Molecular Pharmacology, Vol 20, 519-525, Copyright © 1981 by the American Society for Pharmacology and Experimental Therapeutics

Phenoxybenzamine and Dibenamine Interactions with Calcium Channel Effectors of the Muscarinic Receptor

¹ Departments of Psychiatry and Pharmacology, Mayo Foundation, Rochester, Minnesota 55905

Phenoxybenzamine and dibenamine were more effective at blocking muscarinic acetylcholine receptor-mediated cyclic GMP formation in mouse neuroblastoma cells (clone N1E-115) than at blocking radiolabeled antagonist binding to the muscarinic receptors of these cells. High calcium concentrations antagonized the effects of these 2-halogenoethylamines on the cyclic GMP response but not on the receptor binding. In addition, the apparent equilibrium dissociation constant for carbachol and the muscarinic receptor determined in the biological assay with the use of the 2-halogenoethylamines was several-fold greater than that determined by radioligand binding assays. These results suggest that phenoxybenzamine and dibenamine interact with calcium channels in addition to muscarinic receptors, and on the basis of these and other results, we propose a scheme for the interactions of agonists and antagonists with muscarinic receptors and their effectors (calcium channels).