Yang W, Drewe J A, Lan N C
CoCensys, Inc., Iruine, CA 92718, USA.
Eur J Pharmacol. 1995 Nov 30;291(3):319-25. doi: 10.1016/0922-4106(95)90072-1.
Benzodiazepines modulate gamma-aminobutyric acid (GABA)-evoked chloride currents through a specific binding site at the GABAA receptor-chloride channel complex. The heterogeneity of diazepam-sensitive benzodiazepine binding sites (type I and type II) has been identified by pharmacological approaches both with native receptors and recombinant receptors coexpressing alpha, beta and gamma subunits. In addition, two distinguishable diazepam-insensitive benzodiazepine sites are found, spatially distributed between cerebral cortical and cerebellar regions. Coexpression of alpha 6 with beta 2 and gamma 2L subunits creates a pharmacologically similar benzodiazepine receptor to the diazepam-insensitive site observed in cerebellum, however, there is no evidence regarding the possible subunit combination forming the DI site in cerebral tissues. Here we report the cloning of the human alpha 4 cDNA and its pharmacology by coexpression of this alpha 4 subunit with beta 2 and gamma 2L subunits. This recombinant receptor complex showed a high affinity for the previously described benzodiazepine partial agonist bretazenill, the pyrazoloquinoline compounds CGS-9895 and CGS-9896, as well as the inverse agonists DMCM (methyl 6,7-dimethoxy 4-ethyl-beta-carboline-3-carboxylate) and Ro15-4513 as determined by [3H]Ro15-4513 binding. However, it is insensitive to the benzodiazepine type I selective compounds CL218.872 (3-methyl-6-[3-(trifluoromethyl)[phenyl]-1,2,4-triazolo[4.3-b]pyridazine ) and zolpidem as well as the benzodiazepine full agonists diazepam, halazolam and midazolam. In addition, the benzodiazepine receptor ligands DMCM, beta-CCE (beta-carboline-3-carboxylate ethyl ester), Beta-CCM (beta-carboline-3-carboxylate methyl ester), FG-7142, CGS-9895 and CGS-9896 showed 7 to 10 times higher affinity for alpha 4 beta 2 gamma 2L. The pharmacology of the alpha 4 beta 2 gamma 2L receptor complex appears to resemble those of the diazepam-insensitive site found in the cerebral cortex. Our study thus suggests that this subpopulation of diazepam-insensitive GABAA receptors may be composed of alpha 4 beta 2 gamma 2L subunits.
苯二氮䓬类药物通过作用于GABAA受体 - 氯离子通道复合物上的特定结合位点来调节γ-氨基丁酸（GABA）诱发的氯离子电流。通过药理学方法，利用天然受体以及共表达α、β和γ亚基的重组受体，已鉴定出对安定敏感的苯二氮䓬结合位点的异质性（I型和II型）。此外，还发现了两个可区分的对安定不敏感的苯二氮䓬位点，在大脑皮质和小脑区域呈空间分布。α6与β2和γ2L亚基共表达产生一种药理学上与在小脑中观察到的对安定不敏感位点相似的苯二氮䓬受体，然而，尚无证据表明在脑组织中形成DI位点的可能亚基组合情况。在此，我们报告人α4 cDNA的克隆及其药理学特性，通过将该α4亚基与β2和γ2L亚基共表达来实现。这种重组受体复合物对先前描述的苯二氮䓬部分激动剂布雷替奈醇、吡唑并喹啉化合物CGS - 9895和CGS - 9896以及反向激动剂DMCM（6,7 - 二甲氧基 - 4 - 乙基 - β - 咔啉 - 3 - 羧酸甲酯）和Ro15 - 4513表现出高亲和力，这是通过[3H]Ro15 - 4513结合实验确定的。然而，它对苯二氮䓬I型选择性化合物CL218.872（3 - 甲基 - 6 - [3 - （三氟甲基）苯基] - 1,2,4 - 三唑并[4.3 - b]哒嗪）和唑吡坦以及苯二氮䓬完全激动剂地西泮、卤沙唑仑和咪达唑仑不敏感。此外，苯二氮䓬受体配体DMCM、β - CCE（β - 咔啉 - 3 - 羧酸乙酯）、β - CCM（β - 咔啉 - 3 - 羧酸甲酯）、FG - 7142、CGS - 9895和CGS - 9896对α4β2γ2L的亲和力高7至10倍。α4β2γ2L受体复合物药理学特性似乎与在大脑皮质中发现的对安定不敏感位点相似。因此，我们的研究表明，这种对安定不敏感的GABAA受体亚群可能由α4β2γ2L亚基组成。
