Zwart R, Vijverberg H P
Research Institute of Toxicology, Utrecht University, Utrecht, The Netherlands.
Mol Pharmacol. 1998 Dec;54(6):1124-31.
Nicotinic receptors generally are presumed to consist of two alpha and three non-alpha subunits. We varied the relative levels of expression of the neuronal nicotinic alpha4 and beta2 receptor subunits in Xenopus laevis oocytes by nuclear injection of cDNAs coding for these subunits in alpha:beta ratios of 9:1, 1:1, and 1:9. The sensitivities of the receptors to acetylcholine and d-tubocurarine were investigated in voltage-clamp experiments. For receptors expressed at the 9:1 and 1:1 alpha:beta ratios, the EC50 value of acetylcholine is approximately 60 microM. For the majority of the receptors expressed at the 1:9 alpha:beta ratio, the sensitivity to acetylcholine is enhanced 30-fold. No evidence for more than one type of acetylcholine binding site in a single receptor is obtained. The sensitivity to d-tubocurarine decreases with decreasing alpha:beta ratio. IC50 values of d-tubocurarine are 0.2, 0.5, and 2 microM for the 9:1, 1:1, and 1:9 alpha:beta ratios, respectively. At the 1:9 alpha:beta ratio, additional receptors with an IC50 value of 163 microM d-tubocurarine are expressed. At least two components with distinct sensitivities to d-tubocurarine are required to account for the shift in IC50. The combined agonist and antagonist effects reveal four distinct subtypes of alpha4beta2 nicotinic receptors. The results imply that the subunit stoichiometry of heteromeric alpha4beta2 acetylcholine receptors is not restricted to 2alpha:3beta.
通常认为烟碱型受体由两个α亚基和三个非α亚基组成。我们通过向非洲爪蟾卵母细胞核内注射编码这些亚基的cDNA，使神经元烟碱型α4和β2受体亚基的表达水平以9:1、1:1和1:9的α:β比例变化。在电压钳实验中研究了受体对乙酰胆碱和d -筒箭毒碱的敏感性。对于以9:1和1:1的α:β比例表达的受体，乙酰胆碱的EC50值约为60微摩尔。对于大多数以1:9的α:β比例表达的受体，对乙酰胆碱的敏感性增强了30倍。未获得单个受体中存在不止一种类型乙酰胆碱结合位点的证据。对d -筒箭毒碱的敏感性随α:β比例的降低而降低。对于9:1、1:1和1:9的α:β比例，d -筒箭毒碱的IC50值分别为0.2、0.5和2微摩尔。在1:9的α:β比例下，还表达了IC50值为163微摩尔d -筒箭毒碱的其他受体。需要至少两种对d -筒箭毒碱敏感性不同的成分来解释IC50的变化。激动剂和拮抗剂的联合作用揭示了α4β2烟碱型受体的四种不同亚型。结果表明，异源α4β2乙酰胆碱受体的亚基化学计量不限于2α:3β。
