Ethanol Increases GABAA Responses in Cells Stably Transfected with Receptor Subunits

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Abstract
Ethanol enhancement of GABAA receptor function has been found in some, but not all, studies. These results suggest the existence of ethanol-sensitive and -resistant receptors that may differ in subunit composition, although methodological differences (e.g., 38Cl- flux versus membrane currents) could also contribute to the different results. To examine these possibilities, we used mouse L(tk-) cells stably transfected with α1+β or α+β1+γ2L GABAA receptor subunit DNAs and compared 38Cl flux with whole-cell, patch-clamp measurements of GABAA receptor function. Both techniques detected a similar modulation of the GABA receptor by ethanol, flunitrazepam, and pentobarbital. The potentiating action of ethanol required the -γ-subunit and was maximal at a concentration of 10 mm. Similar ethanol potentiation was obtained with brief (20 msec) or long (2 sec) applications of GABA. Analysis of data obtained from individual cells expressing α1β1-γ2L subunits showed considerable variability in sensitivity to ethanol, particularly with concentrations of 30 and 100 mm. Ethanol potentiated GABA action if the cells were grown on coverslips coated with polylysine, but had no effect on GABAA receptors of cells grown on uncoated coverslips. Thus, ethanol action was influenced by the growth matrix. Taken together, these data indicate that a y-subunit is necessary, but not sufficient, for ethanol sensitivity in this cell system. We suggest that posttranslational processing, particularly receptor phosphorylation, may also be important and that stably transfected cells will be useful in elucidating these events.