Effects of insulin secretagogues on protein kinase C-catalyzed phosphorylation of an endogenous substrate in isolated pancreatic islets.
The influence of the insulin secretagogues, carbachol and glucose, on protein kinase C activation in isolated pancreatic islets has been examined by determination of the phosphorylation state of an endogenous 80-kDa protein substrate of protein kinase C. The islet 80-kDa protein was identified as the myristoylated alanine-rich C kinase substrate previously described (Stumpo D. J., Graff, J. M., Albert, K. A., Greengard, P., and Blackshear, P. J. (1989) Proc. Natl. Acad. Sci. U. S. A. 86, 4012-4016) by immunoprecipitation studies. The muscarinic agonist, carbachol (500 microM), induced insulin secretion and a time-dependent increase in the phosphorylation state of this protein in islets. This phosphorylation was maximal (220 +/- 24% of control) at 5 min and was suppressed by the protein kinase C inhibitor, staurosporine. Concentrations of glucose (28 mM) which induce maximal insulin secretion did not induce a statistically significant increase in 80-kDa phosphorylation. The combination of carbachol and a submaximally stimulatory concentration of glucose (10 mM), when added simultaneously, exerted a marked synergistic effect on insulin secretion and a synergistic effect on the phosphorylation of the 80-kDa protein kinase C substrate. These data suggest that the activation of protein kinase C may play an important role in carbachol-induced insulin secretion and in the potentiation by carbachol of insulin secretion induced by glucose. However, the activation of protein kinase C does not appear to be a primary determinant of insulin secretion induced by glucose alone.
Department of Pathology, Washington University School of Medicine, St. Louis, Missouri 63110.
R A
RA
Easom
M
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Landt
J R
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Colca
J H
JH
Hughes
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J
Turk
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M
McDaniel
D000470:Alkaloids / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002217:Carbachol / Q000494:pharmacology*; D005947:Glucose / Q000494:pharmacology*; D066298:In Vitro Techniques; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D008297:Male; D008970:Molecular Weight; D010743:Phospholipids / Q000494:pharmacology; D010750:Phosphoproteins / Q000096:biosynthesis* / Q000302:isolation & purification; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D019311:Staurosporine; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D000470:Alkaloids; D007328:Insulin; D010743:Phospholipids; D010750:Phosphoproteins; D002217:Carbachol; D011493:Protein Kinase C; D019311:Staurosporine; D005947:Glucose; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium