Submitted on March 31, 2008
Revised on July 3, 2008
Accepted on July 16, 2008
Renal expression and localization of SLC9A3 sodium hydrogen exchanger and its possible role in acid-base regulation in freshwater trout (Oncorhynchus mykiss)
Goran Ivanis1, Marvin Braun1, and Steve F. Perry1*
1 University of Ottawa
* To whom correspondence should be addressed. E-mail: sfperry{at}uottawa.ca.
Experiments were performed to assess the possible involvement of the Na+/H+ exchanger isoform 3 (NHE3; SLC9A3) in renal acid-base regulation in adult rainbow trout (Oncorhynchus mykiss). NHE3 mRNA was expressed at high levels in the kidney relative to its paralog, NHE2. The results of in situ hybridization demonstrated an abundance of NHE3 mRNA in renal tubules. The combination of immunocytochemistry and histological staining revealed that NHE3 was confined to the apical membrane of proximal tubules where it was co-localized with the vacuolar type H+-ATPase (V-ATPase). Levels of NHE3 protein (assessed by western blotting) were increased during hypercapnia likely as a result of increased transcription as indicated by increasing levels of NHE3 mRNA (as determined by real time PCR). Plasma cortisol concentration was increased during hypercapnia and administration of exogenous cortisol caused a marked increase in NHE3 mRNA and protein. Thus, we speculate that the elevation of plasma cortisol during hypercapnia contributes to transcriptional activation of NHE3 that ultimately promotes acid-base regulation by stimulating H+ secretion and HCO3- reabsorption.
