Na+-K+-ATPase that redistributes to apical membrane during ATP depletion remains functional

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Abstract

We have previously demonstrated using immunocytochemical, histochemical, and biochemical techniques that ischemia in vivo and ATP depletion in vitro result in dissociation of Na+-K+-adenosinetriphosphatase (ATPase) from the actin cytoskeleton and redistribution to the apical domain in renal proximal tubule cells. To directly evaluate whether apical Na+-K+-ATPase retained Na+ pumping activity, a rapidly reversible model of cellular ATP depletion in confluent LLC-PK1 cells grown on semipermeable membranes was utilized. Tight-junction integrity, monitored by electrical resistance, was lost during ATP depletion and reestablished during 2 h of ATP repletion. Total cellular Na+-K+-ATPase activity and total surface membrane [3H]ouabain binding remained constant, but specific apical [3H]ouabain binding increased (7 vs. 26 fmol/ filter, P < 0.01). Apical [3H]ouabain binding returned to base-line during 5 h of ATP repletion. Apically applied ouabain was then used to selectively inhibit apical Na+-K+-ATPase. It had no effect on apical-to-basolateral Na+ flux under physiological conditions (1.3 ± 0.61 vs. 1.27 ± 0.46 meq·filter-1·30 min-1), but it increased the apical-to-basolateral flux in ATP-depleted and then repleted monolayers (0.39 ± 0.12 vs. 0.83 ± 0.27 meq·filter-1·30 min-1, P < 0.01), implying that apical Na+-K+-ATPase retained Na+ pumping activity. Together, these data imply that ATP depletion induces loss of surface membrane polarity resulting in redistribution of functional proteins to the alternate domain.

Original languageEnglish (US)
Pages (from-to)F693-F697
JournalAmerican Journal of Physiology - Renal Fluid and Electrolyte Physiology
Volume265
Issue number5 34-5
DOIs
StatePublished - 1993

Keywords

  • Basolateral membrane
  • Ischemia
  • LLC-PK cells
  • Ouabain
  • Sodium transport

ASJC Scopus subject areas

  • Physiology

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