Glutamate receptors modulate sodium-dependent and calcium-independent vitamin C bidirectional transport in cultured avian retinal cells.
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.
Portugal
Camila Cabral
CC
Department of Neurobiology and Program of Neurosciences, Institute of Biology, Fluminense Federal University, Niterói, Brazil.
Miya
Vivian Sayuri
VS
Calaza
Karin da Costa
Kda C
Santos
Rochelle Alberto Martins
RA
Paes-de-Carvalho
Roberto
R
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
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