RENAL EPITHELIAL APICAL NA/P-I COTRANSPORTERS

Several mammalian renal Na-dependent transport systems for inorganic phosphate have recently been identified using oocytes of Xenopus laevis as an expression system. Expression of cloned transporters in oocytes resulted in Na/P-i cotransport activity with kinetic properties characteristic for proximal tubular apical Na/P-i cotransport. Sequence comparison suggests that renal Na/P-i cotransport systems cloned so far may belong to two different types/families of Na/P-i cotransporters. Localization of corresponding mRNAs and proteins revealed that both types of Na/P-i cotransporter systems are expressed in the apical membrane of proximal tubular cells. Evidence was obtained that one type of cloned renal Na/P-i cotransporter plays an important role in the physiological and pathophysiological regulation of renal P-i reabsorption.