Expression and regulation of the renal Na/phosphate cotransporter NaPi-IIa in a mouse model deficient for the PDZ protein PDZK1

Pflugers Arch. 2005 Jan;449(4):392-402. doi: 10.1007/s00424-004-1351-9. Epub 2004 Oct 29.


Inorganic phosphate (P(i)) is reabsorbed in the renal proximal tubule mainly via the type-IIa sodium-phosphate cotransporter (NaPi-IIa). This protein is regulated tightly by different factors, among them dietary P(i) intake and parathyroid hormone (PTH). A number of PDZ-domain-containing proteins have been shown to interact with NaPi-IIa in vitro, such as Na(+)/H(+) exchanger-3 regulatory factor-1 (NHERF1) and PDZK1. PDZK1 is highly abundant in kidney and co-localizes with NaPi-IIa in the brush border membrane of proximal tubules. Recently, a knock-out mouse model for PDZK1 (Pdzk1(-/-)) has been generated, allowing the role of PDZK1 in the expression and regulation of the NaPi-IIa cotransporter to be examined in in vivo and in ex vivo preparations. The localization of NaPi-IIa and other proteins interacting with PDZK1 in vitro [Na(+)/H(+) exchanger (NHE3), chloride-formate exchanger (CFEX)/putative anion transporter-1 (PAT1), NHERF1] was not altered in Pdzk1(-/-) mice. The abundance of NaPi-IIa adapted to acute and chronic changes in dietary P(i) intake, but steady-state levels of NaPi-IIa were reduced in Pdzk1(-/-) under a P(i) rich diet. This was paralleled by a higher urinary fractional P(i) excretion. The abundance of the anion exchanger CFEX/PAT1 (SLC26A6) was also reduced. In contrast, NHERF1 abundance increased in the brush border membrane of Pdzk1(-/-) mice fed a high-P(i) diet. Acute regulation of NaPi-IIa by PTH in vivo and by PTH and activators of protein kinases A, C and G (PKA, PKC and PKG) in vitro (kidney slice preparation) was not altered in Pdzk1(-/-) mice. In conclusion, loss of PDZK1 did not result in major changes in proximal tubule function or NaPi-IIa regulation. However, under a P(i)-rich diet, loss of PDZK1 reduced NaPi-IIa abundance indicating that PDZK1 may play a role in the trafficking or stability of NaPi-IIa under these conditions.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Blotting, Western
  • Cytoskeletal Proteins / metabolism
  • Diet
  • Female
  • Immunohistochemistry
  • In Vitro Techniques
  • Kidney / metabolism*
  • Kidney Tubules, Proximal / metabolism
  • Male
  • Membrane Proteins / genetics*
  • Membrane Proteins / physiology*
  • Mice
  • Mice, Knockout
  • Microvilli / metabolism
  • Phosphates / pharmacology
  • Phosphoproteins / metabolism
  • Protein Kinases / metabolism
  • Sodium-Hydrogen Exchangers
  • Sodium-Phosphate Cotransporter Proteins
  • Sodium-Phosphate Cotransporter Proteins, Type IIa
  • Symporters / biosynthesis*
  • Symporters / physiology*


  • Cytoskeletal Proteins
  • Membrane Proteins
  • Phosphates
  • Phosphoproteins
  • Slc34a1 protein, mouse
  • Sodium-Hydrogen Exchangers
  • Sodium-Phosphate Cotransporter Proteins
  • Sodium-Phosphate Cotransporter Proteins, Type IIa
  • Symporters
  • sodium-hydrogen exchanger regulatory factor
  • Protein Kinases