Citrate transport by the kidney and intestine

Citrate is an important metabolite that is transported in the kidney and intestine. Low urinary citrate concentrations, which may be determined in part by transport processes in the kidney, are associated with the development of kidney stones. Citrate is reabsorbed from the tubular filtrate in the renal proximal tubule on a sodium-coupled transporter, the Na+/dicarboxylate cotransporter, with a broad substrate specificity for Krebs cycle intermediates. The same transporter is found on the brush-border membrane of enterocytes. In contrast to the well-characterized apical pathway for citrate, there is relatively little information about citrate transport across the basolateral membrane. Recently, the complementary DNAs coding for the Na+/citrate transporters from the apical membranes of rabbit and human kidney, NaDC-1 and hNaDC-1, have been cloned and sequenced. These transporters belong to a separate gene family that includes the renal Na+/sulfate cotransporter, NaSi-1.