Characterization of the α‐Bungarotoxin Receptor in Chick‐Embryo Retina

Primary cultures and membranes fractions from chick embryo retina bind iodinated alpha-bungarotoxin, a highly selective ligand for nicotinic acetylcholine receptors from skeletal muscle and fish electric organ. The binding is saturable with an equilibrium dissociation constant (Kd) of 0.75 +/- 0.09 nM. The pseudo-first-order rate constant (k+1) for binding at 37 degrees C is 1.76 +/- 10(5) M-1 s-1, the dissociation rate constant (k-1) at 37 degrees C is 1.15 x 10(-4) s-1. Nicotinic cholinergic ligands and local anaesthetics inhibit alpha-bungarotoxin binding. In the case of carbamoylcholine, the inhibition of binding depends on the time of exposure to this cholinergic agonist. alpha-Bungarotoxin has no effect on the carbamoylcholine-induced stimulation in sodium permeability of cultured retinal neurons. On sucrose density gradients containing Triton X-100, the toxin binding site sediments with an apparent sedimentation coefficient of 10.5-11 S. Detergent-solubilized alpha-bungarotoxin receptor cross reacts with antisera raised against nicotinic acetylcholine receptors from Torpedo marmorata. These results are interpreted as indicating that alpha-bungarotoxin binds to retinal nicotinic acetylcholine receptors without affecting cholinergic receptor function.