat islet proteins may be mediated by cAMP-dependent protein kinase and that protein phosphorylation may be important in mediating the glucagon-stimulated insulin release.
D000818:Animals; D003994:Bucladesine / Q000494:pharmacology; D000242:Cyclic AMP / Q000494:pharmacology*; D005934:Glucagon / Q000494:pharmacology*; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D008970:Molecular Weight; D010766:Phosphorylation; D011506:Proteins / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013004:Somatostatin / Q000494:pharmacology
D011506:Proteins; D013004:Somatostatin; D003994:Bucladesine; D005934:Glucagon; D000242:Cyclic AMP