IMMUNOGOLD LOCALIZATION OF HIGH-AFFINITY GLUCOSE-TRANSPORTER ISOFORMSIN NORMAL RAT-KIDNEY

BACKGROUND: Facilitative glucose transporters (GLUT) have unique kinet ic characteristics and distributions suited to the functions of the ti ssues in which they reside. However, little is known about their indiv idual roles in renal glucose metabolism, and previous investigations o f renal GLUT expression have been extensive only with respect to their mRNA levels. We provide here a complete analysis of three GLUT isofor ms along the nephron using a sensitive immunodetection method. EXPERIM ENTAL DESIGN: Normal rat kidneys were harvested, fixed in paraformalde hyde, and embedded in either paraffin or resin as required for immunog old labeling of individual GLUT Isoforms 1, 3, and 4. Samples were eva luated by light microscopy and selected regions analyzed by high resol ution optical scanning with computer-assisted detection of immunogold- labeled GLUT at the subcellular level. We describe, compare, and relat e to the local patterns of glucose metabolism the cellular and subcell ular expression patterns of these GLUT along the nephron. RESULTS: GLU T1 was most intensely labeled in the medullary thick ascending limbs o f Henle, cortical collecting ducts, and inner medullary collecting duc ts. In contrast, GLUTS was most prominent in the inner medullary colle cting ducts and GLUT4 in medullary thick ascending limbs of Henle. All three GLUT were detected in glomerular tufts, and GLUT1 was also dete cted in parietal epithelial cells. The predominant subcellular distrib utions in tubule cells were: basolateral and basolateral/cytoplasmic f or GLUT1; basolateral and cytoplasmic for GLUT3; and perinuclear/cytop lasmic for GLUT4. GLUT 1 and 3 expressions were confirmed in specific regions by immunoblotting. CONCLUSIONS: 1) GLUT 1, 3, and 4 are expres sed in both glomeruli and renal tubules. 2) The unique GLUT expression patterns along the renal tubules suggests unique functional roles for these isoforms. 3) The renal cortex demonstrates lesser labeling inte nsity for the high-affinity GLUT compared with the medulla, where high er rates of glucose oxidation and glycolytic metabolism are paralleled by higher GLUT labeling intensities.