Ehlert F J, Tran L P
Department of Pharmacology, College of Medicine, University of California, Irvine.
J Pharmacol Exp Ther. 1990 Dec;255(3):1148-57.
The distribution of subtypes of the muscarinic receptor in homogenates of the rat brain was investigated by measuring the competitive inhibition of the binding [3H]N-methylscopolamine by pirenzepine and AF-DX 116 (11[[2-[(diethylamino)methyl]-1-piperidinyl]acetyl]-5, 11-dihydro-6H-pyrido[2,3-b][1,4]benzodiazepine-6-one). In most brain regions, the competitive binding curves for AF-DX 116 and pirenzepine were consistent with a two-site model. The dissociation constant of pirenzepine for its high-affinity site (M1 receptor) was approximately 10(-8) M, whereas the dissociation constant of AF-DX 116 for its high affinity site (M2 receptor) was approximately 10(-7) M. In many regions, particularly those in the forebrain, the sum of the densities of the M1 and M2 binding sites was substantially less than 100% of the total sites, indicating the existence of a third population of sites lacking high affinity for both pirenzepine and AF-DX 116. We have designated these latter sites as non-M1, non-M2 muscarinic receptors. In general, the densities of the M1 and non-M1, non-M2 binding sites were highest in cerebral cortex, corpus striatum and hippocampus, intermediate in thalamus and hypothalamus, and lowest in midbrain, medulla-pons and cerebellum, whereas the M2 binding site had a relatively low, uniform density throughout the brain. The binding capacity of [3H]N-methylquinuclidinyl benzilate was estimated to be 20 to 30% lower than that of [3H]quinuclidinyl benzilate in various regions of the forebrain, but not in more caudal regions of the brain where the two radioligands had approximately the same binding capacities. Treatment of homogenates of the cerebral cortex with benzilylcholine mustard caused a selective loss of the majority of the [3H]N-methylscopolamine binding sites but spared 25% of the sites labeled by [3H]quinuclidinyl benzilate The results of pirenzepine/[3H]quinuclinyl benzilate competitive binding experiments on cerebral cortex treated with benzilylcholine mustard showed that the residual binding sites for [3H] quinuclidinyl benzilate were enriched in M1 muscarinic receptors.
通过测量哌仑西平和AF-DX 116（11[[2-[(二乙氨基)甲基]-1-哌啶基]乙酰基]-5,11-二氢-6H-吡啶并[2,3-b][1,4]苯并二氮杂䓬-6-酮）对[3H]N-甲基东莨菪碱结合的竞争性抑制作用，研究了大鼠脑匀浆中毒蕈碱受体亚型的分布。在大多数脑区，AF-DX 116和哌仑西平的竞争性结合曲线符合双位点模型。哌仑西平对其高亲和力位点（M1受体）的解离常数约为10(-8)M，而AF-DX 116对其高亲和力位点（M2受体）的解离常数约为10(-7)M。在许多区域，尤其是前脑区域，M1和M2结合位点密度之和显著低于总位点的100%，表明存在对哌仑西平和AF-DX 116均缺乏高亲和力的第三类位点。我们将这些后一类位点称为非M1、非M2毒蕈碱受体。一般来说，M1和非M1、非M2结合位点的密度在大脑皮层、纹状体和海马中最高，在丘脑和下丘脑中间，在中脑、延髓-脑桥和小脑中最低，而M2结合位点在整个大脑中的密度相对较低且均匀。在前脑的各个区域，[3H]N-甲基喹核醇基苯甲酸酯的结合能力估计比[3H]喹核醇基苯甲酸酯低20%至30%，但在脑的更尾端区域两者放射性配体的结合能力大致相同。用苯甲酰胆碱芥子碱处理大脑皮层匀浆导致大部分[3H]N-甲基东莨菪碱结合位点选择性丧失，但保留了25%的[3H]喹核醇基苯甲酸酯标记位点。对用苯甲酰胆碱芥子碱处理的大脑皮层进行哌仑西平/[3H]喹核醇基苯甲酸酯竞争性结合实验的结果表明，[3H]喹核醇基苯甲酸酯的残留结合位点富含M1毒蕈碱受体。
