Brunner F, Waelbroeck M, Christophe J
Eur J Pharmacol. 1986 Aug 7;127(1-2):17-25. doi: 10.1016/0014-2999(86)90201-3.
In an attempt to determine if the selectivity of secoverine observed in vivo and in isolated tissues might be due to selective association with muscarinic receptor subtypes, we analyzed the binding of secoverine to three different receptors with specific radioligands: rat cardiac receptors (M2 receptors with low affinity for atropine), and rat cerebral cortical M1 receptors and M2 receptors with high affinity for atropine. At concentrations up to 10(-6) M, secoverine interaction with muscarinic receptors was competitive and of high affinity (Ki 4.10(-9) M) for cardiac and brain receptors. A detailed analysis using, in addition to [3H]N-methylscopolamine, the agonist [3H]oxotremorine-M (selective for high affinity binding sites at cardiac receptors) and the M1-selective antagonist [3H]pirenzepine at brain receptors, revealed identical affinities towards both receptor types, making it unlikely that secoverine distinguished the different muscarinic receptor subtypes. At concentrations between 10(-6) and 10(-3) M, secoverine interaction with an additional receptor site resulted in profound changes of tracer kinetics, suggesting the formation of a ternary complex (secoverine-radioligand-muscarinic receptor). The potency of secoverine for provoking this allosteric interaction was both tracer- and tissue-dependent. It is concluded that secoverine does not differentiate between M1, brain M2 and cardiac M2 receptors or between cardiac receptors with high, low and very low affinity for agonists. At very high concentrations secoverine recognized an allosteric site on the muscarinic receptors and reduced the dissociation rates of the 3H-ligands.
为了确定在体内和离体组织中观察到的西维美林的选择性是否可能归因于与毒蕈碱受体亚型的选择性结合，我们用特异性放射性配体分析了西维美林与三种不同受体的结合：大鼠心脏受体（对阿托品亲和力低的M2受体），以及对阿托品亲和力高的大鼠大脑皮质M1受体和M2受体。在浓度高达10⁻⁶ M时，西维美林与毒蕈碱受体的相互作用具有竞争性，对心脏和脑受体具有高亲和力（Ki 4×10⁻⁹ M）。除了[³H]N-甲基东莨菪碱外，还使用激动剂[³H]氧代震颤素-M（对心脏受体的高亲和力结合位点具有选择性）和脑受体处的M1选择性拮抗剂[³H]哌仑西平进行详细分析，结果显示对两种受体类型的亲和力相同，这使得西维美林不太可能区分不同的毒蕈碱受体亚型。在10⁻⁶至10⁻³ M之间的浓度下，西维美林与另一个受体位点的相互作用导致示踪剂动力学发生深刻变化，表明形成了三元复合物（西维美林-放射性配体-毒蕈碱受体）。西维美林引发这种变构相互作用的效力既取决于示踪剂，也取决于组织。得出的结论是，西维美林不能区分M1、脑M2和心脏M2受体，也不能区分对激动剂具有高、低和极低亲和力的心脏受体。在非常高的浓度下，西维美林识别毒蕈碱受体上的一个变构位点，并降低了³H-配体的解离速率。
