[Transepithelial transport of glucose].

Epithelia serve as barriers among various compartments in the body. Transepithelial transport of glucose across the barrier epithelial layer is mediated by membrane proteins called glucose transporters. Two types of glucose transporters have been identified: Na(+)-dependent glucose cotransporters (SGLT family), and facilitated-diffusion glucose transporters (GLUT family). These transporters play important roles in the sugar absorption in the intestinal epithelium, sugar reabsorption in the kidney tubule cells, and transfer of glucose across the blood-tissue barriers. In addition to glucose transporters, connexins of gap junctions mediate the transfer of glucose in the double-epithelial cell layer found in the ciliary body and the rat placenta. Polarized localization of transporters and connexins is the structural basis of the vectorial transfer of sugars across the barrier epithelial cell layers. Various techniques of molecular and cell biology have been applied to elucidate the molecular mechanism of such polarized localization.