Properties of electrogenic Pi transport by a human renal brush border Na+/Pi transporter.
Inorganic phosphate (Pi) induced an inward current (IP) in Xenopus oocytes expressing the human renal Na+/Pi cotransporter NaPi-3. At 100mM Na+, Pi-transport was independent of the holding potential and resulted in an apparent Km of 0.08 mM; lowering the Na+ concentration to 50 mM resulted in an increase of the apparent Km to 0.22 mM at -50 mV and to 0.31 mM at -90 mV. In contrast, the apparent Km for Na+ was not significantly influenced by the holding potential. A decrease of the pH from 7.8 to 6.8 resulted in a decrease of IP at 50 mM Na+, but not at 150 mM Na+. Arsenate induced inward currents through NaPi-3 and decreased the apparent Km in measurements of IP. Phosphonoformic acid itself induced no currents, but inhibited Pi-induced currents with an apparent Ki of 3.6 mM. In summary, NaPi-3 displays characteristic Na+/Pi cotransporter properties with relevant interactions with arsenate (transport substrate) and phosphonoformic acid (inhibitor). Monovalent and divalent Pi both appear to be transported by NaPi-3.
Busch
A E
AE
Institute of Physiology I, Eberhard-Karls-Universität Tübingen, Germany.
Wagner
C A
CA
Schuster
A
A
Waldegger
S
S
Biber
J
J
Murer
H
H
Lang
F
F
D000818:Animals; D001665:Binding Sites; D002352:Carrier Proteins / Q000378:metabolism*; D005260:Female; D006863:Hydrogen-Ion Concentration; D007687:Kidney Tubules, Proximal / Q000196:embryology / Q000378:metabolism*; D008564:Membrane Potentials; D009865:Oocytes / Q000378:metabolism; D018408:Patch-Clamp Techniques; D010710:Phosphates / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism; D050608:Sodium-Phosphate Cotransporter Proteins; D027981:Symporters; D014982:Xenopus laevis
D002352:Carrier Proteins; D010710:Phosphates; D050608:Sodium-Phosphate Cotransporter Proteins; D027981:Symporters; D012964:Sodium