Document Type

Article

Publication Date

Winter 2-1-2008

Abstract

The long-term effects of ouabain on transepithelial Na+ transport involve transcriptional downregulation of apical Na+/H+ exchanger isoform 3 (NHE3). The aim of this study was to determine whether ouabain could acutely regulate NHE3 via a posttranscriptional mechanism in LLC-PK1 cells. We observed that the basolateral, but not apical, application of ouabain for 1 h significantly reduced transepithelial Na+ transport. This effect was not due to changes in the integrity of tight junctions or increases in the intracellular Na+ concentration. Ouabain regulated the trafficking of NHE3 and subsequently inhibited its activity, a process independent of intracellular Na+ concentration. Ouabain-induced NHE3 trafficking was abolished by either cholesterol depletion or Src inhibition. Moreover, ouabain increased the intracellular Ca2+concentration. Pretreatment of cells with the intracellular Ca2+ chelator BAPTA-AM blocked ouabain-induced trafficking of NHE3. Also, blockade of Na+-K+-ATPase endocytosis by a phosphatidylinositol 3-kinase inhibitor was equally effective in attenuating ouabain-induced NHE3 trafficking. These data indicate that ouabain acutely stimulates NHE3 trafficking by activating the basolateral Na+-K+-ATPase signaling complex. Taken together with our previous observations, we propose that ouabain can simultaneously regulate basolateral Na+-K+-ATPase and apical NHE3, leading to inhibition of transepithelial Na+ transport. This mechanism may be relevant to proximal tubular Na+ handling during conditions associated with increases in circulating endogenous cardiotonic steroids.

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The version of record is available from the publisher at http://ajpcell.physiology.org/content/294/2/C555.full-text.pdf+html. Copyright © 2008 the American Physiological Society. All rights reserved.DOI:10.1152/ajpcell.00475.2007

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