Na+, Cl− cotransport in Ehrlich ascites tumor cells activated during volume regulation (regulatory volume increase)

Abstract

Ehrlich ascites cells were preincubated in hypotonic medium with subsequent restoration of tonicity. After the initial osmotic shrinkage the cells recovered their volume within 5 min with an associated KCl uptake. The volume recovery was inhibited when NO-3 was substituted for Cl-, and when Na+ was replaced by K+, or by choline (at 5 mM external K+). The volume recovery was strongly inhibited by furosemide and bumetanide, but essentially unaffected by DIDS. The net uptake of Cl- was much larger than the value predicted from the conductive Cl- permeability. The undirectional 36Cl flux, which was insensitive to bumetanide under steady-state conditions, was substantially increased during regulatory volume increase, and showed a large bumetanide-sensitive component. During volume recovery the Cl- flux ratio (influx/efflux) for the bumetanide-sensitive component was estimated at 1.85, compatible with a coupled uptake of Na+ and Cl-, or with an uptake via a K+,Na+,2Cl- cotransport system. The latter possibility is unlikely, however, because a net uptake of KCl was found even at low external K+, and because no K+ uptake was found in ouabain-poisoned cells. In the presence of ouabain a bumetanide-sensitive uptake during volume recovery of Na+ and Cl- in nearly equimolar amounts was demonstrated. It is proposed that the primary process during the regulatory volume increase is an activation of an otherwise quiescent, bumetanide-sensitive Na+,Cl- cotransport system with subsequent replacement of Na+ by K+ via the Na+/K+ pump, stimulated by the Na+ influx through the Na+,Cl- cotransport system.

Ca2+ sensitivity of volume‐regulatory K+ and Cl‐ channels in cultured human epithelial cells.

“…The RVI was, however, observed when an isotonic medium was applied to the cells which had been equilibrated with a hypotonic saline solution (Fig. 2 D), as found in other cell species (Roti Roti & Rothstein, 1973;Grinstein, Clarke & Rothstein, 1983;Hoffmann, Sjoholm & Simonsen, 1983;Roy & Sauve, 1987). This immediate shrinkage in response to an osmotic challenge with an isotonic saline solution implies that net reduction of intracellular osmoles occurred after attaining volume regulation under hypotonic conditions.…”

Ca(2+)‐dependent heat production by rat skeletal muscle in hypertonic media depends on Na(+)‐Cl‐ co‐transport stimulation.

“…It was shown recently that anion substitution of chloride suppresses hypertonic contractures (Bruton, 1989). Na+-Cl-co-transport activity is known to be enhanced during cellular regulatory volume increase in many types of cells (Hoffmann, Sjoholm & Simonsen, 1983;Geck & Pfeiffer, 1985;Hoffmann, 1987;Foskett, 1990) including isolated human muscle cells (Panet, Digregorio & Brown, 1987).…”

HgCI₂-lnduced Ion Transport Pathways in Ehrlich Ascites Tumor Cells

“…The supernatant was used for the determination of cellular Na+, K+ and CE. The results were corrected for extracellular medium trapped in the cell pellet (3H-inulin space) as described previously [19]. The pellet was used for determination of cell dry weight after cor rection for the PCA content (23% of the measured dry weight [18]).…”