Protein kinase C (PKC) has been generally accepted to play a key role in stimulus-response coupling in various secretory cells, including pancreatic islets and pancreatic acini. The enzyme exists as a large family of multiple subspecies with highly related structures (α-, βI-, β:II-, γ-, δ-, ε-, and ζ-PKC). With an immunocytochemical procedure with subspecies-specific antibodies, βII-PKC-like immunoreactivity was identified to localize in the β-cells of the rat pancreatic islets. Neither βI- nor γ-PKC-like immunoreactivity was found in both islets and acini. Biochemical analysis confirmed that the rat whole pancreatic tissues contain a significant amount of α-PKC and a minute amount of βII-PKC but neither βI- nor γ-PKC. On the other hand, βII-PKC—like immunoreactivity was not detected in rat insulinoma cells, in which insulin secretion was induced in response to 12-O-tetradecanoylphorbol-13-acetate and carbachol but not in response to glucose. These findings suggest that βII-PKC is the major, if not the sole, subspecies of PKC in β-cells of rat pancreatic islets and a possible candidate for involvement in glucose-induced insulin secretion.

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