title: Water transport by the renal Na(+)-dicarboxylate cotransporter.
abstract: This study investigated the ability of the renal Na(+)-dicarboxylate cotransporter, NaDC-1, to transport water. Rabbit NaDC-1 was expressed in Xenopus laevis oocytes, cotransporter activity was measured as the inward current generated by substrate (citrate or succinate), and water transport was monitored by the changes in oocyte volume. In the absence of substrates, oocytes expressing NaDC-1 showed an increase in osmotic water permeability, which was directly correlated with the expression level of NaDC-1. When NaDC-1 was transporting substrates, there was a concomitant increase in oocyte volume. This solute-coupled influx of water took place in the absence of, and even against, osmotic gradients. There was a strict stoichiometric relationship between Na(+), substrate, and water transport of 3 Na(+), 1 dicarboxylate, and 176 water molecules/transport cycle. These results indicate that the renal Na(+)-dicarboxylate cotransporter mediates water transport and, under physiological conditions, may contribute to fluid reabsorption across the proximal tubule.
authors.affiliation: Department of Physiology, University of California, School of Medicine, Los Angeles, California 90095-1751, USA. smeinild@mednet.ucla.edu
authors.forename: A K
authors.initials: AK
authors.lastname: Meinild
authors.forename: D D
authors.initials: DD
authors.lastname: Loo
authors.forename: A M
authors.initials: AM
authors.lastname: Pajor
authors.forename: T
authors.initials: T
authors.lastname: Zeuthen
authors.forename: E M
authors.initials: EM
authors.lastname: Wright
mesh_terms: D000818:Animals; D001693:Biological Transport, Active; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D029382:Dicarboxylic Acid Transporters; D003998:Dicarboxylic Acids / Q000378:metabolism; D005260:Female; D066298:In Vitro Techniques; D007668:Kidney / Q000378:metabolism*; D007687:Kidney Tubules, Proximal / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D009004:Monosaccharide Transport Proteins / Q000378:metabolism; D009865:Oocytes / Q000378:metabolism; D029363:Organic Anion Transporters, Sodium-Dependent; D009995:Osmosis; D011817:Rabbits; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D012964:Sodium / Q000378:metabolism; D051269:Sodium-Glucose Transporter 1; D027981:Symporters; D014867:Water / Q000378:metabolism*; D014982:Xenopus laevis
chemical_list: D002352:Carrier Proteins; D029382:Dicarboxylic Acid Transporters; D003998:Dicarboxylic Acids; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D009004:Monosaccharide Transport Proteins; D029363:Organic Anion Transporters, Sodium-Dependent; D011994:Recombinant Proteins; C092524:SLC13A2 protein, human; D051269:Sodium-Glucose Transporter 1; D027981:Symporters; D014867:Water; D012964:Sodium