Chloride conductance and Pi transport are separate functions induced by the expression of NaPi-1 in Xenopus oocytes

J Membr Biol. 1998 Jul 1;164(1):71-7. doi: 10.1007/s002329900394.


Expression of the protein NaPi-1 in Xenopus oocytes has previously been shown to induce an outwardly rectifying Cl- conductance (GCl), organic anion transport and Na+-dependent Pi-uptake. In the present study we investigated the relation between the NaPi-1 induced GCl and Pi-induced currents and transport. NaPi-1 expression induced Pi-transport, which was not different at 1-20 ng/oocyte NaPi-1 cRNA injection and was already maximal at 1-2 days after cRNA injection. In contrast, GCl was augmented at increased amounts of cRNA injection (1-20 ng/oocyte) and over a five day expression period. Subsequently all experiments were performed on oocytes injected with 20 ng/oocytes cRNA. Pi-induced currents (Ip) could be observed in NaPi-1 expressing oocytes at high concentrations of Pi (>/= 1 mm Pi). The amplitudes of Ip correlated well with GCl. Ip was blocked by the Cl- channel blocker NPPB, partially Na+-dependent and completely abolished in Cl- free solution. In contrast, Pi-transport in NaPi-1 expressing oocytes was not NPPB sensitive, stronger depending on extracellular Na+ and weakly affected by Cl- substitution. Endogenous Pi-uptake in water-injected oocytes amounted in all experiments to 30-50% of the Na+-dependent Pi-transport observed in NaPi-1 expressing oocytes. The properties of the endogenous Pi-uptake system (Km for Pi > 1 mM; partial Na+- and Cl--dependence; lack of NPPB block) were similar to the NaPi-1 induced Pi-uptake, but no Ip could be recorded at Pi-concentrations </=3 mM. In summary, the present data suggest that Ip does not reflect charge transfer related to Pi-uptake, but a Pi-mediated modulation of GCl.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Biological Transport / genetics
  • Carrier Proteins / biosynthesis*
  • Carrier Proteins / genetics
  • Carrier Proteins / physiology*
  • Chloride Channels / metabolism*
  • Chlorides / physiology
  • Extracellular Space / chemistry
  • Gene Expression / drug effects
  • Ion Channel Gating / physiology*
  • Microinjections
  • Nitrobenzoates / pharmacology
  • Oocytes / metabolism*
  • Phosphates / metabolism*
  • RNA, Complementary / pharmacology
  • Sodium / physiology
  • Sodium-Phosphate Cotransporter Proteins
  • Symporters*
  • Xenopus


  • Carrier Proteins
  • Chloride Channels
  • Chlorides
  • Nitrobenzoates
  • Phosphates
  • RNA, Complementary
  • Sodium-Phosphate Cotransporter Proteins
  • Symporters
  • 5-nitro-2-(3-phenylpropylamino)benzoic acid
  • Sodium