Glucose transporters.

The recent cloning of families of glucose transporters has made it possible to study their structure and their role in an increasing number of disease states. Two classes of glucose transporters transfer glucose across the plasma membrane of human cells. In epithelial cells lining the jejunum and proximal renal tubules, Na+/glucose cotransporters concentrate glucose inside cells using the transmembrane electrochemical potential of Na+. Molecular defects of different transporters of this class cause familial glucose-galactose malabsorption and renal glycosuria. In the basolateral membrane of epithelial cells and in nonepithelial cells, glucose flows down its concentration gradient through a family of facilitative glucose transporters. Reduced numbers of different facilitative glucose transporters may contribute to both defective insulin secretion and insulin resistance in diabetes mellitus and to neurological diseases associated with decreased cerebrospinal fluid glucose.