Ethanol reduces GABA_A α1 subunit receptor surface expression by a protein kinase Cγ-dependent mechanism in cultured cerebral cortical neurons

Prolonged ethanol exposure causes central nervous system hyperexcitability that involves a loss of GABAergic inhibition. We previously demonstrated that long-term ethanol exposure enhances the internalization of synaptic GABA _A receptors composed of α1β2/3γ2 subunits. However, the mechanisms of ethanol-mediated internalization are unknown. This study explored the effect of ethanol on surface expression of GABA_A α1 subunit-containing receptors in cultured cerebral cortical neurons and the role of protein kinase C (PKC) β, γ, and ε isoforms in their trafficking. Cultured neurons were prepared from rat pups on postnatal day 1 and maintained for 18 days. Cells were exposed to ethanol, and surface receptors were isolated by biotinylation and P2 fractionation, whereas functional analysis was conducted by whole-cell patch-clamp recording of GABA-and zolpidem-evoked responses. Ethanol exposure for 4 h decreased biotinylated surface expression of GABA_A receptor α1 subunits and reduced zolpidem (100 nM) enhancement of GABA-evoked currents. The PKC activator phorbol-12,13-dibutyrate mimicked the effect of ethanol, and the selective PKC inhibitor calphostin C prevented ethanol-induced internalization of these receptors. Ethanol exposure for 4 h also increased the colocalization and coimmunoprecipitation of PKCγ with α1 subunits, whereas PKCβ/α1 association and PKCε/α1 colocalization were not altered by ethanol exposure. Selective PKCγ inhibition by transfection of selective PKCγ small interfering RNAs blocked ethanol-induced internalization of GABA_A receptor α1 subunits, whereas PKCβ inhibition using pseudo-PKCβ had no effect. These findings suggest that ethanol exposure selectively alters PKCγ translocation to GABA_A receptors and PKCγ regulates GABA_A α1 receptor trafficking after ethanol exposure.