Chronic ethanol consumption enhances internalization of alpha1 subunit-containing GABAA receptors in cerebral cortex

The molecular mechanisms that underlie ethanol dependence involve alterations in the functional properties and subunit expression of GABAA receptors. Chronic ethanol exposure decreases GABAA receptor alpha1 subunits and increases alpha4 subunit levels in cerebral cortical membranes. This study explored the effect of chronic ethanol exposure on internalization of GABAA/benzodiazepine receptors. Chronic ethanol exposure increased alpha1 subunit levels by 46 +/- 12% and [3H]flunitrazepam binding by 35 +/- 9% in the clathrin-coated vesicle (CCV) fraction. There was a corresponding 34 +/- 8% decrease in alpha1 peptide expression and 37 +/- 6% decrease in [3H]flunitrazepam binding in the synaptic fraction. Chronic ethanol consumption also increased the alpha1 subunit immunoprecipitate in the cytosolic fraction (77 +/- 22%), measured by western blot analysis. Moreover, co-immunoprecipitation of both clathrin and adaptin-alpha with alpha1 subunits was increased in the cytosolic fraction, suggesting that alpha1 subunit endocytosis is enhanced by chronic ethanol consumption. In contrast, alpha4 subunit peptide levels were not altered in the CCV fraction despite a 39 +/- 13% increase in peptide levels in the synaptic fraction of cortex. Moreover, acute ethanol exposure did not alter alpha1 subunit peptide expression or [3H]flunitrazepam binding in the synaptic or CCV fractions. These results suggest that chronic ethanol consumption selectively increases internalization of alpha1 subunit-containing GABAA receptors in cerebral cortex.