Chronic effects of ethanol on muscarinic acetylcholine receptors are modulated by protein kinase C

Abstract

We have previously demonstrated that long-term ethanol treatment increased the number and function of muscarinic acetylcholine receptors (mAChRs) in human neuroblastoma cells, but the molecular mechanisms involved in these changes are unknown. In the present study, the effect of protein kinase C (PKC) on these events was investigated in human neuroblastoma SH-SY5Y cells. Following exposure to 100 mM ethanol for 2 days, both [³H]N-methylscopolamine binding and carbachol-stimulated I(1,4,5)P₃formation were increased. When cells were cultured in the presence of 12-O-tetradecanoylphorbol 13-acetate (TPA), a potent activator of PKC, the effects of ethanol on mAChR number were totally inhibited but ethanol still potentiated carbacholstimulated I(1,4,5)P₃ formation in TPA treated cells. TPA dose-dependently inhibited carbochol-stimulated I(1,4,5)P₃ formation and this effect appeared to be independent of PKC phosphorylating activity. On the other hand, PKC inhibitors mimicked ethanol effects on mAChR number and function. Selective inhibition of classical PKC isozymes with 1 μΜ Gö 6976 for 2 days caused an increase in mAChR number and function, suggesting a role for these isozymes in ethanol-induced upregulation of mAChRs. These data indicate that longterm ethanol treatment may upregulate the number of mAChRs by counteracting PKC-mediated phosphorylation. The effects of ethanol on receptor-coupled phosphoinositide hydrolysis appear to be independent of PKC activity.