Portugal Camila Cabral, Miya Vivian Sayuri, Calaza Karin da Costa, Santos Rochelle Alberto Martins, Paes-de-Carvalho Roberto
Department of Neurobiology and Program of Neurosciences, Institute of Biology, Fluminense Federal University, Niterói, Brazil.
J Neurochem. 2009 Jan;108(2):507-20. doi: 10.1111/j.1471-4159.2008.05786.x. Epub 2008 Nov 17.
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.
维生素C在大脑中通过抗坏血酸钠协同转运蛋白2（SVCT - 2）转运抗坏血酸盐，通过葡萄糖转运蛋白转运脱氢抗坏血酸盐。在此，我们研究了鸡视网膜细胞中SVCT - 2的表达以及[¹⁴C]抗坏血酸盐的摄取和释放。在大鼠和鸡视网膜中检测到了SVCT - 2免疫反应性，特别是在内侧无长突细胞和神经节细胞层的细胞中。相应地，SVCT - 2在培养的视网膜神经元中表达，但在神经胶质细胞中不表达。[¹⁴C]抗坏血酸盐的摄取是可饱和的，并且被磺吡酮或无钠培养基抑制，但不受抑制脱氢抗坏血酸盐转运的处理的影响。谷氨酸刺激的维生素C释放不受谷氨酸转运抑制剂L - β - 苏 - 苄基天冬氨酸的抑制，这表明维生素C的释放不是由谷氨酸摄取介导的。此外，抗坏血酸盐对[³H]D - 天冬氨酸的释放没有影响，排除了谷氨酸/抗坏血酸盐交换机制。2 - 羧基 - 3 - 羧甲基 - 4 - 异丙烯基吡咯烷（ kainate）或N - 甲基 - D - 天冬氨酸（NMDA）刺激了释放，其作用被各自的拮抗剂6,7 - 二硝基喹喔啉 - 2,3 - 二酮（DNQX）或（5R,2S） - （1） - 5 - 甲基 - 10,11 - 二氢 - 5H - 二苯并[a,d]环庚烯 - 5,10 - 亚胺马来酸氢盐（MK - 801）阻断。然而，DNQX而非MK - 801或2 - 氨基 - 5 - 膦酰基戊酸（APV）阻断了谷氨酸的刺激。有趣的是，DNQX阻止了NMDA的刺激，这表明NMDA的作用是由谷氨酸释放和对非NMDA受体的刺激介导的。谷氨酸的作用既不依赖于细胞外钙，也不受细胞内钙螯合剂1,2 - 双（2 - 氨基苯氧基）乙烷 - N',N',N',N' - 四乙酸四钾盐（BAPTA - AM）的抑制，但被磺吡酮或无钠环境抑制。总之，视网膜细胞摄取和释放维生素C，可能是通过SVCT - 2，并且释放可被NMDA或非NMDA谷氨酸受体刺激。
