Glucose transporters of rat proximal tubule: differential expression and subcellular distribution

Abstract

In the late proximal tubule, glucose reabsorption progressively lowers the concentration of luminal glucose, and concentrative glucose influx increases to ensure complete glucose reabsorption. The change in glucose influx is effected by luminal Na(+)-dependent glucose transporters (Na(+)-GLUT), which exhibit higher Na(+)-to-glucose stoichiometric ratios in the late proximal tubule. In this work, the corresponding changes in the axial distribution of basolateral glucose efflux transporters (GLUTs) were examined. mRNAs encoding high-affinity facilitative basolateral transporter GLUT1, low-affinity GLUT2, and apical Na(+)-GLUT were identified in mixed populations of proximal convoluted and straight tubules. The organization of the cognate proteins was also appraised on Western blots. GLUT1 was present in glomeruli, proximal convoluted, and straight tubules, GLUT2 was only expressed in the proximal convoluted tubule, and Na(+)-GLUT was present in both proximal convoluted and straight segments. GLUT1 and GLUT2 were confined to the basolateral membrane, whereas Na(+)-GLUT was preferentially localized to the brush-border membrane. These data are consistent with the idea that glucose influx in early and late proximal tubule is achieved through Na(+)-GLUT, that GLUT1 and GLUT2 are responsible for glucose efflux in the early proximal tubule, and that in the late proximal tubule, where transcellular glucose flux is lower, only GLUT1 mediates glucose efflux.

Glucose entry into rat mesangial cells is mediated by both Na+-coupled and facilitative transporters

“…Our studies have shown that the mesangial cell Na+-coupled glucose transporter has close similarities to the carrier from epithelial cells in regard to its specificity of response to the Na + ion, capacity to promote the uptake of (z-methyl-glucoside and inhibition by phlorizin [9,19,21,[24][25][26]. The size of the co-transporte r transcript in the rat mesangial cells (2.2 kb) is similar not only to that of LLC-PK1 cells [21] but also to that reported for rat kidney cortex SGLT1 [29,30]. Furthermore its K m value is comparable to that observed in oocytes after injection of SGLT1 cRNA together with the cRNA of membrane-associated protein (RS1) from porcine kidney [31].…”

Streptozotocin diabetes and the expression of GLUT1 at the brush border and basolateral membranes of intestinal enterocytes

“…Quantitation of the bands revealed that BLM levels of GLUT1 were 78. 6 30.0 a.u. ), although the increase only reached statistical significance after 21 days (p < 0.02 compared to control) (Fig.…”

“…Although the protein is found in certain transporting cells e.g. renal proximal tubule and Caco-2 cells [6,7], there is, to date, no evidence for its expression in normal small intestinal epithelium [8]. In the present study we have used confocal immunofluorescence microscopy of rat jejunum, together with Western blotting of BBM and BLM prepared from intestinal mucosa, in order to examine the normal enterocyte distribution of *Corresponding author.…”

Reduced cortical renal GLUT1 expression induced by angiotensin-converting enzyme inhibition in diabetic spontaneously hypertensive rats

“…In the early S1 segment, where the bulk of filtered glucose is reabsorbed, the low affinity/ high capacity glucose transporters, SGLT2 and GLUT2 are co-expressed in the luminal brush border membrane and in the basolateral membrane, respectively. Increases in the cortical GLUT2 gene expression have been extensively reported in diabetes (9)(10)(11)(12)(13)(14)(15), and are important for renal glucose reabsorption maintenance in this condition, since high blood and interstitial glucose concentrations may lower the outwardly directed glucose gradient from tubule to blood (11). GLUT1 protein is also detected in the outer renal cortex, where it is not related to the tubule epithelial cells, but to the mesangial cells (16).…”