Molecular cloning, chromosomal organization, and functional characterization of a sodium-dicarboxylate cotransporter from mouse kidney.
The sodium-dicarboxylate cotransporter of the renal proximal tubule, NaDC-1, reabsorbs filtered Krebs cycle intermediates and plays an important role in the regulation of urinary citrate concentrations. (1) Low urinary citrate is a risk factor for the development of kidney stones. As an initial step in the characterization of NaDC-1 regulation, the genomic structure and functional properties of the mouse Na(+)-dicarboxylate cotransporter (mNaDC-1) were determined. The gene coding for mNaDC-1, Slc13a2, is found on chromosome 11. The gene is approximately 24.9 kb in length and contains 12 exons. The mRNA coding for mNaDC-1 is found in kidney and small intestine. Expression of mNaDC-1 in Xenopus laevis oocytes results in increased transport of di- and tricarboxylates. The Michaelis-Menten constant (K(m)) for succinate was 0.35 mM, and the K(m) for citrate was 0.6 mM. The transport of citrate was stimulated by acidic pH, whereas the transport of succinate was insensitive to pH changes. Transport by mNaDC-1 is electrogenic, and substrates produced inward currents in the presence of sodium. The sodium affinity was relatively high in mNaDC-1, with half-saturation constants for sodium of 10 mM (radiotracer experiments) and 28 mM at -50 mV (2-electrode voltage clamp experiments). Lithium acts as a potent inhibitor of transport, but it can also partially substitute for sodium. In conclusion, the mNaDC-1 is related in sequence and function to the other NaDC-1 orthologs. However, its function more closely resembles the rabbit and human orthologs rather than the rat NaDC-1, with which it shares higher sequence similarity.
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AM
Department of Physiology and Biophysics, University of Texas Medical Branch, Galveston, Texas 77555, USA. ampajor@utmb.edu
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D000818:Animals; D001692:Biological Transport / Q000187:drug effects / Q000235:genetics; D015152:Blotting, Northern; D002352:Carrier Proteins / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D002412:Cations / Q000378:metabolism; D002874:Chromosome Mapping; D002951:Citrates / Q000378:metabolism; D003001:Cloning, Molecular; D029382:Dicarboxylic Acid Transporters; D005091:Exons; D015870:Gene Expression / Q000502:physiology; D007438:Introns; D007668:Kidney / Q000737:chemistry* / Q000378:metabolism*; D008094:Lithium / Q000494:pharmacology; D008565:Membrane Proteins / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D051379:Mice; D008969:Molecular Sequence Data; D009865:Oocytes / Q000502:physiology; D029363:Organic Anion Transporters, Sodium-Dependent; D017434:Protein Structure, Tertiary; D012333:RNA, Messenger / Q000032:analysis; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity; D013329:Structure-Activity Relationship; D013386:Succinates / Q000378:metabolism; D027981:Symporters; D014982:Xenopus laevis
D002352:Carrier Proteins; D002412:Cations; D002951:Citrates; D029382:Dicarboxylic Acid Transporters; D008565:Membrane Proteins; D029363:Organic Anion Transporters, Sodium-Dependent; D012333:RNA, Messenger; C490479:Slc13a2 protein, mouse; C490478:Slc13a2 protein, rat; D013386:Succinates; D027981:Symporters; D008094:Lithium