The sodium-dicarboxylate cotransporters (Solute carrier family 13) , which transport succinate and other Krebs cycle intermediates, fall into 2 categories based on their substrate affinity, low affinity and high affinity. Both the low- and high-affinity transporters play an important role in the handling of citrate by the kidneys. The two different Na+-coupled dicarboxylate transporters (NADC) have been identified in mammalian tissues. These are NADC1and NADC3 (NADC2 is found in C. Elegans). NADC1 is Na+-coupled, electrogenic, and exhibits low affinity for its dicarboxylatesubstrates. This isoform is expressedprimarily in the brush border membrane of intestinal and renalepithelial cells. The physiological function of NADC1 is to absorbthe intermediates of the citric acid cycle, such as citrate, succinate,-ketoglutarate, fumarate, and malate, in the intestine and kidney.NADC3 is also a Na+-coupled and electrogenic dicarboxylate transporter, but it exhibitsrelatively higher affinity for its substrates compared with NADC1.