Activation of protein kinase C inhibits kainate-induced currents in oocytes expressing glutamate receptor subunits.

The effect of protein kinase C (PKC) activation on maximal kainate (KA)-induced currents was studied in Xenopus oocytes expressing the glutamate receptor (GluR) subunits GluR3, GluR1 + 3, GluR2 + 3, and GluR6. The PKC activator phorbol 12-myristate 13-acetate (PMA) inhibited peak KA responses in a time-dependent manner. The magnitude of inhibition was greatest in GluR6-expressing oocytes. Desensitizing KA currents characterized by a peak, transient current followed by a slower, desensitizing current were observed in oocytes expressing GluR3 and GluR1 + 3 receptors. PMA inhibited the desensitization, and this effect could be observed before PMA's inhibition of peak current amplitude. PMA-mediated inhibition of both desensitization and peak current amplitude was prevented by intracellular injection of the protein kinase C (PKC) inhibitor peptide. These results suggest that the function of GluRs is regulated by PKC-dependent phosphorylation.