Ascorbic acid uptake to isolated nerve terminals and secretory granules from ox neurohypophyses

Isolated nerve terminals (neurosecretosomes) from cow neurohypophyses accumulated radioactivity when they were incubated with L[14C]-ascorbic acid in an ionic medium dominated by NaCl. Uptake of radioactivity was saturable with ascorbic acid concentration. Replacement of Na+ with Li+ in the incubation medium or presence of ouabain inhibited the accumulation. Isolated, purified cow neurosecretory granules contained 14 +/- 2 nmol ascorbate (n = 10) per mg of protein. When such granules were incubated with L[14C]-ascorbic acid in a KCl dominated medium, they took up radioactivity slowly. The accumulation was not saturable with ascorbic acid concentration and was not influenced by the presence of Mg2+ATP.