Suppression by cholinesterase inhibition of a Ca(2+)-independent efflux of [3H]acetylcholine from the neuromuscular junction of the isolated rat diaphragm.

Abstract Endplate preparations of the left rat hemidiaphragm were incubated with [ 3 H]choline to label neuronal acetylcholine stores. Elevation of the concentration (13.5–135 mmol/l) of extracellular potassium chloride (KC1) stimulated the release of [ 3 H]acetylcholine in a concentration-dependent manner. KC1 (27 mmol/l) still caused a significant efflux of [ 3 H]acetylcholine in a Ca 2+ -free medium. Inhibitors of cholinesterase (physostigmine, diisopropylfluorophosphate) suppressed by 80% this Ca 2+ -independent efflux of [ 3 H]acetylcholine. Vesamicol (10 μmol/l), the blocker of the vesicular acetylcholine carrier, also suppressed the stimulated, Ca 2+ -independent efflux of [ 3 H]acet…