Moscona-Amir E, Egozi Y, Henis Y I, Sokolovsky M
Neuroendocrinology. 1985 Jun;40(6):483-92. doi: 10.1159/000124119.
The effect of Ca2+ on the biochemical characteristics of muscarinic receptors in the adenohypophysis of male and female rats at the various stages of the estrous cycle was investigated in binding experiments using the specific muscarinic antagonist N-methyl-4-piperidyl benzylate ( [3H]-4NMPB) and the muscarinic agonist oxotremorine. By using Ca2+ chelators such as EGTA, and Ca2+ channel blockers such as D-600, we showed that Ca2+ profoundly alters the binding characteristics of both antagonists and agonists to the muscarinic receptors. In female rats the effect of Ca2+ on antagonist binding is mainly on the maximal binding capacity of the receptors, while changes in the dissociation constants are much more moderate. The effect is expressed in the ability of Ca2+ to expose or to eliminate binding sites as a function of the estrous cycle. In agonist binding, the presence of Ca2+ has a pronounced effect on the proportion of high-affinity binding sites, which parallels the changes induced in antagonist binding throughout the estrous cycle. Interestingly, the natural progression of the cycle from diestrus 2 to the estrous stage undergoes a change identical to that occurring in vitro upon Ca2+ removal. D-600 can completely block the effect of Ca2+ on the binding of both [3H]-4NMPB and oxotremorine. The concentration of D-600 required in order to induce such blocking is also dependent on the estrous cycle. It appears that the progression of the estrous cycle is accompanied by changes in the muscarinic receptors which may in turn be coupled to Ca2+ channels.
利用特异性毒蕈碱拮抗剂N-甲基-4-哌啶基苯甲酸苄酯（[3H]-4NMPB）和毒蕈碱激动剂氧化震颤素，通过结合实验研究了钙离子对处于发情周期不同阶段的雄性和雌性大鼠腺垂体中毒蕈碱受体生化特性的影响。通过使用乙二醇双乙醚二胺四乙酸（EGTA）等钙离子螯合剂以及D-600等钙离子通道阻滞剂，我们发现钙离子会深刻改变拮抗剂和激动剂与毒蕈碱受体的结合特性。在雌性大鼠中，钙离子对拮抗剂结合的影响主要体现在受体的最大结合容量上，而解离常数的变化则较为温和。这种影响表现为钙离子根据发情周期暴露或消除结合位点的能力。在激动剂结合方面，钙离子的存在对高亲和力结合位点的比例有显著影响，这与发情周期中拮抗剂结合所诱导的变化相似。有趣的是，从动情后期2到发情期的周期自然进展与体外去除钙离子时发生的变化相同。D-600可以完全阻断钙离子对[3H]-4NMPB和氧化震颤素结合的影响。诱导这种阻断所需的D-600浓度也取决于发情周期。发情周期的进展似乎伴随着毒蕈碱受体的变化，而这些变化可能反过来与钙离子通道相关联。
