MAMMALIAN FACILITATIVE HEXOSE TRANSPORTERS MEDIATE THE TRANSPORT OF DEHYDROASCORBIC ACID

ALTHOUGH vitamin C is critical to human physiology1-5, it is not clear how it is taken up into cells. The kinetics of cell and tissue accumu lation of ascorbic acid in vitro indicate that the process is mediated by specific transporters at the cell membrane6. Some experimental obs ervations have linked the transport of ascorbic acid with hexose trans port systems in mammalian cells, although no clear information is avai lable regarding the specific role(s) of these transporters, if any, in this process7-16. Here we use the Xenopus laevis oocyte expression sy stem to show that the mammalian facilitative hexose transporters are e fficient transporters of the oxidized form of vitamin C (dehydroascorb ic acid). Two transport pathways, one with low affinity and one with h igh affinity for dehydroascorbic acid, were found in oocytes expressin g the mammalian transporters, and these oocytes accumulated vitamin C against a concentration gradient when supplied with dehydroascorbic ac id. We obtained similar results in experiments using normal human neut rophils. These observations indicate that mammalian facilitative hexos e transporters are a physiologically significant pathway for the uptak e and accumulation of vitamin C by cells, and suggest a mechanism for the accumulation of ascorbic acid against a concentration gradient.