Vesicular Storage and Release of Acetylcholine in Torpedo Electroplaque Synapses

The disposition of newly synthesized ACh subsequent to depletion of vesicular endogenous ACh by stimulation was studied in the electromotor nerve terminals of Torpedo marmorata using [ 3 H]acetate as a precursor of ACh. Little vesicular [ 3 H]ACh could be isolated from tissue immediately after stimulation at 1 Hz. After 3 h post‐stimulation recovery the newly synthesized [ 3 H]ACh is found predominantly in a subpopulation of vesicles distinct from the vesicles containing most of the endogenous poorly labelled ACh. Restimulation of the tissue causes release of highly labelled ACh with a specific radioactivity (SRA) comparable to that of the newly synthesized [ 3 H]ACh in the highly labelled subpopulation of vesicles and significantly greater than the SRA of ACh in the main vesicular pool or the total tissue.