Puia G, Vicini S, Seeburg P H, Costa E
Fidia-Georgetown Institute for the Neurosciences, Georgetown University School of Medicine, Washington, DC 20007.
Mol Pharmacol. 1991 Jun;39(6):691-6.
gamma-Aminobutyric acid (GABA)-activated Cl- currents in neonatal rat cortical neurons and in cultured cells engineered for the expression of specific molecular forms of the GABAA receptor alpha, beta, and gamma subunits, were recorded with the patch-clamp technique in the whole-cell configuration. The effects of various allosteric modulators of GABAA receptors were determined. Diazepam and clonazepam showed greater efficacy as positive modulators of GABA-elicited currents in alpha 2 beta 1 gamma 2 or alpha 3 beta 1 gamma 2 receptors than in alpha 1 beta 1 gamma 2 or alpha 5 beta 1 gamma 2 receptors or in cortical neurons. Alpidem was more efficacious at alpha 1 beta 1 gamma 2 or alpha 2 beta 1 gamma 2 receptors than at alpha 1 beta 1 gamma 2 or alpha 5 beta 1 gamma 2 receptors or in cortical neurons. Conversely, zolpidem was equally efficacious for all these receptors except for alpha 5 beta 1 gamma 2. Both imidazopyridines (alpidem and zolpidem) were virtually ineffective at modulating the GABA response of alpha 5 beta 1 gamma 2 receptors and in almost all the receptors assembled from alpha 1, alpha 2, alpha 3 or alpha 5 subunits together with beta 1 and gamma 1 subunits. The beta-carboline derivatives methyl-6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate (DMCM) and methyl-beta-carboline-3-carboxylate (beta-CCM) elicited a positive allosteric modulation of alpha 1 beta 1 gamma 1 or alpha 2 beta 1 gamma 1 receptors, whereas they acted as negative allosteric modulators at nearly all other receptors tested, as they do in cortical neurons. Although the positive allosteric modulation by beta-carbolines never exceeded a doubling of the GABA response, DMCM was more efficacious at alpha 1 beta 1 gamma 1 receptors and beta-CCM was more efficacious at alpha 2 beta 1 gamma 1 receptors. DMCM was inactive at alpha 3 beta 1 gamma 1 receptors, whereas beta-CCM was virtually inactive at alpha 5 beta 1 gamma 1 receptors. The benzodiazepine 4'-chlorodiazepam, which is a negative modulator resistent to flumazenil inhibition, acted at all the various GABAA receptors that contained a gamma subunit.
采用全细胞膜片钳技术记录新生大鼠皮层神经元以及经基因工程改造用于表达特定分子形式的GABAA受体α、β和γ亚基的培养细胞中，γ-氨基丁酸（GABA）激活的Cl-电流。测定了GABAA受体各种变构调节剂的作用。地西泮和氯硝西泮作为GABA诱导电流的正性调节剂，在α2β1γ2或α3β1γ2受体中比在α1β1γ2或α5β1γ2受体或皮层神经元中表现出更高的效能。阿吡坦在α1β1γ2或α2β1γ2受体中的效能高于在α1β1γ2或α5β1γ2受体或皮层神经元中的效能。相反，唑吡坦对除α5β1γ2之外的所有这些受体的效能相同。两种咪唑吡啶类药物（阿吡坦和唑吡坦）在调节α5β1γ2受体以及几乎所有由α1、α2、α3或α5亚基与β1和γ1亚基组装而成的受体的GABA反应方面几乎无效。β-咔啉衍生物甲基-6,7-二甲氧基-4-乙基-β-咔啉-3-羧酸甲酯（DMCM）和甲基-β-咔啉-3-羧酸甲酯（β-CCM）对α1β1γ1或α2β1γ1受体产生正性变构调节作用，而在几乎所有其他测试受体中它们作为负性变构调节剂起作用，就像它们在皮层神经元中的作用一样。尽管β-咔啉的正性变构调节作用从未超过GABA反应的两倍，但DMCM在α1β1γ1受体中的效能更高，而β-CCM在α2β1γ1受体中的效能更高。DMCM对α3β1γ1受体无活性，而β-CCM对α5β1γ1受体几乎无活性。苯二氮䓬类药物4'-氯地西泮是一种对氟马西尼抑制有抗性的负性调节剂，作用于所有含有γ亚基的不同GABAA受体。
