Differential PKC Isoform Regulation of KATP Channel Trafficking and Function

Abstract

Pancreatic ATP sensitive potassium (KATP) channels play an important role in insulin secretion, linking the metabolic state and excitability of the beta cell. KATP channel function is under complex regulation by protein kinase C (PKC) with both activation and inhibition reported. To address this apparent contradiction we have employed a range of cell biological, electrophysiological and biochemical techniques to elucidate the mechanisms of PKC regulation of pancreatic KATP channels. Acute PKC activation (5 min) led to a large increase in KATP currents recorded from HEK cells stably expressing Kir6.2 and SUR1. This increase in currents was accompanied by increased colocalisation of KATP channels with classical PKC isoforms and was sensitive to inhibition by the classical PKC inhibitor Go6976. Prolonged (1 hour) activation of PKC however led to a significant reduction in KATP channel currents accompanied by a loss of channels from the cell surface and an increase in their lysosomal degradation. Decreased KATP channel surface expression was not sensitive to Go6976 indicating novel PKC isoforms. Both dominant negative PKC epsilon and PKC epsilon inhibiting peptides were able to inhibit the PKC mediated decrease in channel surface density. These data suggest that classical and novel PKC isoforms differentially regulate the function and trafficking of pancreatic KATP channels comprising Kir6.2 and SUR1. Further work is underway to assess the physiological significance of differential PKC isoform activation following pancreatic beta cell stimulation.This work is supported by the Medical Research Council, UK.