Taguchi J, Kuriyama K
Department of Pharmacology, Kyoto Prefectural University of Medicine, Japan.
J Pharmacol Exp Ther. 1990 May;253(2):558-66.
Effect of ethyl beta-carboline-3-carboxylate (beta-CCE) on the function of gamma-aminobutyric acid (GABA)A receptor/benzodiazepine receptor/chloride ion channel complex was studied. Beta-CCE noncompetitively and competitively inhibited [3H]flunitrazepam binding to benzodiazepine receptor, but not [3H]muscimol binding to GABAA receptor as well as t-[3H]butylbicycloorthobenzoate [( 3H] TBOB) binding to chloride ion channel, in particulate fraction of the mouse brain. Ro15-1788 also inhibited competitively [3H] flunitrazepam binding. On the other hand, the binding of beta-[3H]CCE was inhibited noncompetitively and competitively by clonazepam and competitively by Ro15-1788. In agreement with these results, benzodiazepines-stimulated [3H]muscimol binding was antagonized by beta-CCE and Ro15-1788. Gel column chromatography for the solubilized fraction from cerebral particulate fraction by 0.2% sodium deoxycholate (DOC-Na) in the presence of 1 M KCl indicated that beta-[3H]CCE binding site was eluted in the same fraction (molecular weight, 250,000) as the binding sites for [3H]flunitrazepam, [3H]muscimol and [3H]TBOB. GABA-stimulated 36Cl- influx into membrane vesicles prepared from the bovine cerebral cortex was stimulated and attenuated by flunitrazepam and beta-CCE, respectively. These effects of flunitrazepam and beta-CCE on the GABA-stimulated 36Cl- influx were antagonized by Ro15-1788. The present results suggest that the binding site for beta-CCE, which resides on GABAA receptor/benzodiazepine receptor/chloride ion channel complex, may be different from that for benzodiazepine. Possible roles of beta-CCE binding site in the allosteric inhibitions on benzodiazepine binding site as well as on the functional coupling between chloride ion channel and GABAA receptor are also suggested.
研究了β-咔啉-3-羧酸乙酯（β-CCE）对γ-氨基丁酸（GABA）A受体/苯二氮䓬受体/氯离子通道复合物功能的影响。在小鼠脑微粒体部分，β-CCE对[³H]氟硝西泮与苯二氮䓬受体的结合具有非竞争性和竞争性抑制作用，但对[³H]蝇蕈醇与GABAA受体的结合以及t-[³H]丁基双环邻苯二甲酸酯[（³H）TBOB]与氯离子通道的结合无抑制作用。Ro15-1788也竞争性抑制[³H]氟硝西泮的结合。另一方面，β-[³H]CCE的结合被氯硝西泮非竞争性和竞争性抑制，被Ro15-1788竞争性抑制。与这些结果一致，β-CCE和Ro15-1788拮抗苯二氮䓬类药物刺激的[³H]蝇蕈醇结合。在1 M KCl存在下，用0.2%脱氧胆酸钠（DOC-Na）对脑微粒体部分的溶解部分进行凝胶柱色谱分析表明，β-[³H]CCE结合位点与[³H]氟硝西泮、[³H]蝇蕈醇和[³H]TBOB的结合位点在同一部分（分子量250,000）被洗脱。氟硝西泮和β-CCE分别刺激和减弱了GABA刺激的³⁶Cl⁻流入从牛脑皮质制备的膜囊泡中。氟硝西泮和β-CCE对GABA刺激的³⁶Cl⁻流入的这些作用被Ro15-1788拮抗。目前的结果表明，位于GABAA受体/苯二氮䓬受体/氯离子通道复合物上的β-CCE结合位点可能与苯二氮䓬的结合位点不同。还提出了β-CCE结合位点在对苯二氮䓬结合位点的变构抑制以及氯离子通道与GABAA受体之间功能偶联中的可能作用。
