Cachelin A B, Rust G
Department of Pharmacology, University of Berne, Switzerland.
Mol Pharmacol. 1994 Dec;46(6):1168-74.
We have investigated the functional properties of four rat neuronal nicotinic acetylcholine receptor types expressed in Xenopus oocytes after injection of pairwise combinations of mRNA encoding alpha 2 or alpha 3 receptor subunits with mRNA encoding beta 2 or beta 4 receptor subunits. Current responses evoked by rapid application of cholinergic agonists (acetylcholine, nicotine, or 1,1-dimethyl-4-phenylpiperazinium) were recorded from voltage-clamped oocytes. Substituting BaCl2 for CaCl2 in the external solution increased the apparent Kd values of beta 4 subunit-containing receptors for acetylcholine but decreased the apparent Kd values of beta 2 subunit-containing receptors. Inhibition curves for the cholinergic antagonist (+)-tubocurarine were measured in BaCl2 medium at low agonist concentrations. (+)-Tubocurarine was a competitive antagonist of acetylcholine at neuronal nicotinic acetylcholine receptors that coexpressed the beta 2 subunit; the estimated Kb values were 3.6 microM (alpha 2 beta 2 receptors) and 390 nM (alpha 3 beta 2 receptors). In contrast, (+)-tubocurarine enhanced the peak responses evoked by low acetylcholine concentrations at alpha 2 beta 4 and alpha 3 beta 4 neuronal nicotinic acetylcholine receptors, without being a partial agonist. The maximal increase was observed at 5 microM and 10 microM (+)-tubocurarine for alpha 2 beta 4 and alpha 3 beta 4 receptors, respectively. Higher (+)-tubocurarine concentrations inhibited cholinergic responses, thus yielding a "bell-shaped" concentration-response curve.
我们研究了在非洲爪蟾卵母细胞中表达的四种大鼠神经元烟碱型乙酰胆碱受体类型的功能特性，这些受体是通过注射编码α2或α3受体亚基的mRNA与编码β2或β4受体亚基的mRNA的两两组合而产生的。从电压钳制的卵母细胞中记录快速施加胆碱能激动剂（乙酰胆碱、尼古丁或1,1-二甲基-4-苯基哌嗪鎓）所诱发的电流反应。在外部溶液中用BaCl2替代CaCl2可增加含β4亚基的受体对乙酰胆碱的表观解离常数（Kd）值，但会降低含β2亚基的受体的表观Kd值。在低激动剂浓度下于BaCl2培养基中测量胆碱能拮抗剂（+）-筒箭毒碱的抑制曲线。（+）-筒箭毒碱是共表达β2亚基的神经元烟碱型乙酰胆碱受体上乙酰胆碱的竞争性拮抗剂；估计的平衡解离常数（Kb）值分别为3.6微摩尔（α2β2受体）和390纳摩尔（α3β2受体）。相比之下，（+）-筒箭毒碱增强了α2β4和α3β4神经元烟碱型乙酰胆碱受体在低乙酰胆碱浓度下诱发的峰值反应，但它不是部分激动剂。在α2β4和α3β4受体中，分别在5微摩尔和10微摩尔（+）-筒箭毒碱时观察到最大增加。更高浓度的（+）-筒箭毒碱会抑制胆碱能反应，从而产生一条“钟形”浓度-反应曲线。
