Characterization of chloride efflux from GT1-7 neurons: lack of effect of ethanol on GABAA response.
The purpose of this study of GT1-7 neurons was to partially characterize basal Cl- transport and GABAA mediated Cl- efflux and to test the effect of ethanol on a GABAA receptor that lacks a gamma subunit. We measured GABAA function and Cl- transport with 36Cl-. Our results show that basal 36Cl- efflux varied with temperature at 4 degrees C, 23 degrees C, and 37 degrees C. At 23 degrees C, DIDS, an inhibitor of anion exchange, reduced basal 36Cl- efflux maximally by 79.6% with an IC50 of 42.1 microM, whereas bumetanide, an inhibitor of (Na-K-Cl) cotransport, had no effect on basal 36Cl- efflux at concentrations up to 150 microM. At 4 degrees C, muscimol, a GABAA receptor agonist, stimulated 36Cl- efflux with an EC50 of 1.47 microM. Bicuculline, a GABAA receptor antagonist, completely reversed the effect of 20 microM muscimol with an IC50 of 6.08 microM. Ethanol, at concentrations up to 87 mM (0.4% (w/v)), had no effect on muscimol-induced 36Cl- efflux at 4 degrees C or at 32 degrees C. Our results indicate that stimulation of GABAA receptors causes an efflux of Cl- from GT1-7 neurons. This finding is consistent with the concept that stimulation of GABAA receptors produces depolarization of the plasma membrane, increase in cytosolic [Ca2+], and GnRH release. Our results represent the first description of chloride transport in GT1-7 neurons and suggest the presence of a Cl- exchange, but not (Na-K-Cl), transporter mechanism. Furthermore, the lack of an effect of ethanol observed in this study is consistent with the idea that a gamma 2L subunit may be necessary for the effects of low concentrations of ethanol at GABAA receptors.
Javors
M A
MA
Department of Psychiatry, University of Texas Health Science Center, San Antonio 78284, USA. javors@uthscsa.edu
King
T S
TS
Chang
X
X
Ticku
M K
MK
Levinson
C
C
D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D000818:Animals; D001640:Bicuculline / Q000494:pharmacology; D002034:Bumetanide / Q000494:pharmacology; D002478:Cells, Cultured; D000697:Central Nervous System Stimulants / Q000494:pharmacology*; D002712:Chlorides / Q000378:metabolism*; D004232:Diuretics / Q000494:pharmacology; D000431:Ethanol / Q000494:pharmacology*; D018755:GABA Agonists / Q000494:pharmacology; D018756:GABA Antagonists / Q000494:pharmacology; D018757:GABA Modulators / Q000494:pharmacology; D051379:Mice; D009118:Muscimol / Q000494:pharmacology; D009474:Neurons / Q000737:chemistry / Q000166:cytology / Q000187:drug effects*; D010424:Pentobarbital / Q000494:pharmacology; D011963:Receptors, GABA-A / Q000737:chemistry / Q000378:metabolism*; D013696:Temperature
D000697:Central Nervous System Stimulants; D002712:Chlorides; D004232:Diuretics; D018755:GABA Agonists; D018756:GABA Antagonists; D018757:GABA Modulators; D011963:Receptors, GABA-A; D002034:Bumetanide; D009118:Muscimol; D000431:Ethanol; D010424:Pentobarbital; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D001640:Bicuculline