Mortensen Martin, Wafford Keith A, Wingrove Peter, Ebert Bjarke
Department of Pharmacology, The Danish University of Pharmaceutical Sciences, 2 Universitetsparken, DK-2100 Copenhagen, Denmark.
Eur J Pharmacol. 2003 Aug 22;476(1-2):17-24. doi: 10.1016/s0014-2999(03)02125-3.
The present study examines the spontaneous channel activity of GABA(A) receptors and the pharmacology of various full agonists (gamma-aminobutyric acid (GABA), isoguvacine), partial agonists (4,5,6,7-tetrahydroisoxazolo-[5,4-c]pyridin-3-ol (THIP), piperidine-4-sulphonic acid (P4S), imidazole-4-acetic acid), competitive antagonists (bicuculline, 2-(3-carboxypropyl)-3-amino-6-(4 methoxyphenyl)pyridazinium bromide (SR95531)) and non-competitive antagonists (picrotoxinin, zinc). Experiments were performed on oocytes separately expressing human alpha1beta2gamma2S, alpha1beta3epsilon and alpha1beta2(L259S)gamma2S receptors using two-electrode voltage clamp electrophysiology. Quantifying spontaneous channel activity showed this varied significantly between the alpha1beta2gamma2S (0.2+/-0.07%), alpha1beta3epsilon (20+/-3%) and alpha1beta2(L259S)gamma2S (83+/-4%) receptors. A direct correlation was found between the relative agonist potencies and the level of spontaneous activity of the GABA(A) receptors. Furthermore, the maximum responses for partial agonists were increased as a function of increased levels of spontaneous activity. There was no relationship between the potency/efficacy of competitive antagonists and the degree of spontaneous activity. However, the non-competitive allosteric inhibitor picrotoxinin showed an opposite dependence on spontaneous activity compared to that seen for agonists, whereas zinc showed a more complex dependence on the receptor subunit composition. These novel findings indicate that the potency and efficacy of ligands acting on GABA(A) receptors are highly dependent on the level of spontaneous activity of the receptor.
本研究检测了GABA(A)受体的自发通道活性以及各种完全激动剂（γ-氨基丁酸（GABA）、异鹅去甲肾上腺素）、部分激动剂（4,5,6,7-四氢异恶唑并-[5,4-c]吡啶-3-醇（THIP）、哌啶-4-磺酸（P4S）、咪唑-4-乙酸）、竞争性拮抗剂（荷包牡丹碱、2-(3-羧丙基)-3-氨基-6-(4-甲氧基苯基)哒嗪溴化物（SR95531））和非竞争性拮抗剂（印防己毒素、锌）的药理学特性。使用双电极电压钳电生理学技术，分别对单独表达人α1β2γ2S、α1β3ε和α1β2(L259S)γ2S受体的卵母细胞进行实验。对自发通道活性进行定量分析显示，α1β2γ2S（0.2±0.07%）、α1β3ε（20±3%）和α1β2(L259S)γ2S（83±4%）受体之间的自发通道活性存在显著差异。发现GABA(A)受体的相对激动剂效力与自发活性水平之间存在直接相关性。此外，部分激动剂的最大反应随着自发活性水平的增加而增加。竞争性拮抗剂的效力/效能与自发活性程度之间没有关系。然而，与激动剂相比，非竞争性变构抑制剂印防己毒素对自发活性的依赖性相反，而锌对受体亚基组成的依赖性更为复杂。这些新发现表明，作用于GABA(A)受体的配体的效力和效能高度依赖于受体的自发活性水平。
