Wafford K A, Bain C J, Whiting P J, Kemp J A
Neuroscience Research Centre, Merck, Sharp & Dohme Research Laboratories, Harlow, Essex, UK.
Mol Pharmacol. 1993 Aug;44(2):437-42.
The effect of benzodiazepines on the activity of gamma-aminobutyric acid (GABA)A receptors has been shown to be influenced by different alpha subunits and can also be affected by the presence of different gamma subunits. Previous studies have shown that receptors without a gamma subunit or those containing gamma 1 are modulated to a lesser degree by benzodiazepines. Using the Xenopus oocyte expression system to express different subunit combinations, a detailed analysis of the pharmacological modulation of GABAA receptors by various benzodiazepine site ligands has been carried out. We analyzed 14 compounds, varying through full agonist, partial agonist, antagonist, and inverse agonist, with receptors consisting of alpha 2 beta 1, alpha 2 beta 1 gamma 2S, and alpha 2 beta 1 gamma 1 and we demonstrate differences in their extent of potentiation by different benzodiazepine-type ligands. Most compounds showed negligible effects on alpha 2 beta 1 and most agonists, particularly the imidazopyridines zolpidem, alpidem, and AHR14,749, exhibited less potentiation with alpha 2 beta 1 gamma 1 than with alpha 2 beta 1 gamma 2S. The inverse agonists dimethoxy-4-ethyl-beta-carboline-3-carboxylate and Ro15-4513 did not act as inverse agonists and produced slight potentiation of alpha 2 beta 1 gamma 1 receptors. Concentration-response curves were constructed for five selected agonists to evaluate both affinity and efficacy differences between alpha 2 beta 1 gamma 2 and alpha 2 beta 1 gamma 1 receptors. Most compounds showed lower efficacy and up to 10-fold lower affinity with alpha 2 beta 1 gamma 1. Zolpidem showed slightly higher affinity but an extremely low efficacy; FG8205 also showed a markedly lower efficacy and was the most selective compound for alpha 2 beta 1 gamma 2S versus alpha 2 beta 1 gamma 1 receptors. CL218,872 showed high efficacy with alpha 2 beta 1 gamma 1 and affinity similar to that with alpha 2 beta 1 gamma 2 (being the least selective compound), suggesting that some low efficacy partial agonists with gamma 2-containing receptors may be more efficacious with gamma 1-containing receptors. The antagonists Ro15-1788 and CGS8216, although they blocked flunitrazepam potentiation of alpha 2 beta 1 gamma 2, could not block potentiation of alpha 2 beta 1 gamma 1. This study demonstrates that unique pharmacological profiles can be conferred by receptors containing different gamma subunits.
苯二氮䓬类药物对γ-氨基丁酸（GABA）A受体活性的影响已被证明受不同的α亚基影响，同时也会受到不同γ亚基存在的影响。先前的研究表明，不含γ亚基或含有γ1的受体受苯二氮䓬类药物的调节程度较低。利用非洲爪蟾卵母细胞表达系统来表达不同的亚基组合，已对各种苯二氮䓬类位点配体对GABAA受体的药理学调节进行了详细分析。我们分析了14种化合物，包括完全激动剂、部分激动剂、拮抗剂和反向激动剂，其作用的受体由α2β1、α2β1γ2S和α2β1γ1组成，并且我们证明了不同苯二氮䓬类配体对它们的增强程度存在差异。大多数化合物对α2β1的影响可忽略不计，并且大多数激动剂，尤其是咪唑吡啶类的唑吡坦、阿吡坦和AHR14,749，与α2β1γ2S相比，对α2β1γ1的增强作用较小。反向激动剂二甲氧基-4-乙基-β-咔啉-3-羧酸酯和Ro15-4513并未表现出反向激动剂的作用，而是对α2β1γ1受体产生了轻微的增强作用。构建了五种选定激动剂的浓度-反应曲线，以评估α2β1γ2和α2β1γ1受体之间的亲和力和效能差异。大多数化合物对α2β1γ1表现出较低的效能和高达10倍的低亲和力。唑吡坦表现出略高的亲和力但效能极低；FG8205也表现出明显较低的效能，并且是α2β1γ2S相对于α2β1γ1受体最具选择性的化合物。CL218,872对α2β1γ1表现出高效能，且亲和力与对α2β1γ2的亲和力相似（是最不具选择性的化合物），这表明一些含γ2受体的低效能部分激动剂对含γ1的受体可能更有效。拮抗剂Ro15-1788和CGS8216虽然能阻断氟硝西泮对α2β1γ2的增强作用，但无法阻断对α2β1γ1的增强作用。这项研究表明，含有不同γ亚基的受体可赋予独特的药理学特征。
