Transport and stability of ascorbic acid in pituitary cultures

Ascorbic acid uptake in AtT-20 tumor cells and primary cultures of rat anterior and intermediate pituitary was sodium-dependent and showed half-maximal saturation between 9 and 18 microM ascorbate. When incubated in [14C]ascorbic acid at concentrations similar to those in serum (50 microM), all of the cells concentrated ascorbate 20- to 40-fold, producing intracellular ascorbate concentrations of 1-2 mM. HPLC analyses showed that over 90% of the intracellular label comigrated with authentic ascorbic acid. Although ascorbate was rapidly oxidized in culture medium in the absence of cells, incubation of ascorbate in culture medium in the presence of cells stabilized the ascorbate substantially. Unlike systems that transport dehydroascorbic acid, the ascorbate transport systems in all three preparations were not inhibited by glucose. Thus all three systems possess similar saturable, high-affinity, sodium-dependent active transport systems for ascorbic acid.