Mechanistic Insights and Functional Determinants of the Transport Cycle of the Ascorbic Acid Transporter SVCT2

Godoy, Alejandro; Ormazábal, Valeska; Moraga-Cid, Gustavo; Zúñiga, Felipe; Sotomayor, Paula; Barra, Valeria; Vásquez, O Karla; Montecinos, Viviana P.; Mardones, Lorena; Gúzman, Catherine; Villagrán, Marcelo; Aguayo, Luis G.; Oñate, Sergio A.; Reyes, Alejandro; Cárcamo, Juan G.; Rivas, Coralia I.; Vera, Juan Carlos

doi:10.1074/jbc.m608300200

Cited by 95 publications

(108 citation statements)

References 31 publications

(49 reference statements)

Supporting

Mentioning

102

Contrasting

Unclassified

Order By: Relevance

“…(The order of intracellular substrate dissociation is assumed.) Each carrier state is identified by a number (1)(2)(3)(4)(5)(6)(7)(8) and by a prime denoting that the carrier is at the external face of the membrane or double prime indicating the internal face. A Na ϩ uniport pathway or "internal leak," also electroneutral (n H Na ϭ 1), is shown as step 2 3 7.…”

Section: Discussionmentioning

confidence: 99%

Transport model of the human Na⁺-coupled l-ascorbic acid (vitamin C) transporter SVCT1

Mackenzie¹,

Illing²,

Hediger³

2008

American Journal of Physiology-Cell Physiology

View full text Add to dashboard Cite

Mackenzie B, Illing AC, Hediger MA. Transport model of the human Na ϩ -coupled L-ascorbic acid (vitamin C) transporter SVCT1. Am J Physiol Cell Physiol 294: C451-C459, 2008. First published December 19, 2007 doi:10.1152/ajpcell.00439.2007.-Vitamin C (L-ascorbic acid) is an essential micronutrient that serves as an antioxidant and as a cofactor in many enzymatic reactions. Intestinal absorption and renal reabsorption of the vitamin is mediated by the epithelial apical L-ascorbic acid cotransporter SVCT1 (SLC23A1). We explored the molecular mechanisms of SVCT1-mediated L-ascorbic acid transport using radiotracer and voltage-clamp techniques in RNA-injected Xenopus oocytes. L-Ascorbic acid transport was saturable (K0.5 Ϸ 70 M), temperature dependent (Q10 Ϸ 5), and energized by the Na ϩ electrochemical potential gradient. We obtained a Na ϩ -L-ascorbic acid coupling ratio of 2:1 from simultaneous measurement of currents and fluxes. L-Ascorbic acid and Na ϩ saturation kinetics as a function of cosubstrate concentrations revealed a simultaneous transport mechanism in which binding is ordered Na ϩ , L-ascorbic acid, Na ϩ . In the absence of L-ascorbic acid, SVCT1 mediated pre-steady-state currents that decayed with time constants 3-15 ms. Transients were described by single Boltzmann distributions. At 100 mM Na ϩ , maximal charge translocation (Qmax) was Ϸ25 nC, around a midpoint (V0.5) at Ϫ9 mV, and with apparent valence ϷϪ1. Qmax was conserved upon progressive removal of Na ϩ , whereas V0.5 shifted to more hyperpolarized potentials. Model simulation predicted that the pre-steady-state current predominantly results from an ion-well effect on binding of the first Na ϩ partway within the membrane electric field. We present a transport model for SVCT1 that will provide a framework for investigating the impact of specific mutations and polymorphisms in SLC23A1 and help us better understand the contribution of SVCT1 to vitamin C metabolism in health and disease. cotransporters; sodium dependent; intestinal absorption; model simulation; renal reabsorption; Xenopus oocyte VITAMIN C (L-ascorbic acid) is an essential micronutrient that serves as an antioxidant scavenger of free radicals and as a cofactor in many enzymatic reactions (3,6,10,26,29). It cannot be synthesized in Homo sapiens and must be derived from the diet. Intestinal absorption and renal reabsorption of the vitamin is mediated by the epithelial Na ϩ -dependent Lascorbic acid cotransporter SVCT1 (reviewed in Refs. 32 and 35), the product of the SLC23A1 gene. Selective sorting of SVCT1 protein to the apical membrane has been demonstrated in cultured cell lines (Caco2 and MDCK) of intestinal and renal origin (2, 23).We and others previously demonstrated that human SVCT1 is a Na ϩ -dependent transporter that favors L-ascorbic acid over D-isoascorbic acid and that the oxidized form of vitamin C, dehydroascorbic acid, is excluded (5, 34). Here we explored its molecular mechanisms by testing the hypothesis that the Na ϩ dependence and rheogenicity of SVCT1 arise from...

show abstract

Section: Discussionmentioning

confidence: 99%

Transport model of the human Na⁺-coupled l-ascorbic acid (vitamin C) transporter SVCT1

Mackenzie¹,

Illing²,

Hediger³

2008

American Journal of Physiology-Cell Physiology

View full text Add to dashboard Cite

show abstract

“…L-ascorbate is transported against its concentration gradient ( Daruwala et al, 1999;Tsukaguchi et al, 1999), and thus the energy required for the transport is supplied by sodium exchange through the Na + /K + -ATPase pump (Castro et al, 2001). The relationship between sodium and ascorbate transport was found to be 2:1, and the order of union to the substrate was sodium-ascorbate-sodium (Godoy et al, 2007). At the molecular level, two SVCTs (SVCT1 and SVCT2) encoded by different genes have been described Figure 4.…”

Section: Vitamin C Transporters In the Brainmentioning

confidence: 99%

Typical and atypical stem cells in the brain, vitamin C effect and neuropathology

Nualart¹,

Salazar²,

Oyarce³

et al. 2012

Biol. Res.

View full text Add to dashboard Cite

Stem cells are considered a valuable cellular resource for tissue replacement therapies in most brain disorders. Stem cells have the ability to self-replicate and diff erentiate into numerous cell types, including neurons, oligodendrocytes and astrocytes. As a result, stem cells have been considered the "holy grail" of modern medical neuroscience. Despite their tremendous therapeutic potential, little is known about the mechanisms that regulate their diff erentiation. In this review, we analyze stem cells in embryonic and adult brains, and illustrate the diff erentiation pathways that give origin to most brain cells. We also evaluate the emergent role of the well known anti-oxidant, vitamin C, in stem cell diff erentiation. We believe that a complete understanding of all molecular players, including vitamin C, in stem cell diff erentiation will positively impact on the use of stem cell transplantation for neurodegenerative diseases.

show abstract

“…In the fi rst mechanism, vitamin C (ascorbic acid) is the specifi c substrate transported, by a high-affi nity, low-capacity system, that is sodium-and temperature-dependent (Daruwala et al, 1999;Tsukaguchi et al, 1999;Liang et al, 2002;Godoy et al, 2007). The molecular identity of this system has been delineated following cloning of two transporters (from human kidney cDNA library): the human sodium vitamin C cotransporters, SVCT1 and SVCT2 (products of the SLC23A2 and SLC23A1 genes, respectively; Daruwala et al, 1999).…”

Section: Vitamin C and Vitamin C Transportersmentioning

confidence: 99%

Vitamin C and oxidative stress in the seminiferous epithelium

et al. 2011

View full text Add to dashboard Cite

In this article, we focus on the fundamental role of vitamin C transporters for the normal delivery of vitamin C to germ cells in the adluminal compartment of seminiferous tubules. We argue that the redox status within spermatozoa or in semen is partly responsible for the etiology of infertility. In this context, antioxidant defence plays a critical role in male fertility. Vitamin C, a micronutrient required for a wide variety of metabolic functions, has long been associated with male reproduction. Two systems for vitamin C transport have been described in mammals. Facilitative hexose transporters (GLUTs), with 14 known isoforms to date, GLUT1-GLUT14, transport the oxidized form of vitamin C (dehydroascorbic acid) into the cells. Sodium ascorbic acid co-transporters (SVCTs), SVCT1 and SVCT2 transport the reduced form of vitamin C (ascorbic acid). Sertoli cells control germ cell proliferation and differentiation through cell-cell communication and form the blood-testis barrier. Because the blood-testis barrier limits direct access of molecules from the plasma into the adluminal compartment of the seminiferous tubule, one important question is the method by which germ cells obtain vitamin C. Some interesting results have thrown light on this matter. Expression of SVCT2 and some isoforms of GLUT transporters in the testis have previously been described. Our group has demonstrated that Sertoli cells express functionally active vitamin C transporters. Kinetic characteristics were described for both transport systems (SVCT and GLUT systems). Sertoli cells are able to transport both forms of vitamin C. These fi ndings are extremely relevant, because Sertoli cells may control the amount of vitamin C in the adluminal compartment, as well as regulating the availability of this metabolite throughout spermatogenesis.

show abstract

Mechanistic Insights and Functional Determinants of the Transport Cycle of the Ascorbic Acid Transporter SVCT2

Abstract: We characterized the human Na ؉ -ascorbic acid transporter SVCT2 and developed a basic model for the transport cycle that challenges the current view that it functions as a Na ؉ -dependent transporter.

Cited by 95 publications

References 31 publications

Transport model of the human Na⁺-coupled l-ascorbic acid (vitamin C) transporter SVCT1

Transport model of the human Na⁺-coupled l-ascorbic acid (vitamin C) transporter SVCT1

Typical and atypical stem cells in the brain, vitamin C effect and neuropathology

Vitamin C and oxidative stress in the seminiferous epithelium

Contact Info

Product

Resources

About

Mechanistic Insights and Functional Determinants of the Transport Cycle of the Ascorbic Acid Transporter SVCT2

Abstract: We characterized the human Na ؉ -ascorbic acid transporter SVCT2 and developed a basic model for the transport cycle that challenges the current view that it functions as a Na ؉ -dependent transporter.

Cited by 95 publications

References 31 publications

Transport model of the human Na+-coupled l-ascorbic acid (vitamin C) transporter SVCT1

Transport model of the human Na+-coupled l-ascorbic acid (vitamin C) transporter SVCT1

Typical and atypical stem cells in the brain, vitamin C effect and neuropathology

Vitamin C and oxidative stress in the seminiferous epithelium

Contact Info

Product

Resources

About

Transport model of the human Na⁺-coupled l-ascorbic acid (vitamin C) transporter SVCT1

Transport model of the human Na⁺-coupled l-ascorbic acid (vitamin C) transporter SVCT1