Electrophysiological analysis of Na+/Pi cotransport mediated by a transporter cloned from rat kidney and expressed in Xenopus oocytes.
Phosphate (Pi) reabsorption in renal proximal tubules involves Na+/Pi cotransport across the brush border membrane; its transport rate is influenced by the Na(+)-coupled transport of other solutes as well as by pH. In the present study, we have expressed a cloned rat renal brush border membrane Na+/Pi cotransporter (NaPi-2) in Xenopus laevis oocytes and have analyzed its electrophysiologic properties in voltage- and current-clamp studies. Addition of Pi to Na(+)-containing superfusates resulted in a depolarization of the membrane potential and, in voltage-clamped oocytes, in an inward current (IP). An analysis of the Na+ and/or Pi concentration dependence of IP suggested a Na+/Pi stoichiometry of 3:1. IP was increased by increasing the pH of the superfusate; this phenomenon seems to be mainly related to a lowering of the affinity for Na+ interaction by increasing H+ concentration. The present data suggest that known properties of Pi handling at the tubular/membrane level are "directly" related to specific characteristics of the transport molecule (NaPi-2) involved.
Busch
A
A
Institute of Physiology I, Eberhard-Karls-Universität Tübingen, Germany.
Waldegger
S
S
Herzer
T
T
Biber
J
J
Markovich
D
D
Hayes
G
G
Murer
H
H
Lang
F
F
D000818:Animals; D002352:Carrier Proteins / Q000096:biosynthesis / Q000378:metabolism*; D005260:Female; D006863:Hydrogen-Ion Concentration; D007668:Kidney / Q000378:metabolism*; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009865:Oocytes / Q000187:drug effects / Q000502:physiology*; D010710:Phosphates / Q000378:metabolism*; D018075:RNA, Complementary / Q000378:metabolism; D051381:Rats; D012964:Sodium / Q000378:metabolism* / Q000494:pharmacology; D050608:Sodium-Phosphate Cotransporter Proteins; D027981:Symporters; D014982:Xenopus laevis
D002352:Carrier Proteins; D010710:Phosphates; D018075:RNA, Complementary; D050608:Sodium-Phosphate Cotransporter Proteins; D027981:Symporters; D012964:Sodium