Ligand binding to muscarinic receptors in intact longitudinal muscle strips from guinea-pig intestine.

1 The binding of ligands to muscarinic receptors in intact longitudinal muscle strips from guinea-pig small intestine has been determined by measuring the inhibition of the irreversible binding of [3H]-propylbenzilylcholine mustard ([3H]-PrBCM). 2 The IC50 values for inhibition of [3H]-PrBCM binding by a given ligand were generally higher in intact strips than those reported for broken-cell preparations. This effect is probably due, at least in part, to the presence of an access-limitation factor in the kinetics of the irreversible binding of [3H]-PrBCM to the intact tissue. 3 The mean Hill coefficients for antagonist binding approached unity, but those for strong agonists were significantly less than unity. There was, with the possible exceptions of hexyltrimethylammonium and oxotremorine, reasonably good agreement with the Hill coefficients reported for brain homogenates.