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

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Abstract
Primary cultures and membranes fractions from chick embryo retina bind iodinated α‐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°C is 1.76 × 105 M−1s−1, the dissociation rate constant (k−1) at 37°C is 1.15 × 10−1s−1. Nicotinic cholinergic ligands and local anaesthetics inhibit α‐bungarotoxin binding. In the case of carbamoylcholine, the inhibition of binding depends on the time of exposure to this cholinergic agonist. α‐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 α‐bungarotoxin receptor crossreacts with antisera raised against nicotinic acetylcholine receptors from Torpedo marmorata. These results are interpreted as indicating that α‐bungarotoxin binds to retinal nicotinic acetylcholine receptors without affecting cholinergic receptor function.