ADAPTATION OF GAMMA-AMINOBUTYRIC-ACID TYPE-A RECEPTORS TO ALCOHOL EXPOSURE - STUDIES WITH STABLY TRANSFECTED CELLS

We studied the adaptation of gamma-aminobutyric acid type A (GABA(A)) receptor function to chronic ethanol exposure in cells stably transfec ted with the following GABA(A) receptor subunits: alpha-1 beta-2 gamma -2L, alpha-1 beta-2 gamma-2S, alpha-1 beta-3 gamma-2S, alpha-1 beta-1, alpha-5 beta-3 gamma-3 and alpha-6 beta-3 gamma-2S. Chronic exposure to ethanol resulted in a decrease in muscimol-stimulated 36Cl(-) flux and a decrease in modulation of that flux by ethanol, flunitrazepam, 7 -4-dimethoxy-4-ethyl-beta-carboline-3-carboxylate and pregnanolone wit hout any change in the modulation by pentobarbital or zinc. Direct act ivation of the GABA(A) receptor by pentobarbital was enhanced by chron ic ethanol treatment. Reduction of the action of muscimol, ethanol and flunitrazepam differed in the duration and amount of ethanol required to see an effect. Reduction of the action of ethanol of alpha-1 beta- 2 gamma-2L cells occurred within 15 min and was near-maximal for 25 mM ethanol, whereas reduction of the actions of muscimol and flunitrazep am actions required hours of exposure and higher concentrations of eth anol. Chronic ethanol exposure produced a reduction in the E-max value for the action of muscimol for ail six subunit combinations, but quan tification of surface receptors by immunolabeling showed no change in GABA(A) receptor density. The differences in alcohol sensitivity and t ime courses for different effects of ethanol indicate multiple mechani sms of adaptation of GABA(A) receptors. Use of stably transfected cell s rules out ''subunit substitution'' as a mechanism for these changes and points to post-translational changes (e.g., phosphorylation, recep tor assembly) as the most likely mechanisms. These in vitro findings a re compared with results from in vivo studies.