Jakubík J, Bacáková L, el-Fakahany E E, Tucek S
Institute of Physiology, Academy of Sciences of the Czech Republic, Prague.
J Pharmacol Exp Ther. 1995 Sep;274(3):1077-83.
The neuromuscular blocking drug alcuronium was found earlier to increase the affinity of muscarinic receptors for methyl-N-scopolamine (NMS). This effect could be observed in some but not in other tissues. Subtype selectivity of the positive allosteric action of alcuronium was now investigated in radioligand binding experiments in Chinese hamster ovary (CHO) cells stably transfected with the genes encoding the M1-M5 subtypes of muscarinic receptors. Alcuronium had a particularly high affinity for the M2 receptor subtype (Kd = 0.6 microM) and its affinity for muscarinic receptor subtypes diminished in the order M2 > M4 = M3 > M1 > M5. Alcuronium allosterically increased the binding of (3H)NMS to membranes containing receptors of the M2 (cooperativity factor alpha = 0.38) and M4 subtypes (alpha = 0.72) and inhibited the binding of (3H)NMS to membranes containing receptors of the M1, M3 and M5 subtypes (alpha = 3.35-4.35). The positive effects of alcuronium could also be observed in experiments with (3H)NMS binding to intact whole cells, indicating that the positive allosteric action of alcuronium occurs by alcuronium binding to receptor domains that are accessible from the extracellular space. Alcuronium diminished the affinity for (3H)quinuclidinyl benzilate [(3H)QNB] at all five subtypes of muscarinic receptors and slowed down the dissociation of both (3H)NMS and (3H)QNB; its decelerating effect on radioligand dissociation was most pronounced at the M2 receptor subtype. Differences between the effects of alcuronium on individual muscarinic receptor subtypes are apparently responsible for differences between the allosteric effects of alcuronium on muscarinic receptors in various tissues that had been described previously.
早期发现神经肌肉阻断药阿库氯铵可增加毒蕈碱受体对甲基-N-东莨菪碱（NMS）的亲和力。这种效应在某些组织中可以观察到，但在其他组织中则不然。现在，在稳定转染了编码毒蕈碱受体M1-M5亚型基因的中国仓鼠卵巢（CHO）细胞的放射性配体结合实验中，研究了阿库氯铵正变构作用的亚型选择性。阿库氯铵对M2受体亚型具有特别高的亲和力（Kd = 0.6 microM），其对毒蕈碱受体亚型的亲和力按M2>M4 = M3>M1>M5的顺序递减。阿库氯铵变构增加了（3H）NMS与含有M2（协同因子α = 0.38）和M4亚型受体的膜的结合，并抑制了（3H）NMS与含有M1、M3和M5亚型受体的膜的结合（α = 3.35-4.35）。在（3H）NMS与完整全细胞结合的实验中也可以观察到阿库氯铵的积极作用，这表明阿库氯铵的正变构作用是通过阿库氯铵与可从细胞外空间接近的受体结构域结合而发生的。阿库氯铵降低了对所有五种毒蕈碱受体亚型的（3H）喹核醇基苯甲酸酯[（3H）QNB]的亲和力，并减缓了（3H）NMS和（3H）QNB的解离；其对放射性配体解离的减速作用在M2受体亚型中最为明显。阿库氯铵对各个毒蕈碱受体亚型的作用差异显然是先前描述的阿库氯铵对各种组织中毒蕈碱受体变构作用差异的原因。
