Muscarinic Cholinergic Receptors on the Endothelium of Human Cerebral Arteries

To characterize the muscarinic cholinergic receptors on the endothelium of human cerebral arteries, isometric tension measurement and receptor autoradiographic studies were performed. Acetylcholine (ACh) induced dose-dependent relaxation of human cerebral arteries precontracted by 10 −5 M serotonin, with an EC 50 of 1.9 ± 0.6 × 10 −6 M (n = 7). The relaxation was abolished by 10 −5 M hemoglobin. Autoradiography, using the muscarinic antagonist [ 3 H]propylbenzilylcholine mustard, demonstrated the high density of muscarinic cholinergic receptors on the endothelial cells of human cerebral arteries, especially on the luminal surface of the endothelium. These findings suggest that ACh-induced relaxation mediated by muscarinic cholinergic receptors on the endothelium has a physiological function in human cerebral arteries.