The renal Na+/phosphate cotransporter NaPi-IIa is internalized via the receptor-mediated endocytic route in response to parathyroid hormone

Kidney Int. 2006 Feb;69(3):495-503. doi: 10.1038/


The major renal Na(+)/phosphate cotransporter, NaPi-IIa, is regulated by a number of factors including parathyroid hormone (PTH), dopamine, and dietary phosphate intake. PTH induces the acute internalization of NaPi-IIa from the brush border membrane (BBM) and its routing to and subsequent degradation in lysosomes. Previous work indicated that megalin, part of the apical receptor-mediated endocytic apparatus, may play a role in the PTH-induced removal of NaPi-IIa. Here we examined in rats the time-dependent internalization route of NaPi-IIa after acute PTH application using immunohistochemistry and markers of several endocytic compartments. NaPi-IIa removal from the BBM was detectable as early as 5 min after PTH injection. After 10-15 min, NaPi-IIa was localized in subapical compartments positive for clathrin. Shortly thereafter, NaPi-IIa appeared in endosomes stained for EEA1 (early endosomal antigen 1). After 45-60 min, NaPi-IIa was found in late endosomes/lysosomes marked with lgp120. In contrast, no change in the subcellular localization of megalin and the Na(+)/H(+) exchanger NHE3 was detected up to 60 min after PTH injection. To further characterize the internalization route, insulin, as a marker for receptor-mediated endocytosis, and horseradish peroxidase (HRP) and fluorescein isothiocyanate (FITC)-dextran (10 kDa), as markers for fluid-phase mediated endocytosis, were used. NaPi-IIa colocalized with insulin 5-30 min after PTH injection but did not overlap with HRP or FITC-dextran. These results demonstrate a distinct internalization route of NaPi-IIa in response to acute PTH application that may involve the receptor-mediated endocytic pathway including clathrin-coated vesicles and EEA1-positive early endosomes, and routes NaPi-IIa to lysosomes for degradation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Clathrin / analysis
  • Coated Vesicles / chemistry
  • Coated Vesicles / physiology
  • Endocytosis / drug effects*
  • Endocytosis / physiology
  • Endosomes / chemistry
  • Endosomes / physiology
  • Fluorescent Antibody Technique
  • Immunohistochemistry / methods
  • Insulin / analysis
  • Insulin / physiology
  • Kidney / chemistry
  • Kidney / physiology
  • Low Density Lipoprotein Receptor-Related Protein-2 / analysis
  • Low Density Lipoprotein Receptor-Related Protein-2 / physiology
  • Lysosomes / chemistry
  • Lysosomes / physiology
  • Male
  • Parathyroid Hormone / administration & dosage
  • Parathyroid Hormone / pharmacology*
  • Rats
  • Rats, Wistar
  • Sodium-Hydrogen Exchanger 3
  • Sodium-Hydrogen Exchangers / analysis
  • Sodium-Hydrogen Exchangers / physiology
  • Sodium-Phosphate Cotransporter Proteins, Type IIa / metabolism*


  • Clathrin
  • Insulin
  • Low Density Lipoprotein Receptor-Related Protein-2
  • Parathyroid Hormone
  • Slc34a1 protein, rat
  • Slc9a3 protein, rat
  • Sodium-Hydrogen Exchanger 3
  • Sodium-Hydrogen Exchangers
  • Sodium-Phosphate Cotransporter Proteins, Type IIa