ASCORBIC-ACID ACCUMULATION AND TRANSPORT IN HUMAN FIBROBLASTS

As the initial step in the use of fibroblasts as a model system for 'i n situ kinetics', ascorbic acid (vitamin C) accumulation in normal hum an fibroblasts was investigated for the first time. Ascorbic acid was transported into fibroblasts and accumulated against a concentration g radient up to 20-fold, as measured by h.p.l.c. with coulometric electr ochemical detection. Ascorbic acid accumulation was mediated by two co ncentration-dependent transport activities. The first was a high-affin ity activity with an apparent K(m) of 6 muM and an apparent V(max) of 203 muM/h, and the second was a low-affinity activity with an apparent K(m) of 5 mM and an apparent V(max) of 1.8 mM/h. Both activities were inhibited by metabolic inhibitors and inhibitors of ascorbic acid tra nsport in human neutrophils. The low-affinity transporter could not be accounted for by diffusion. Although the high-affinity transport acti vity was comparable with that described for human neutrophils, the low -affinity transporter was different. These data provide the first evid ence that two-component ascorbic acid transport may be a generalized m echanism for accumulation of this vitamin in humans.