Korcok Jasminka, Dixon S Jeffrey, Lo Theodore C Y, Wilson John X
Department of Physiology and Pharmacology, Faculty of Medicine and Dentistry, The University of Western Ontario, London, Ontario, Canada N6A 5C1.
Brain Res. 2003 Dec 12;993(1-2):201-7. doi: 10.1016/j.brainres.2003.09.016.
Skeletal muscle and brain are major sites of glucose transport and ascorbate (vitamin C) storage. Ascorbate is oxidized to dehydroascorbic acid (DHAA) when used as an enzyme cofactor or free radical scavenger. We evaluated the hypothesis that glucose regulates DHAA uptake and reduction to ascorbate (i.e., recycling) by skeletal muscle cells and cerebral astrocytes. DHAA uptake was inhibited partially by glucose added simultaneously with DHAA. Comparison of wild type L6 skeletal muscle cells with an L6-derived cell line (D23) deficient in facilitative hexose transporter isoform 3 (GLUT3), indicated that both GLUT3 and facilitative hexose transporter isoform 1 (GLUT1) mediate DHAA uptake. Preincubation of muscle cells with glucose inhibited the rates of glucose and DHAA uptake, and decreased the intracellular concentration of ascorbate derived from recycling of DHAA. In contrast, glucose preincubation did not depress GLUT1 protein and activity levels or DHAA recycling in astrocytes. These results establish that glucose downregulates subsequent recycling of DHAA by skeletal muscle cells but not astrocytes.
骨骼肌和大脑是葡萄糖转运和抗坏血酸（维生素C）储存的主要部位。当用作酶辅因子或自由基清除剂时，抗坏血酸会被氧化为脱氢抗坏血酸（DHAA）。我们评估了以下假设：葡萄糖调节骨骼肌细胞和脑星形胶质细胞对DHAA的摄取以及其还原为抗坏血酸（即再循环）的过程。与DHAA同时添加的葡萄糖会部分抑制DHAA的摄取。将野生型L6骨骼肌细胞与缺乏易化型己糖转运蛋白异构体3（GLUT3）的L6衍生细胞系（D23）进行比较，结果表明GLUT3和易化型己糖转运蛋白异构体1（GLUT1）均介导DHAA的摄取。用葡萄糖对肌肉细胞进行预孵育会抑制葡萄糖和DHAA的摄取速率，并降低源自DHAA再循环的细胞内抗坏血酸浓度。相反，葡萄糖预孵育不会降低星形胶质细胞中GLUT1的蛋白和活性水平，也不会降低DHAA的再循环。这些结果表明，葡萄糖会下调骨骼肌细胞而非星形胶质细胞对DHAA的后续再循环。
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