Department of Neuroscience, Physiology and Pharmacology, University College London, London, United Kingdom.
Mol Pharmacol. 2012 Nov;82(5):910-7. doi: 10.1124/mol.112.080259. Epub 2012 Aug 8.
Nicotinic acetylcholine receptors (nAChRs) are oligomeric transmembrane proteins in which five subunits coassemble to form a central ion channel pore. Conventional agonists, such as acetylcholine (ACh), bind to an orthosteric site, located at subunit interfaces in the extracellular domain. More recently, it has been demonstrated that nAChRs can also be activated by ligands binding to an allosteric transmembrane site. In the case of α7 nAChRs, ACh causes rapid activation and almost complete desensitization. In contrast, allosteric agonists such as 4-(4-bromophenyl)-3a,4,5,9b-tetrahydro-3H-cyclopenta[c] quin oline-8-sulfonamide (4BP-TQS) activate α7 nAChRs more slowly and cause only low levels of apparent desensitization. In the present study, single-channel patch-clamp recording has been used to investigate differences in the mechanism of activation of α7 nAChRs by ACh and 4BP-TQS. The most striking difference between activation by ACh and 4BP-TQS is in single-channel kinetics. In comparison with activation by ACh, single-channel open times and burst lengths are substantially longer (160-800-fold, respectively), and shut times are shorter (8-fold) when activated by 4BP-TQS. In addition, coapplication of ACh and 4BP-TQS results in a further increase in single-channel burst lengths. Mean burst lengths seen when the two agonists are coapplied (3099 ± 754 ms) are ~2.5-fold longer than with 4BP-TQS alone and ∼370-fold longer than with ACh alone. Intriguingly, the main single-channel conductance of α7 nAChRs, was significantly larger when activated by 4BP-TQS (100.3 ± 2.4 pS) than when activated by ACh (90.0 ± 2.7 pS), providing evidence that activation by allosteric and orthosteric agonists results in different α7 nAChRs open-channel conformations.
烟碱型乙酰胆碱受体 (nAChRs) 是一种寡聚跨膜蛋白，其中五个亚基共同组装形成中央离子通道孔。传统的激动剂，如乙酰胆碱 (ACh)，结合到位于细胞外结构域亚基界面的正位点。最近，已经证明 nAChRs 也可以被结合到变构跨膜位点的配体激活。在 α7 nAChRs 的情况下，ACh 引起快速激活和几乎完全脱敏。相比之下，变构激动剂，如 4-(4-溴苯基)-3a,4,5,9b-四氢-3H-环戊[c]喹啉-8-磺酰胺 (4BP-TQS)，激活 α7 nAChRs 的速度较慢，仅引起低水平的明显脱敏。在本研究中，使用单通道膜片钳记录技术研究了 ACh 和 4BP-TQS 激活 α7 nAChRs 的机制差异。ACh 和 4BP-TQS 激活之间最显著的区别在于单通道动力学。与 ACh 激活相比，当用 4BP-TQS 激活时，单通道开放时间和爆发长度显著延长（分别延长约 160-800 倍），而关闭时间缩短（约 8 倍）。此外，ACh 和 4BP-TQS 的共同应用导致单通道爆发长度进一步增加。当两种激动剂共同应用时观察到的平均爆发长度（3099 ± 754 ms）比单独用 4BP-TQS 长约 2.5 倍，比单独用 ACh 长约 370 倍。有趣的是，当用 4BP-TQS 激活时，α7 nAChRs 的主要单通道电导明显大于用 ACh 激活时（100.3 ± 2.4 pS 对 90.0 ± 2.7 pS），这表明变构和正位激动剂的激活导致不同的 α7 nAChRs 开放通道构象。
