Hansen S L, Ebert B, Fjalland B, Kristiansen U
Department of Pharmacology, Royal Danish School of Pharmacy, 2 Universitetsparken, 2100 Copenhagen, Denmark.
Br J Pharmacol. 2001 Jun;133(4):539-49. doi: 10.1038/sj.bjp.0704121.
Based on an unexpected high maximum response to piperidine-4-sulphonic acid (P4S) at human alpha1alpha6beta2gamma2 GABA(A) receptors expressed in Xenopus oocytes attempts to correlate this finding with the pharmacological profile of P4S and other GABA(A) receptor ligands in neuronal cultures from rat cerebellar granule cells and rat cerebral cortex were carried out. GABA and isoguvacine acted as full and piperidine-4-sulphonic acid (P4S) as partial agonists, respectively, at alpha1beta2gamma2, alpha6beta2gamma2 and alpha1alpha6beta2gamma2 GABA receptors expressed in Xenopus oocytes with differences in potency. Whole-cell patch-clamp recordings were used to investigate the pharmacological profile of the partial GABA(A) receptor agonists 4,5,6,7-tetrahydroisoxazolo-(5,4-c)pyridin-3-ol (THIP), P4S, 5-(4-piperidyl)isoxazol-3-ol (4-PIOL), and 3-(4-piperidyl)isoxazol-5-ol (iso-4-PIOL), and the competitive GABA(A) receptor antagonists Bicuculline Methbromide (BMB) and 2-(3-carboxypropyl)-3-amino-6-methoxyphenyl-pyridazinium bromide (SR95531) on cerebral cortical and cerebellar granule neurons. In agreement with findings in oocytes, GABA, isoguvacine and P4S showed similar pharmacological profiles in cultured cortical and cerebellar neurones, which are known to express mainly alpha1, alpha2, alpha3, and alpha5 containing receptors and alpha1, alpha6 and alpha1alpha6 containing receptors, respectively. 4-PIOL and iso-4-PIOL, which at GABA(A) receptors expressed in oocytes were weak antagonists, showed cell type dependent potency as inhibitors of GABA mediated responses. Thus, 4-PIOL was slightly more potent at cortical neurones than at granule neurones and iso-4-PIOL was more potent in inhibiting isoguvacine-evoked currents at cortical than at granule neurons. Furthermore the maximum response to 4-PIOL corresponded to that of a partial agonist, whereas that of iso-4-PIOL gave a maximum response close to zero. It is concluded that the pharmacological profile of partial agonists is highly dependent on the receptor composition, and that small structural changes of a ligand can alter the selectivity towards different subunit compositions. Moreover, this study shows that pharmacological actions determined in oocytes are generally in agreement with data obtained from cultured neurons.
基于在非洲爪蟾卵母细胞中表达的人α1α6β2γ2 GABA(A)受体对哌啶-4-磺酸（P4S）出现意外的高最大反应，开展了将这一发现与P4S以及大鼠小脑颗粒细胞和大鼠大脑皮层神经元培养物中其他GABA(A)受体配体的药理学特征进行关联的尝试。在非洲爪蟾卵母细胞中表达的α1β2γ2、α6β2γ2和α1α6β2γ2 GABA受体上，GABA和异鹅膏蕈氨酸分别作为完全激动剂，哌啶-4-磺酸（P4S）作为部分激动剂，效力存在差异。采用全细胞膜片钳记录法研究部分GABA(A)受体激动剂4,5,6,7-四氢异恶唑并-(5,4-c)吡啶-3-醇（THIP）、P4S、5-(4-哌啶基)异恶唑-3-醇（4-PIOL）和3-(4-哌啶基)异恶唑-叔醇（异-4-PIOL）以及竞争性GABA(A)受体拮抗剂甲基溴化荷包牡丹碱（BMB）和2-(3-羧丙基)-3-氨基-6-甲氧基苯基哒嗪溴化物（SR95531）对大脑皮层和小脑颗粒神经元的药理学特征。与在卵母细胞中的发现一致，GABA、异鹅膏蕈氨酸和P4S在培养的皮层和小脑神经元中表现出相似的药理学特征，已知这些神经元分别主要表达含α1、α2、α3和α5的受体以及含α1、α6和α1α6的受体。4-PIOL和异-4-PIOL在卵母细胞中表达的GABA(A)受体上是弱拮抗剂，作为GABA介导反应的抑制剂，其效力表现出细胞类型依赖性。因此，4-PIOL在皮层神经元中的效力略高于颗粒神经元，而异-4-PIOL在皮层中抑制异鹅膏蕈氨酸诱发电流的效力高于颗粒神经元。此外，对4-PIOL的最大反应相当于部分激动剂的反应，而异-4-PIOL的最大反应接近于零。得出的结论是，部分激动剂的药理学特征高度依赖于受体组成，并且配体的微小结构变化可改变对不同亚基组成的选择性。此外，本研究表明在卵母细胞中确定的药理学作用通常与从培养神经元获得的数据一致。
