Atypical isoforms of pKc and insulin secretion from pancreatic beta-cells: evidence using Gö 6976 and Ro 31-8220 as Pkc inhibitors.

The involvement of protein kinase C (PKC) isoforms in glucose-induced insulin secretion was investigated by comparing the effects of the PKC inhibitors Gö 6976, which is PKC specific and selective for the Ca(2+)-dependent isoforms, and Ro 31-8220, a specific PKC inhibitor which does not discriminate between isoforms. Gö 6976 inhibited the Ca(2+)- and diacylglycerol (DAG)-dependent PKC activities in beta-cell extracts in vitro and fully inhibited insulin secretory responses of rat islets of Langerhans to the PKC activator 4 beta phorbol myristate acetate (PMA), suggesting that it was an effective inhibitor of the DAG-dependent isoforms of PKC in situ. However, glucose-induced insulin secretion from rat islets was not inhibited by Gö 6976, whereas secretory responses to glucose were partially inhibited by the non-isoform selective PKC inhibitor, Ro 31-8220. The simplest explanation of these results is that glucose-induced insulin secretion is dependent, at least in part, upon the activation of an atypical isoform(s) of PKC within the beta-cell.