Cramer S C, Pardridge W M, Hirayama B A, Wright E M
Department of Medicine, School of Medicine, University of California, Los Angeles 90024-1682.
Diabetes. 1992 Jun;41(6):766-70. doi: 10.2337/diab.41.6.766.
Glucose is reabsorbed from the glomerular filtrate in the proximal segment of the renal tubule in two stages. The first stage is uphill transport across the brush border membrane by Na(+)-glucose cotransport and the second stage is downhill transport across the basolateral membrane by facilitated diffusion. Genes for both a renal Na(+)-glucose cotransporter (SGLT1) and a renal facilitated glucose transporter (GLUT2) have been cloned and sequenced. To examine whether SGLT1 and GLUT2 colocalize to the same tubular epithelial cells in rat kidney, double-immunoperoxidase studies with dual chromogens and paraformaldehyde perfusion-fixed frozen sections of rat kidney were performed. Antipeptide antisera were prepared against rat GLUT2 (amino acids 510-522) and rabbit SGLT1 (amino acids 402-420). Proximal tubules were identified immunocytochemically with an antiserum raised against a synthetic peptide corresponding to the 21 amino acids at the COOH-terminal of the heavy chain of rat gamma-glutamyl transpeptidase, which is a proximal tubule-specific enzyme. The anti-GLUT2 antiserum strongly stained the basolateral membrane of 46% of cortical tubules, whereas the SGLT1 antiserum stained the brush border of 56% of the cortical tubules. The gamma-glutamyl transpeptidase antiserum also stained the brush border of 51% of the cortical tubules. GLUT2 and SGLT1 colocalized to 40% of cortical epithelium, but 16% of cortical epithelial cells were immunopositive for brush border SGLT1 and immunonegative for basolateral GLUT2. These gamma-glutamyl transpeptidase staining results suggest that at least 50% of the tubules in the cortex are proximal tubules and that SGLT1 and GLUT2 colocalize to most proximal tubules. The fact that SGLT1 antiserum immunoreacted with tubules unreactive to the GLUT2 antiserum suggests that either the SGLT1 epitope is conserved on a related brush border protein or that there is another GLUT transporter responsible for the exit of sugar from these proximal tubule cells.
葡萄糖在肾小管近端段从肾小球滤液中重吸收分两个阶段进行。第一阶段是通过钠-葡萄糖协同转运蛋白经刷状缘膜进行耗能转运，第二阶段是通过易化扩散经基底外侧膜进行顺浓度梯度转运。肾钠-葡萄糖协同转运蛋白（SGLT1）和肾易化葡萄糖转运蛋白（GLUT2）的基因均已被克隆和测序。为了检测SGLT1和GLUT2是否在大鼠肾脏的同一肾小管上皮细胞中共定位，采用双显色剂的双重免疫过氧化物酶研究方法，对经多聚甲醛灌注固定的大鼠肾脏冰冻切片进行检测。制备了针对大鼠GLUT2（氨基酸510 - 522）和兔SGLT1（氨基酸402 - 420）的抗肽抗血清。用针对与大鼠γ-谷氨酰转肽酶重链羧基末端21个氨基酸对应的合成肽产生的抗血清，通过免疫细胞化学方法鉴定近端小管，γ-谷氨酰转肽酶是一种近端小管特异性酶。抗GLUT2抗血清强烈染色46%的皮质小管的基底外侧膜，而SGLT1抗血清染色56%的皮质小管的刷状缘。γ-谷氨酰转肽酶抗血清也染色51%的皮质小管的刷状缘。GLUT2和SGLT1在40%的皮质上皮中共定位，但16%的皮质上皮细胞对刷状缘SGLT1免疫阳性而对基底外侧GLUT2免疫阴性。这些γ-谷氨酰转肽酶染色结果表明，皮质中至少50%的小管是近端小管，且SGLT1和GLUT2在大多数近端小管中共定位。SGLT1抗血清与对GLUT2抗血清无反应的小管发生免疫反应，这一事实表明，要么SGLT1表位在相关的刷状缘蛋白上保守，要么存在另一种GLUT转运蛋白负责这些近端小管细胞中糖的输出。
