Characterization of muscarinic acetylcholine receptors in human penile corpus cavernosum: studies on whole tissue and cultured endothelium.

The binding characteristics of the muscarinic acetylcholine receptor antagonist, [3H]quinuclidinyl benzilate, to isolated membranes of human corpus cavernosum and endothelial cells, cultured from this tissue, were investigated. [3H]quinuclidinyl benzilate bound to membranes of human corpus cavernosum and endothelial cells with high affinity and limited capacity. Analysis of the binding data by Scatchard plot revealed the presence of one class of binding sites. The ligand binding specificity was determined by competitive binding assay. The data obtained show that [3H]quinuclidinyl benzilate was displaced by unlabeled competitors in the following order of efficacy in both membrane preparations: quinuclidinyl benzilate greater than scopolamine greater than atropine greater than 4-diphenylacetoxy-N-methyl-piperidine methiodide, M3 antagonist greater than pirenzepine, M1 antagonist greater than oxotremorine greater than (4-hydroxy-2-butynyl)trimethylammonium chloride m-chlorocarbanilate, M1 agonist greater than carbachol greater than hexamethonium. Solubilization of the muscarinic acetylcholine receptors from human corpus cavernosum and endothelial cells, with 1% digitonin and 0.02% cholate and subsequent analysis on sucrose density gradients, demonstrated the presence of a macromolecule specifically bound to [3H]quinuclidinyl benzilate sedimenting at the 6.2 S region of the gradient. These results demonstrate the presence of muscarinic acetylcholine receptors in human corpus cavernosum and in endothelial cells cultured from this tissue.