EXPRESSION OF THE RENAL NA+ DICARBOXYLATE COTRANSPORTER NADC-1, IN COS-7 CELLS/

The cloned rabbit renal Na+/dicarboxylate cotransporter, NaDC-1, was t ransiently expressed in the mammalian monkey kidney cell line, COS-7. Cells transfected with the plasmid pSV-201, containing the cDNA for th e Na+/dicarboxylate cotransporter, expressed sodium-dependent succinat e and citrate transport after 48 h. Cells transfected with control pla smid, pSV-SPORT, did not express sodium-dependent transport of succina te or citrate. The transport of succinate in cells expressing NaDC-1 w as inhibited by di- and tricarboxylic acids, but not by monocarboxylic acids. Sodium-dependent transport of succinate was insensitive to cha nges in pH, while sodium-dependent citrate transport was stimulated by acidic pH. Succinate transport by NaDC-1 was saturable with an appare nt Michaelis constant, K-m, around 0.5 mM. The kinetics of sodium acti vation of succinate transport by NaDC-1 were sigmoidal, with an appare nt Hill coefficient of 2.9, indicating that three sodium ions are invo lved in the transport of each succinate. Succinate transport by NaDC-1 was inhibited by lithium. The functional characteristics of NaDC-1 ex pressed in COS-7 cells correspond to those of the Na+/dicarboxylate co transporter of the apical membrane of the renal proximal tubule.