Status of glucose transporters in the mammalian kidney and renal development

Glucose is the main source of energy for the mammalian cells and its entry is mediated via various transporters. About 7 facilitative (GULT-1 to -7) a nd 2 concentrative glucose transporters (SGLT-1 and -2) have been identifie d: The facilitative glucose transporters allow the glucose entry into the c ell interior due to the concentration gradient and the latter via the Nam-d ependent electrochemical gradient. They have similar structural motifs with 12-14 putative transmembrane domains with a predicted protein size varying from 50 to 76 kDa. Some of the facilitative glucose transporters (GLUT-1, -2, -4 and -5) and both the sodium glucose co-transporters (SGLT-1 and -2) are expressed in the kidney. The transporters that are involved in the majo r transport of glucose in the kidney include GLUT-2 and SGLT-2. They are of high capacity and low affinity type and are expressed in the SI segment of the proximal tubule. All the transporters expressed in the kidney are deve lopmentally regulated. The mRNA expression of renal GLUTS is variable durin g the fetal and postnatal periods. On the other hand the mRNA of SGLTs incr eases steadily from the fetal period to maturity along with the increase in their functional activity, i.e,, glucose uptake. Recent studies indicate t hat the SGLTs are believed to selectively regulate tubulogenesis since they are expressed in the metanephric tubules very early in the embryonic life in mammals.