Suppression by cholinesterase inhibition of a Ca(2+)-independent efflux of [3H]acetylcholine from the neuromuscular junction of the isolated rat diaphragm.
Endplate preparations of the left rat hemidiaphragm were incubated with [3H]choline to label neuronal acetylcholine stores. Elevation of the concentration (13.5-135 mmol/l) of extracellular potassium chloride (KCl) stimulated the release of [3H]acetylcholine in a concentration-dependent manner. KCl (27 mmol/l) still caused a significant efflux of [3H]acetylcholine in a Ca(2+)-free medium. Inhibitors of cholinesterase (physostigmine, diisopropylfluorophosphate) suppressed by 80% this Ca(2+)-independent efflux of [3H]acetylcholine. Vesamicol (10 mumol/l), the blocker of the vesicular acetylcholine carrier, also suppressed the stimulated, Ca(2+)-independent efflux of [3H]acetylcholine. The inhibitory effect of physostigmine was not prevented by muscarine or nicotine receptor antagonists, but the inhibitory effect was lost when the stimulus strength was increased (81 mmol/l KCl). The present experiments showed cholinesterase inhibition to suppress a Ca(2+)-independent efflux of [3H]acetylcholine, probably by interference with a membrane-bound acetylcholine carrier.
Wessler
I
I
Department of Pharmacology, University of Mainz, Germany.
Wagner
G
G
Walczok
A
A
D000109:Acetylcholine / Q000032:analysis / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000502:physiology*; D002794:Choline / Q000032:analysis; D002800:Cholinesterase Inhibitors / Q000494:pharmacology*; D003964:Diaphragm; D005260:Female; D066298:In Vitro Techniques; D008297:Male; D009469:Neuromuscular Junction / Q000378:metabolism*; D010830:Physostigmine / Q000494:pharmacology; D010880:Piperidines / Q000494:pharmacology; D011189:Potassium Chloride / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D014316:Tritium
D002800:Cholinesterase Inhibitors; D010880:Piperidines; D014316:Tritium; C006189:vesamicol; D011189:Potassium Chloride; D010830:Physostigmine; D002794:Choline; D000109:Acetylcholine; D002118:Calcium