Rodrigues de Miranda J F, Salden H J, van Ginneken C A
Department of Pharmacology, University of Nijmegen, The Netherlands.
Life Sci. 1987 Oct 26;41(17):2023-32. doi: 10.1016/0024-3205(87)90476-0.
The receptor occupancy-biological effect relationship for muscarinic receptors in guinea pig ileal smooth muscle has been studied by comparison of radioligand binding and contractile response. Muscarinic receptors in homogenates of ileal smooth muscle were labeled with [3H]-1-Quinuclidinyl benzilate. Treatment with propylbenzilylcholine mustard (PrBCM), to inactivate irreversibly muscarinic receptors, caused a large dose dependent rightward shift of the dose-response curve to three agonistic furtrethonium derivatives with a concomitant decrease in maximal response. Using those data, the fraction of receptors remaining unoccupied (q-values) and "true affinity constants" (-log KA-values) were calculated. Exposure to 20 or 60 nM PrBCM for 15 minutes resulted in a 39% and a 61% reduction in specific [3H]-1-Quinuclidinyl benzilate binding sites respectively to be compared with a 62% and a 85% decrease expected from calculated q-values. KA-values for the methyl and ethyl derivative agreed well with the dissociation constants for the high affinity agonist sites determined from displacement of [3H-]-1-Quinuclidinyl benzilate. The KA-value for the propylfurtrethonium corresponds to the low affinity agonist dissociation constant. The fraction of receptors in the high affinity agonist state differs considerably for the three furtrethonium derivatives investigated. Neither the fraction of receptors in the high affinity agonist state, nor the ratio of dissociation constants for these states is affected by the alkylation of 85% of the functional muscarinic receptors. The inactivation of components of the effector system by PrBCM seems unlikely.
通过比较放射性配体结合与收缩反应，研究了豚鼠回肠平滑肌中毒蕈碱受体的受体占有率与生物学效应的关系。用[3H]-1-喹核醇基苯甲酸酯标记回肠平滑肌匀浆中的毒蕈碱受体。用丙基苄基胆碱芥子碱（PrBCM）处理以不可逆地使毒蕈碱受体失活，导致对三种激动性呋氨硫铵衍生物的剂量反应曲线出现大的剂量依赖性右移，同时最大反应降低。利用这些数据，计算了未被占据的受体分数（q值）和“真实亲和常数”（-log KA值）。暴露于20或60 nM PrBCM 15分钟后，特异性[3H]-1-喹核醇基苯甲酸酯结合位点分别减少了39%和61%，与之相比，根据计算的q值预期减少62%和85%。甲基和乙基衍生物的KA值与通过[3H-]-1-喹核醇基苯甲酸酯置换测定的高亲和力激动剂位点的解离常数吻合良好。丙基呋氨硫铵的KA值对应于低亲和力激动剂解离常数。在所研究的三种呋氨硫铵衍生物中，处于高亲和力激动剂状态的受体分数有很大差异。无论是处于高亲和力激动剂状态的受体分数，还是这些状态的解离常数之比，都不受85%功能性毒蕈碱受体烷基化的影响。PrBCM使效应器系统成分失活的可能性似乎不大。
