CLONING, FUNCTIONAL-CHARACTERIZATION, AND LOCALIZATION OF A RAT RENALNA-DICARBOXYLATE TRANSPORTER()

We report here the isolation, functional characterization, tissue dist ribution, and membrane localization of rat renal Na+-dicarboxylate tra nsporter (rNaDC-1). rNaDC-1 consists of 2,245 nucleotides, and the ded uced amino acid sequence showed 73% and 75% identity to rabbit and hum an NaDC-1, respectively. When expressed in Xenopus laevis oocytes, rNa DC-1 mediated sodium-dependent uptake of di- and tricarboxylates. Subs trates of rNaDC-1 evoked inward currents in oocytes expressed with rNa DC-1; succinate, alpha-ketoglutarate, and glutarate were relatively hi gh-affinity substrates, and citrate was a low-affinity substrate of rN aDC-1. The coupling ratio of citrate to charge was determined to be 1: 1 at pH 7.4; influx of one positive charge per citrate molecule sugges ts a symport of three Na+ with a divalent citrate. Expression of rNaDC -1 mRNA was detected in the kidney and the small and large intestines. Immunohistochemistry using polyclonal antibodies raised against the 1 4 amino acids at the COOH terminus of rNaDC-1 revealed that rNaDC-1 is localized exclusively in the luminal membrane of S2 and S3.