Ascorbic acid, an endogenous factor required for acetylcholine release from the synaptic vesicles.

The ACh-releasing factor, which is required for ACh release in presence of 2 mM ATP, 2 mM Mg and 10(-5) M Ca from isolated synaptic vesicles, was purified from the synaptosomal cytoplasm of rat brain by Sephadex G-15, DEAE-Sephadex, Sephadex G-10 and AG50W-2X column chromatographies and identified as ascorbic acid. A low concentration of L-ascorbic acid (5 x 10(-6) M) produced a release of ACh from the vesicles in the presence of ATP, MgCl2 and CaCl2, as did synaptosomal cytoplasm. This release of ACh induced by L-ascorbic acid was found to be dissociable from formation of lipid peroxide. These findings are discussed in relation to the physiological role of L-ascorbic acid in the brain.