Christopoulos A, Pierce T L, Sorman J L, El-Fakahany E E
Division of Neuroscience Research in Psychiatry, University of Minnesota Medical School, Minneapolis, Minnesota 55455, USA.
Mol Pharmacol. 1998 Jun;53(6):1120-30.
We investigated the molecular nature of the interaction between the functionally selective M1 muscarinic acetylcholine receptor (mAChR) agonist xanomeline and the human M1 mAChR expressed in Chinese hamster ovary (CHO) cells. In contrast to the non-subtype-selective agonist carbachol, xanomeline demonstrated M1 mAChR binding that was resistant to extensive washout, resulting in a significant reduction in apparent N-[3H]methylscopolamine saturation binding affinity in intact cells. Functional assays, using both M1 mAChR-mediated phosphoinositide hydrolysis and activation of neuronal nitric oxide synthase, confirmed that this persistent binding resulted in elevated basal levels of system activity. Furthermore, this phenomenon could be reversed by the addition of the antagonist atropine. However, pharmacological analysis of the inhibition by atropine of xanomeline-mediated functional responses indicated a possible element of noncompetitive behavior that was not evident in several kinetic and equilibrium binding experimental paradigms. Taken together, our findings indicate for the first time a novel mode of interaction between an mAChR agonist and the M1 mAChR, which may involve unusually avid binding of xanomeline to the receptor. This yields a fraction of added agonist that is retained at the level of the receptor compartment to persistently bind to and activate the receptor subsequent to washout. The results of the current study suggest that elucidation of the mechanism or mechanisms of interaction of xanomeline with the M1 mAChR is particularly important in relation to the potential therapeutic use of this agent in the treatment of Alzheimer's disease.
我们研究了功能选择性M1毒蕈碱型乙酰胆碱受体（mAChR）激动剂占诺美林与中国仓鼠卵巢（CHO）细胞中表达的人M1 mAChR之间相互作用的分子本质。与非亚型选择性激动剂卡巴胆碱不同，占诺美林表现出对广泛洗脱具有抗性的M1 mAChR结合，导致完整细胞中表观N-[3H]甲基东莨菪碱饱和结合亲和力显著降低。使用M1 mAChR介导的磷酸肌醇水解和神经元型一氧化氮合酶激活的功能测定证实，这种持续结合导致系统活性的基础水平升高。此外，加入拮抗剂阿托品可逆转此现象。然而，阿托品对占诺美林介导的功能反应抑制的药理学分析表明存在非竞争性行为的可能因素，这在几种动力学和平衡结合实验范式中并不明显。综上所述，我们的研究结果首次表明mAChR激动剂与M1 mAChR之间存在一种新的相互作用模式，这可能涉及占诺美林与受体异常紧密的结合。这会产生一部分添加的激动剂，在洗脱后仍保留在受体区室水平，持续结合并激活受体。当前研究结果表明，阐明占诺美林与M1 mAChR相互作用的机制对于该药物在治疗阿尔茨海默病中的潜在治疗用途尤为重要。
