Renal phosphaturia during metabolic acidosis revisited: molecular mechanisms for decreased renal phosphate reabsorption.
Pflugers Arch
; 457(2): 539-49, 2008 Nov.
Article
in En
| MEDLINE
| ID: mdl-18535837
ABSTRACT
During metabolic acidosis (MA), urinary phosphate excretion increases and contributes to acid removal. Two Na(+)-dependent phosphate transporters, NaPi-IIa (Slc34a1) and NaPi-IIc (Slc34a3), are located in the brush border membrane (BBM) of the proximal tubule and mediate renal phosphate reabsorption. Transcriptome analysis of kidneys from acid-loaded mice revealed a large decrease in NaPi-IIc messenger RNA (mRNA) and a smaller reduction in NaPi-IIa mRNA abundance. To investigate the contribution of transporter regulation to phosphaturia during MA, we examined renal phosphate transporters in normal and Slc34a1-gene ablated (NaPi-IIa KO) mice acid-loaded for 2 and 7 days. In normal mice, urinary phosphate excretion was transiently increased after 2 days of acid loading, whereas no change was found in Slc34a1-/- mice. BBM Na/Pi cotransport activity was progressively and significantly decreased in acid-loaded KO mice, whereas in WT animals, a small increase after 2 days of treatment was seen. Acidosis increased BBM NaPi-IIa abundance in WT mice and NaPi-IIc abundance in WT and KO animals. mRNA abundance of NaPi-IIa and NaPi-IIc decreased during MA. Immunohistochemistry did not indicate any change in the localization of NaPi-IIa and NaPi-IIc along the nephron. Interestingly, mRNA abundance of both Slc20 phosphate transporters, Pit1 and Pit2, was elevated after 7 days of MA in normal and KO mice. These data demonstrate that phosphaturia during acidosis is not caused by reduced protein expression of the major Na/Pi cotransporters NaPi-IIa and NaPi-IIc and suggest a direct inhibitory effect of low pH mainly on NaPi-IIa. Our data also suggest that Pit1 and Pit2 transporters may play a compensatory role.
Full text:
1
Collection:
01-internacional
Database:
MEDLINE
Main subject:
Phosphates
/
Acidosis
/
Sodium-Phosphate Cotransporter Proteins, Type IIa
/
Hypophosphatemia, Familial
/
Kidney Tubules, Proximal
Type of study:
Prognostic_studies
Limits:
Animals
Language:
En
Journal:
Pflugers Arch
Year:
2008
Document type:
Article
Affiliation country:
Switzerland