Javors M A, King T S, Chang X, Ticku M K, Levinson C
Department of Psychiatry, University of Texas Health Science Center, San Antonio 78284, USA.
Brain Res. 1998 Jan 12;780(2):183-9. doi: 10.1016/s0006-8993(97)01134-7.
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.
本研究对GT1-7神经元的目的是部分表征基础氯离子转运以及GABAA介导的氯离子外流，并测试乙醇对缺乏γ亚基的GABAA受体的影响。我们用36Cl-测量了GABAA功能和氯离子转运。我们的结果表明，基础36Cl-外流在4℃、23℃和37℃时随温度变化。在23℃时，阴离子交换抑制剂DIDS最大程度地降低基础36Cl-外流79.6%，IC50为42.1μM，而（钠-钾-氯）协同转运抑制剂布美他尼在浓度高达150μM时对基础36Cl-外流没有影响。在4℃时，GABAA受体激动剂蝇蕈醇刺激36Cl-外流，EC50为1.47μM。GABAA受体拮抗剂荷包牡丹碱以6.08μM的IC50完全逆转20μM蝇蕈醇的作用。乙醇浓度高达87mM（0.4%（w/v））时，在4℃或32℃对蝇蕈醇诱导的36Cl-外流没有影响。我们的结果表明，GABAA受体的刺激导致氯离子从GT1-7神经元外流。这一发现与GABAA受体刺激导致质膜去极化、胞质[Ca2+]增加和促性腺激素释放激素释放的概念一致。我们的结果首次描述了GT1-7神经元中的氯离子转运，并提示存在氯离子交换而非（钠-钾-氯）转运机制。此外，本研究中观察到的乙醇无作用与低浓度乙醇在GABAA受体发挥作用可能需要γ2L亚基的观点一致。
