CHARACTERIZATION OF CHLORIDE EFFLUX FROM GT1-7 NEURONS - LACK OF EFFECT OF ETHANOL ON GABA(A) RESPONSE

The purpose of this study of GT1-7 neurons was to partially characteri ze basal Cl- transport and GABA(A) mediated Cl- efflux and to test the effect of ethanol on a GABA(A) receptor that lacks a gamma subunit. W e measured GABA(A) function and Cl- transport with Cl-36(-). Our resul ts show that basal Cl-36(-) efflux varied with temperature at 4 degree s C, 23 degrees C, and 37 degrees C. At 23 degrees C, DIDS, an inhibit or of anion exchange, reduced basal Cl-36(-) efflux maximally by 79.6% with an IC50 of 42.1 mu M, whereas bumetanide, an inhibitor of (Na-K- Cl) cotransport, had no effect on basal Cl-36(-) efflux at concentrati ons up to 150 mu M. At 4 degrees C, muscimol, a GABA(A) receptor agoni st, stimulated Cl-36(-) efflux with an EC50 of 1.47 mu M Bicuculline, a GABA(A) receptor antagonist, completely reversed the effect of 20 mu M muscimol with an IC50 of 6.08 mu M. Ethanol, at concentrations up t o 87 mM (0.4% (w/v)), had no effect on muscimol-induced Cl-36(-) efflu x at 4 degrees C or at 32 degrees C. Our results indicate that stimula tion of GABA(A) receptors causes an efflux of Cl- from GT1-7 neurons. This finding is consistent with the concept that stimulation of GABA(A ) receptors produces depolarization of the plasma membrane, increase i n cytosolic [Ca2+], and GnRH release. Our results represent the first description of chloride transport in GT1-7 neurons and suggest the pre sence of a Cl- exchange, but not (Na-K-Cl), transporter mechanism. Fur thermore, the lack of an effect of ethanol observed in this study is c onsistent with the idea that a gamma 2L subunit may be necessary for t he effects of low concentrations of ethanol at GABA(A) receptors. (C) 1998 Elsevier Science B.V.