The effects of polymyxin B, a protein kinase C inhibitor, on insulin secretion from intact and permeabilized islets of Langerhans.

Polymyxin B (0.01-1 mM), a polyamine antibiotic, inhibited both phorbol ester- and glucose-stimulated insulin secretion from isolated rat islets of Langerhans. This inhibition was rapidly reversible. Assay of the cytosolic protein kinase C by measurement of incorporation of labelled phosphate into a histone substrate demonstrated the presence of activity in islet extracts which could be stimulated by 12-O-tetradecanoylphorbol-13-acetate and inhibited by polymyxin B. These results suggest that protein kinase C plays a role in glucose-induced insulin secretion.