Muscarinic cholinergic receptors in the retina of the larval tiger salamander.

The pharmacology and autoradiographic localization of muscarinic cholinergic receptors in retinal slices of the larval tiger salamander have been examined using the muscarinic antagonist [3H]propylbenzilylcholine mustard. Under the conditions of these experiments the binding of this ligand is irreversible. Saturation and maximum specific binding of 270 pM of ligand per gram protein are observed after an incubation of 1 h, and autoradiographic studies show that this does not reflect surface binding alone. Muscarinic but not nicotinic drugs suppress the binding of propylbenzilylcholine mustard at physiologically relevant concentrations; half-maximal suppression of binding by the muscarinic antagonists atropine sulfate and quinuclidinyl benzilate occurs, respectively, at 9.0 and 7.5 X 10(-10) M. Light microscopic autoradiography reveals the discrete localization of the ligand to the sites of synaptic contact, the retinal plexiform layers, predominantly the inner plexiform layer. The implications of the present study on current theories of cholinergic function in the vertebrate retina are discussed.