Characterization of Na+/H+ exchanger NHE8 in cultured renal epithelial cells

Jianning Zhang, Ion Alexandru Bobulescu, Sunita Goyal, Peter S. Aronson, Michel G. Baum, Orson W. Moe

Research output: Contribution to journalArticle

29 Scopus citations

Abstract

NHE8 is expressed in the apical membrane of the proximal tubule and is predicted to be a Na+/H+ exchanger on the basis of its primary amino acid sequence. Functional characterization of native NHE8 in mammalian cells has not been possible to date. We screened a number of polarized renal cell lines for the plasma membrane Na+/H+ exchangers (NHE1, 2, 3, 4, and 8) and found only NHE1 and NHE8 transcripts in NRK cells by RT-PCR. NHE8 protein is expressed in the apical membrane of NRK cells as demonstrated by immunoblots, confocal fluorescent immunocytochemistry, and immunoelectron microscopy. NHE1, on the other hand, is expressed primarily in the basolateral membrane. Bilateral perfusion of NRK cells grown on permeable supports shows Na+/H+ exchange activity on both the apical and basolateral membranes. NHE8-specific small interfering RNA knocks down NHE8 protein expression but does not affect NHE1 protein levels. Knockdown of NHE8 protein is accompanied by a commensurate reduction in apical NHE activity, without altered basolateral NHE activity. Conversely, transfection of NHE1-specific small interfering RNA knocks down NHE1 protein expression without affecting NHE8 protein levels and reduces basolateral NHE activity without affecting apical NHE activity. NHE8 is the only apical membrane Na +/H+ exchanger in NRK cells. NHE8 activity is Na + dependent, displaying a cooperative sigmoidal relationship, and is highly sensitive to 5-(N-ethyl-n-isopropyl)-amiloride (EIPA). NRK cells provide a useful system where NHE8 can be studied in its native environment.

Original languageEnglish (US)
Pages (from-to)F761-F766
JournalAmerican Journal of Physiology - Renal Physiology
Volume293
Issue number3
DOIs
StatePublished - Sep 1 2007

Keywords

  • Proximal tubule
  • Sodium/hydrogen exchanger
  • Sodium/proton exchanger

ASJC Scopus subject areas

  • Physiology
  • Urology

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