Department of Neurology, Yunfu People's Hospital, Yunfu, 527300, China.
Department of Neurobiology, Barrow Neurological Institute, St Joseph's Hospital and Medical Center, Phoenix, AZ, 85013, USA.
Acta Pharmacol Sin. 2018 Oct;39(10):1571-1581. doi: 10.1038/aps.2017.209. Epub 2018 May 24.
Neuronal nicotinic acetylcholine receptors containing α6 subunits (α6-nAChRs) show highly restricted distribution in midbrain neurons associated with pleasure, reward, and mood control, suggesting an important impact of α6-nAChRs in modulating mesolimbic functions. However, the function and pharmacology of α6-nAChRs remain poorly understood because of the lack of selective agonists for α6-nAChRs and the challenging heterologous expression of functional α6-nAChRs in mammalian cell lines. In particular, the α6 subunit is commonly co-expressed with α4-nAChRs in the midbrain, which masks α6-nAChR (without α4) function and pharmacology. In this study, we systematically profiled the pharmacology and function of α6-nAChRs and compared these properties with those of α4β2 nAChRs expressed in the same cell line. Heterologously expressed human α6/α3 chimeric subunits (α6 N-terminal domain joined with α3 trans-membrane domains and intracellular loops) with β2 and β3 subunits in the human SH-EP1 cell line (α6-nAChRs) were used. Patch-clamp whole-cell recordings were performed to measure these receptor-mediated currents. Functionally, the heterologously expressed α6-nAChRs exhibited excellent function and showed distinct nicotine-induced current responses, such as kinetics, inward rectification and recovery from desensitization, compared with α4β2-nAChRs. Pharmacologically, α6-nAChR was highly sensitive to the α6 subunit-selective antagonist α-conotoxin MII but had lower sensitivity to mecamylamine and dihydro-β-erythroidine. Nicotine and acetylcholine were found to be full agonists for α6-nAChRs, whereas epibatidine and cytisine were determined to be partial agonists. Heterologously expressed α6-nAChRs exhibited pharmacology and function distinct from those of α4β2-nAChRs, suggesting that α6-nAChRs may mediate different cholinergic signals. Our α6-nAChR expression system can be used as an excellent cell model for future investigations of α6-nAChR function and pharmacology.
含有α6 亚基的神经元烟碱型乙酰胆碱受体（α6-nAChRs）在与愉悦、奖励和情绪控制相关的中脑神经元中呈现出高度受限的分布，表明α6-nAChRs 在调节中边缘系统功能方面具有重要影响。然而，由于缺乏α6-nAChRs 的选择性激动剂以及在哺乳动物细胞系中功能性α6-nAChRs 的异源表达具有挑战性，因此α6-nAChRs 的功能和药理学仍知之甚少。特别是，α6 亚基通常与中脑的α4-nAChRs 共同表达，这掩盖了α6-nAChR（无α4）的功能和药理学。在这项研究中，我们系统地分析了α6-nAChRs 的药理学和功能，并将这些特性与在同一细胞系中表达的α4β2 nAChRs 进行了比较。在人 SH-EP1 细胞系（α6-nAChRs）中使用带有β2 和β3 亚基的人α6/α3 嵌合亚基（α6 N 端结构域与α3 跨膜结构域和细胞内环连接）进行异源表达。进行膜片钳全细胞记录以测量这些受体介导的电流。功能上，与α4β2-nAChRs 相比，异源表达的α6-nAChRs 表现出出色的功能，并表现出明显的尼古丁诱导的电流反应，例如动力学、内向整流和脱敏后恢复。药理学上，α6-nAChR 对α6 亚基选择性拮抗剂α-芋螺毒素 MII 高度敏感，但对美加明和二氢-β-erythroidine 的敏感性较低。发现尼古丁和乙酰胆碱是α6-nAChRs 的完全激动剂，而 epibatidine 和 cytisine 是部分激动剂。异源表达的α6-nAChRs 表现出与α4β2-nAChRs 不同的药理学和功能，表明α6-nAChRs 可能介导不同的胆碱能信号。我们的α6-nAChR 表达系统可用作未来研究α6-nAChR 功能和药理学的优秀细胞模型。
