Chronic ethanol treatment increases expression of inhibitory G-proteins and reduces adenylylcyclase activity in the central nervous system of two lines of ethanol-sensitive mice.

The possibility that a 7-day period of ethanol exposure could regulate expression of specific GTP-binding regulatory proteins was investigated in two distinct brain regions from two different lines of ethanol-sensitive mice. Following ethanol treatment, plasma membranes were prepared from cerebellum and pons of short and long sleep mice. Studies of membranes were performed to assess hormone-sensitive adenylylcyclase activity and to quantify expression of G-protein subunits. Immunoblot analysis showed that levels of Gi alpha(1) and Gi alpha(2) were markedly increased in cerebellar and pons membranes from ethanol-exposed mice compared to controls. Treatment of short sleep mice with ethanol enhanced ADP-ribosylation of both a 41- and a 39-40 kDa protein catalyzed by pertussis toxin. Ethanol did not alter expression of Gs alpha as assessed by immunoblot analysis, cholera toxin-dependent ADP-ribosylation, or by the ability of detergent extracted Gs alpha to reconstitute a functional adenylylcyclase in membranes from S49 cyc- murine lymphoma cells, a cell line which genetically lacks Gs alpha. Moreover, ethanol exposure did not influence levels of G(o) alpha or G beta 35-36 in either cerebellar or pons membranes. Cerebellar and pons membranes from ethanol-exposed short sleep mice demonstrated significantly less adenylylcyclase activity following stimulation with GTP, GTP gamma S, AlF, forskolin, and stimulatory ligands for three distinct receptors which couple to Gs alpha. Pretreatment of membranes with pertussis toxin reversed the ethanol-induced inhibition in adenylylcyclase activity. These observations were not limited to one line of mice but were also documented in a second line of ethanol-sensitive mice (e.g. long sleep). We conclude that ethanol exposure enhances expression of Gi alpha(1) and Gi alpha(2) in ethanol-sensitive mice, and is associated with decreased adenylylcyclase activity. Enhanced expression of Gi alpha(1) and Gi alpha(2) may contribute to impaired signal transduction in the central nervous system, and reduce the efficacy of neurotransmitters which signal through the adenylylcyclase system.

Duke Scholars

Author Anna Mae Diehl Medicine, Gastroenterology