The transport properties of the human renal Na(+)- dicarboxylate cotransporter under voltage-clamp conditions.
The transport properties of the human Na(+)-dicarboxylate cotransporter, (hNaDC-1), expressed in Xenopus laevis oocytes were characterized using the two-electrode voltage clamp technique. Steady-state succinate-evoked inward currents in hNaDC-1 were dependent on the concentrations of succinate and sodium, and on the membrane potential. At -50 mV, the half-saturation constant for succinate (K(0.5)(succinate)) was 1.1 mM and the half-saturation constant for sodium (K(0.5)(sodium)) was 65 mM. The Hill coefficient was 2.3, which is consistent with a transport stoichiometry of 3 Na(+):1 divalent anion substrate. The hNaDC-1 exhibits a high-cation selectivity. Sodium is the preferred cation and other cations, such as lithium, were not able to support transport of succinate. The preferred substrates of hNaDC-1 are fumarate (K(0.5) 1.8 mM) and succinate, followed by methylsuccinate (K(0.5) 2.8 mM), citrate (K(0. 5) 6.8 mM) and alpha-ketoglutarate (K(0.5) 16 mM). The hNaDC-1 may also transport sodium ions through an uncoupled leak pathway, which is sensitive to phloretin inhibition. We propose a transport model for hNaDC-1 in which the binding of three sodium ions is followed by substrate binding.
Yao
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Department of Physiology and Biophysics, University of Texas Medical Branch, Galveston, Texas 77555-0641, USA.
Pajor
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D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002412:Cations / Q000378:metabolism / Q000494:pharmacology; D029382:Dicarboxylic Acid Transporters; D004553:Electric Conductivity; D006801:Humans; D007668:Kidney / Q000378:metabolism*; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D008845:Microinjections; D008954:Models, Biological; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism; D029363:Organic Anion Transporters, Sodium-Dependent; D018408:Patch-Clamp Techniques; D010693:Phloretin / Q000494:pharmacology; D018075:RNA, Complementary / Q000235:genetics / Q000378:metabolism; D012964:Sodium / Q000378:metabolism / Q000494:pharmacology; D013379:Substrate Specificity; D019802:Succinic Acid / Q000378:metabolism / Q000494:pharmacology; D027981:Symporters; D014982:Xenopus laevis
D002352:Carrier Proteins; D002412:Cations; D029382:Dicarboxylic Acid Transporters; D008565:Membrane Proteins; D029363:Organic Anion Transporters, Sodium-Dependent; D018075:RNA, Complementary; C092524:SLC13A2 protein, human; D027981:Symporters; D012964:Sodium; D019802:Succinic Acid; D010693:Phloretin