Handbook of Vitamin C Research

In: Handbook of Vitamin C Research ISBN: 978-1-60741-874-0Editors: Hubert Kucharski and Julek Zajac©2009 Nova Science Publishers, Inc.Chapter VIIMolecular Bases of the CellularHandling of Vitamin CTransport and Metabolism in Health and DiseaseJ.J.G. Marin , M.A. Serrano, M.J. Perez 1 and R.I.R. MaciasLaboratory of Experimental Hepatology and Drug Targeting,1 Research Unit, University HospitalBiomedical Research Center for the Study of Liver and Gastrointestinal Diseases(CIBERehd), Instituto de Salud Carlos III,University of Salamanca, SpainAbstractUnder circumstances of an adequate dietary content in ascorbic acid the availabilityof this vitamin for cells is still not ensured. The reason could be poor intestinalabsorption or impaired access to cells in different tissues because, owing to the markedhydrophylicity of this molecule, the rate of free diffusion across plasma membranes islow. Indeed the role of carrier proteins in vitamin C uptake has been recently recognized.This was formerly believed to occur via passive transport, in which sugar carriersbelonging to the GLUT family were assumed to be involved. However, more recently ithas been described that ascorbic acid absorption by the intestine and uptake by cells fromthe blood requires more specific plasma membrane transporters for vitamin C as asubstrate and with the higher efficiency that is characteristic of active systems. In thiscase, the energy for active vitamin C uptake is provided by inwardly directed sodiumgradients. The differential tissue distribution of isoforms 1 and 2 of sodium-dependentvitamin C transporters (SVCT) accounts for the general and specific functions of theseContact Information: Jose J. G. Marin, Department of Physiology and Pharmacology, Campus Miguel deUnamuno E.I.D. S-09, 37007-Salamanca, Spain, Telephone: 34-923-294674, Fax: 34-923-294669, E-mail:jjgmarin@usal.es