Effects of phosphate intake on distribution of type II Na/Pi cotransporter mRNA in rat kidney

Kidney Int. 1999 Mar;55(3):976-83. doi: 10.1046/j.1523-1755.1999.055003976.x.


Background: Renal phosphate (Pi) reabsorption is regulated by dietary Pi intake, as well as in other ways. Changes in Pi reabsorption are associated with the modulation of sodium/Pi cotransporter type II (NaPi-2) protein abundance in the brush border membrane (BBM) of proximal tubules (PTs) and of renal NaPi-2 mRNA levels. In this study, we address whether the NaPi-2 protein and NaPi-2 mRNA distribution patterns in the renal cortex vary in parallel with changes of dietary Pi intake.

Methods: We investigated in cryosections of perfusion-fixed rat kidneys by in situ hybridization (ISH) and immunohistochemistry (IHC) the distribution patterns of NaPi-2 mRNA and of NaPi-2 protein one week, two hours, and four hours after changes in dietary Pi intake.

Results: NaPi-2 mRNA and NaPi-2 protein were present in PTs exclusively. In rats adapted to one week of high Pi intake, signals for NaPi-2 mRNA and NaPi-2 protein in cortical PTs were weak, except in the convoluted parts of PTs of juxtamedullary nephrons. After one week of low Pi intake, the ISH and IHC signals for NaPi-2 were high in PT segments in all cortical levels. The switch from a chronic high to a low Pi intake within two and four hours induced no increase and a slight increase, respectively, in the NaPi-2 mRNA signal in PTs of midcortical and of superficial nephrons, whereas in the BBM of these nephrons, NaPi-2 protein was markedly up-regulated. Two and four hours after switching from low to high Pi intake, the overall high ISH signal for NaPi-2 mRNA was unchanged, whereas NaPi-2 protein staining was drastically down-regulated in the BBM of PTs from superficial and midcortical nephrons.

Conclusions: The marked changes in NaPi-2 protein abundance in the BBM, following altered dietary Pi intake, precede corresponding changes at the RNA level by several hours. Thus, the early adaptation to altered Pi intake involves mRNA-independent mechanisms. The up- or down-regulation of NaPi-2 protein abundance in the BBM and NaPi-2 mRNA in PT affects mainly midcortical and superficial nephrons.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Carrier Proteins / classification
  • Carrier Proteins / genetics*
  • Carrier Proteins / metabolism
  • Diet
  • Immunohistochemistry
  • In Situ Hybridization
  • Kidney / metabolism*
  • Male
  • Phosphates / administration & dosage*
  • Phosphates / metabolism
  • RNA, Messenger / genetics*
  • RNA, Messenger / metabolism*
  • Rats
  • Rats, Wistar
  • Sodium / metabolism
  • Sodium-Phosphate Cotransporter Proteins
  • Sodium-Phosphate Cotransporter Proteins, Type II
  • Symporters*
  • Time Factors


  • Carrier Proteins
  • Phosphates
  • RNA, Messenger
  • Sodium-Phosphate Cotransporter Proteins
  • Sodium-Phosphate Cotransporter Proteins, Type II
  • Symporters
  • Sodium