Sodium-dependent ascorbic and dehydroascorbic acid uptake by SV-40-transformed retinal pigment epithelial cells.

The present data confirmed previous studies with other cell types that ascorbic acid and dehydroascorbic acid are transported through different transporters into SV-40-transformed retinal pigment epithelial cells. These experiments were performed on cells grown on 96-well culture plates. Ascorbic acid was taken up into the cell by a high-affinity transporter with Km = 0.041 mmol/l and a low Vmax of 2.74 pmol/min/well. Dehydroascorbic acid was taken up by a low-affinity transporter with Km = 5.67 mmol/l; however, the Vmax was 325.5 pmol/min/well. The uptake of both ascorbic acid and dehydroascorbic acid was dependent on the sodium concentration. The uptake of ascorbic acid does not involve oxidation-reaction steps because the uptake of [14C]-ascorbate was unaffected by the presence of an excess amount of unlabelled dehydroascorbic acid.