Is the contractile response to exogenous acetylcholine due to a presynaptic effect?
Whether the contractile response induced by exogenous acetylcholine (ACh) chiefly involved the pre- or post-synaptic junctional site of the motor endplate was studied by using the cat gastrocnemius nerve muscle preparation poisoned with beta-bungarotoxin (beta-BuTX), a toxin isolated from the venom of Bungarus multicinctus which acts presynaptically. 2 After neuromuscular transmission was completely blocked by beta-BuTX, the dose-response curve of the contractile response induced by close intra-arterial injection of ACh, was compared with that of the control. No appreciable difference was observed. 3 In contrast, the response to ACh was completely abolished when neuromuscular transmission was blocked by alpha-bungarotoxin, a toxin isolated from the same venom which acts postsynaptically. 4 It is concluded that postjunctional site of the motor end-plate is chiefly involved in the contractile response produced by exogenous ACh.
D000109:Acetylcholine / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D000818:Animals; D002038:Bungarotoxins / Q000494:pharmacology; D002415:Cats; D004558:Electric Stimulation; D005260:Female; D008297:Male; D009045:Motor Endplate / Q000187:drug effects*; D009119:Muscle Contraction / Q000187:drug effects*; D009469:Neuromuscular Junction / Q000187:drug effects* / Q000502:physiology; D009435:Synaptic Transmission / Q000187:drug effects
D002038:Bungarotoxins; D000109:Acetylcholine