Interaction of histrionicotoxin with the putative nicotinic acetylcholine receptor of the chick visual system.

The frog alkaloid histrionicotoxin inhibits neuromuscular transmission in a non-competitive fashion and is thought to bind to the ion channel region of the nicotinic acetylcholine receptor (nAChR) of skeletal muscle and fish electric organ. Here, the use of histrionicotoxin as a probe for the putative nAChR of the chick visual system was investigated. Histrionicotoxin inhibited the binding of [125I]alpha-bungarotoxin to synaptic membranes of optic lobe or of retina in a competitive manner (Ki = 6 +/- 3 microM). However, the number of displaceable membrane binding sites for the physiologically active derivative [3H]perhydrohistrionicotoxin was 20-100-fold higher than of [125I]alpha-bungarotoxin binding sites. Also, the binding of [3H]perhydrohistrionicotoxin to the membranes could be displaced by local anaesthetics and phencyclidine, but was insensitive to nicotinic-cholinergic ligands or to alpha-bungarotoxin. It is concluded that histrionicotoxins are not specific ligands for nAChR in the chick CNS.