Mathews G C, Bolos-Sy A M, Covey D F, Rothman S M, Ferrendelli J A
Department of Molecular Biology, Washington University School of Medicine, St Louis, MO 63110, USA.
Neuropharmacology. 1996 Feb;35(2):123-36. doi: 10.1016/0028-3908(95)00180-8.
The GABAA receptor/chloride ionophore (GABAR) is allosterically modulated by several classes of anticonvulsant agents, including benzodiazepines and barbiturates, and some alkyl-substituted butyrolactones. To test the hypothesis that the anticonvulsant butyrolactones act at a distinct positive-modulatory site on the GABAR, we examined the physiological effects of a butyrolactone, a benzodiazepine and a barbiturate on GABA-mediated currents in voltage-clamped neurons and cells transfected with various subunit combinations. The butyrolactone, alpha-ethyl-alpha-methyl-gamma-thiobutyrolactone (alpha EMTBL), altered the EC50 for GABA and changed the apparent cooperativity of GABA responses. In contrast, the benzodiazepine chlordiazepoxide altered the EC50 for GABA with no effect on apparent cooperativity. The barbiturate phenobarbital altered both the EC50 and the amplitude of the maximal GABA response without altering apparent cooperativity. The GABA-mediated effect of the barbiturate, but not the benzodiazepine, added to the maximal effect of the butyrolactone, supporting the hypothesis that butyrolactones do not exert their effect at the barbiturate effector site. Both alpha EMTBL and phenobarbital potentiated GABA currents in transfected cells containing the alpha 1 beta 2 and alpha 1 gamma 2 subunit combinations, as well as alpha 1 subunits alone. Chlordiazepoxide had the minimum requirement of an alpha subunit and a gamma subunit. Specific GABARs lacking benzodiazepine or barbiturate modulation were tested for modulation by alpha EMTBL. The alpha 6 beta 2 gamma 2 combination was modulated by the butyrolactone but not chlordiazepoxide. However, GABARs comprising rho1 subunits were sensitive to both phenobarbital and alpha EMTBL. Although the molecular determinants for alpha EMTBL action appear similar to the barbiturates, our data support the conclusion that alpha EMTBL interacts with GABARs in a distinct manner from barbiturates and benzodiazepines.
γ-氨基丁酸A型受体/氯离子载体（GABAR）受到几类抗惊厥药物的变构调节，包括苯二氮䓬类和巴比妥类药物，以及一些烷基取代的丁内酯。为了验证抗惊厥丁内酯作用于GABAR上一个独特的正调节位点这一假说，我们研究了一种丁内酯、一种苯二氮䓬类药物和一种巴比妥类药物对电压钳制神经元和转染了各种亚基组合的细胞中γ-氨基丁酸（GABA）介导电流的生理效应。丁内酯α-乙基-α-甲基-γ-硫代丁内酯（αEMTBL）改变了GABA的半数有效浓度（EC50），并改变了GABA反应的表观协同性。相比之下，苯二氮䓬类药物氯氮卓改变了GABA的EC50，但对表观协同性没有影响。巴比妥类药物苯巴比妥改变了EC50和最大GABA反应的幅度，而没有改变表观协同性。巴比妥类药物（而非苯二氮䓬类药物）对GABA的介导作用增加了丁内酯的最大效应，支持了丁内酯不在巴比妥类效应位点发挥作用的假说。αEMTBL和苯巴比妥都增强了含有α1β2和α1γ2亚基组合以及单独α1亚基的转染细胞中的GABA电流。氯氮卓对α亚基和γ亚基有最低要求。测试了缺乏苯二氮䓬类或巴比妥类调节的特定GABARs对αEMTBL的调节作用。α6β2γ2组合受到丁内酯的调节，但不受氯氮卓的调节。然而，包含rho1亚基的GABARs对苯巴比妥和αEMTBL都敏感。尽管αEMTBL作用的分子决定因素似乎与巴比妥类药物相似，但我们的数据支持这样的结论，即αEMTBL与GABARs的相互作用方式与巴比妥类药物和苯二氮䓬类药物不同。
