title: Neuromuscular blocking action of cadmium and manganese in isolated frog striated muscles.
abstract: In isolated frog sciatic nerve--gastrocnemius muscle preparations, exposure for 60 min to Cd2+ (0.1-2 mM) caused a marked attenuation of the twitch tension developed by stimulation of nerves but no or only a slight inhibition of the tension produced by direct stimulation at maximum twitch height. The inhibitory effect was partially reversed by 1 mM cysteine. In frog sartorius muscles, the addition of Cd2+ (0.1 mM) alos abolished the end-plate potential evoked by nerve stimulation but did not suppress potential changes induced by iontophoretically applied acetylcholine. The addition of Mn2+ (2 and 5 mM) attenuated the response of muscles to both direct and indirect stimulation; a greater attenuation of the latter was observed. The inhibition was not reserved by cysteine but was partially reversed by excess Ca2+. Contractile responses of frog rectus abdominis muscles to acetylcholine were not significantly affected by Cd2+ and Mn2+ but were attenuated by d-tubocurarine in a dose-dependent manner. Impulse conduction along sciatic nerves was not impaired by Cd2+ and Mn2+ but was by procaine. It appears that Cd2+ interferes with the release of acetylcholine from motor nerve terminals by reducing the transmembrane influxes of Ca2+, the influx possibly relating to SH groups of membrane constituents.
mesh_terms: D000109:Acetylcholine / Q000037:antagonists & inhibitors / Q000502:physiology; D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002104:Cadmium / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D005260:Female; D008297:Male; D008345:Manganese / Q000494:pharmacology*; D009046:Motor Neurons / Q000187:drug effects; D009411:Nerve Endings / Q000187:drug effects; D009466:Neuromuscular Blocking Agents; D009469:Neuromuscular Junction / Q000187:drug effects*; D011343:Procaine / Q000494:pharmacology; D009435:Synaptic Transmission / Q000187:drug effects*; D014403:Tubocurarine / Q000037:antagonists & inhibitors
chemical_list: D009466:Neuromuscular Blocking Agents; D002104:Cadmium; D008345:Manganese; D011343:Procaine; D000109:Acetylcholine; D014403:Tubocurarine