The effects of protein kinase C (PKC) activators on gamma-aminoburyric acid (GABA) rho 1 receptor function were studied in rho 1 -expressing Xenopus oocytes. The PKC activator phorbol 12-myristate 13-acetate (PMA) but not the inactive analog phorbol 12-mono-myristate inhibited the GABA-gated chloride currents. Mezerein, a non-phorbol ester type PKC activator, also inhibited the rho 1 responses, but 8-chlorophenylthio-cyclic AMP, a protein kinase A activator, had no effect. The effect of PMA was significantly reduced by a PKC inhibitor, staurosporine. These results suggest that GABA rho 1 receptor function can be regulated by PKC-mediated phosphorylation events.