title: Characterization of a snake venom neurotoxin which blocks nicotinic transmission in the avian ciliary ganglion.
abstract: Bungarus multicinctus venom was fractionated by ion exchange chromatography and the various fractions were assayed for their ability to block synaptic transmission through the chick ciliary ganglion. alpha-Bungarotoxin purified from this venom failed to block transmission at 50 micrograms/ml. A second neurotoxin, which we designate Toxin F, blocked transmission at 1-3 micrograms/ml and also blocked ganglionic depolarizations induced by carbachol. Toxin F was clearly distinguishable from alpha-bungarotoxin on the basis of molecular weight (estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis) and isoelectric point. Binding assays revealed that 125I-labeled toxin F bound to two sites in the ciliary ganglion: one site that was shared by alpha-bungarotoxin and toxin F and another site that was recognized solely by toxin F. Carbachol and d-tubocurarine displaced only that [125I]toxin F bound to the shared site and had no effect on [125I]toxin F bound to the site recognized by toxin F alone. The results suggest that toxin F blocks synaptic transmission in the chick ciliary ganglion by a postsynaptic mechanism. Further study is required to determine whether this effect of toxin F is mediated through a direct interaction with ganglionic nicotinic receptors.
mesh_terms: D000818:Animals; D001665:Binding Sites; D002038:Bungarotoxins / Q000302:isolation & purification / Q000378:metabolism / Q000494:pharmacology*; D002645:Chickens; D002924:Ciliary Body / Q000294:innervation*; D003864:Depression, Chemical; D004591:Electrophoresis, Polyacrylamide Gel; D005726:Ganglia, Parasympathetic / Q000187:drug effects*; D009498:Neurotoxins / Q000302:isolation & purification / Q000494:pharmacology*; D011978:Receptors, Nicotinic / Q000187:drug effects; D030162:Reptilian Proteins; D012910:Snake Venoms / Q000302:isolation & purification / Q000494:pharmacology*; D009435:Synaptic Transmission / Q000187:drug effects*
chemical_list: D002038:Bungarotoxins; D009498:Neurotoxins; D011978:Receptors, Nicotinic; D030162:Reptilian Proteins; D012910:Snake Venoms; C041907:snake venom neurotoxin F