Association of protein kinase C with GABAA receptors containing α1 and α4 subunits in the cerebral cortex:: selective effects of chronic ethanol consumption

Previous studies have suggested that protein kinase C (PKC) isoforms differentially influence the sensitivity of gamma-aminobutyric acid(A) (GABA(A)) receptor responses in brain. Both PKCgamma and PKCepsilon knock-out mice exhibit altered ethanol potentiation of GABA(A) receptor mediated Cl- flux. Furthermore, chronic ethanol consumption alters GABA(A) receptor function and receptor subunit peptide expression by mechanisms that are not yet understood. The present study explored the possibility that PKC isoforms are directly associated with GABA(A) receptors, and this association is influenced by chronic ethanol exposure. GABA(A) receptors containing alpha1 or alpha4 subunits were immunoprecipitated from solubilized protein derived from the membrane fraction of rat cerebral cortex using selective antibodies. Immunoprecipitated receptors were screened by western blot analysis for the presence of PKCdelta, gamma and epsilon isoforms. We found pronounced labeling of PKCgamma but not PKCdelta or PKCepsilon in the alpha1 and alpha4 subunit immunoprecipitates. Immunoprecipitation with PKCgamma, but not with IgG antibody also yielded GABA(A) receptor alpha1 and alpha4 subunits in the immunoprecipitate. The association of PKCgamma with alpha1-containing receptors was decreased 44 +/- 11% after chronic ethanol consumption. In contrast, PKCgamma associated with alpha4-containing receptors was increased 32 +/- 7% after chronic ethanol consumption. These results suggest that PKCgamma may be involved in GABA(A) receptor adaptations following chronic ethanol consumption.