title: Glutamate receptors modulate sodium-dependent and calcium-independent vitamin C bidirectional transport in cultured avian retinal cells.
abstract: Vitamin C is transported in the brain by sodium vitamin C co-transporter 2 (SVCT-2) for ascorbate and glucose transporters for dehydroascorbate. Here we have studied the expression of SVCT-2 and the uptake and release of [(14)C] ascorbate in chick retinal cells. SVCT-2 immunoreactivity was detected in rat and chick retina, specially in amacrine cells and in cells in the ganglion cell layer. Accordingly, SVCT-2 was expressed in cultured retinal neurons, but not in glial cells. [(14)C] ascorbate uptake was saturable and inhibited by sulfinpyrazone or sodium-free medium, but not by treatments that inhibit dehydroascorbate transport. Glutamate-stimulated vitamin C release was not inhibited by the glutamate transport inhibitor l-beta-threo-benzylaspartate, indicating that vitamin C release was not mediated by glutamate uptake. Also, ascorbate had no effect on [(3)H] D-aspartate release, ruling out a glutamate/ascorbate exchange mechanism. 2-Carboxy-3-carboxymethyl-4-isopropenylpyrrolidine (Kainate) or NMDA stimulated the release, effects blocked by their respective antagonists 6,7-initroquinoxaline-2,3-dione (DNQX) or (5R,2S)-(1)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine hydrogen maleate (MK-801). However, DNQX, but not MK-801 or 2-amino-5-phosphonopentanoic acid (APV), blocked the stimulation by glutamate. Interestingly, DNQX prevented the stimulation by NMDA, suggesting that the effect of NMDA was mediated by glutamate release and stimulation of non-NMDA receptors. The effect of glutamate was neither dependent on external calcium nor inhibited by 1,2-bis (2-aminophenoxy) ethane-N',N',N',N',-tetraacetic acid tetrakis (acetoxy-methyl ester) (BAPTA-AM), an internal calcium chelator, but was inhibited by sulfinpyrazone or by the absence of sodium. In conclusion, retinal cells take up and release vitamin C, probably through SVCT-2, and the release can be stimulated by NMDA or non-NMDA glutamate receptors.
authors.affiliation: Department of Neurobiology and Program of Neurosciences, Institute of Biology, Fluminense Federal University, Niterói, Brazil.
authors.forename: Camila Cabral
authors.initials: CC
authors.lastname: Portugal
authors.forename: Vivian Sayuri
authors.initials: VS
authors.lastname: Miya
authors.forename: Karin da Costa
authors.initials: Kda C
authors.lastname: Calaza
authors.forename: Rochelle Alberto Martins
authors.initials: RA
authors.lastname: Santos
authors.forename: Roberto
authors.initials: R
authors.lastname: Paes-de-Carvalho
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001205:Ascorbic Acid / Q000378:metabolism*; D001224:Aspartic Acid / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D002614:Chelating Agents / Q000494:pharmacology; D002642:Chick Embryo; D003598:Cytoskeletal Proteins / Q000378:metabolism; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D018698:Glutamic Acid / Q000494:pharmacology; D016202:N-Methylaspartate / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D029363:Organic Anion Transporters, Sodium-Dependent / Q000378:metabolism; D051381:Rats; D017470:Receptors, Glutamate / Q000502:physiology*; D012160:Retina / Q000166:cytology*; D012964:Sodium / Q000378:metabolism*; D060347:Sodium-Coupled Vitamin C Transporters; D027981:Symporters / Q000378:metabolism; D046509:Tissue Culture Techniques; D014316:Tritium / Q000378:metabolism
chemical_list: D002614:Chelating Agents; D003598:Cytoskeletal Proteins; D018691:Excitatory Amino Acid Antagonists; D029363:Organic Anion Transporters, Sodium-Dependent; D017470:Receptors, Glutamate; D060347:Sodium-Coupled Vitamin C Transporters; D027981:Symporters; C120673:benzyloxyaspartate; D014316:Tritium; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester; D001224:Aspartic Acid; D018698:Glutamic Acid; D004533:Egtazic Acid; D016202:N-Methylaspartate; D012964:Sodium; D001205:Ascorbic Acid; D002118:Calcium