The opossum kidney cell type IIa Na/P(i) cotransporter is a phosphoprotein

Kidney Blood Press Res. 2001;24(1):1-4. doi: 10.1159/000054198.


Background/aim: Parathyroid hormone (PTH)-dependent inhibition of proximal tubular P(i) reabsorption is mediated by protein kinase A and/or C and is associated with reduced border membrane expression of the type IIa Na/P(i) cotransporter. The aim of this study was to analyze phosphorylation of the type IIa cotransporter protein.

Methods: Opossum kidney cells were used as a 'proximal tubular' cell model. Protein phosphorylation was determined by immunoprecipitation of the type IIa Na/P(i) cotransporter, followed by autoradiography. The transporter protein content was evaluated by Western blotting and transport activity by tracer P(i) uptake.

Results: Under control conditions (no PTH) the transporter was phosphorylated; upon treatment with PTH, a decrease in phosphorylation was observed. A protein phosphatase inhibitor (okadaic acid) was unable to prevent PTH-induced Na/P(i) cotransporter inhibition but reduced transporter degradation.

Conclusion: The type IIa Na/P(i) cotransporter is a phosphoprotein, but alterations in its phosphorylation seem not to be involved in P(i) transport inhibition.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Carrier Proteins / analysis
  • Carrier Proteins / metabolism*
  • Cells, Cultured
  • Kidney Tubules, Proximal / metabolism*
  • Opossums
  • Phosphoproteins / analysis
  • Phosphoproteins / metabolism*
  • Sodium-Phosphate Cotransporter Proteins
  • Symporters*


  • Carrier Proteins
  • Phosphoproteins
  • Sodium-Phosphate Cotransporter Proteins
  • Symporters