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Am J Physiol Cell Physiol 270: C1277-C1283, 1996;
0363-6143/96 $5.00
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AJP - Cell Physiology, Vol 270, Issue 5 C1277-C1283, Copyright © 1996 by American Physiological Society

ARTICLES

Palytoxin modulates cytosolic pH in human osteoblast-like Saos-2 cells via an interaction with Na(+)-K(+)-ATPase

J. J. Monroe and A. H. Tashjian Jr
Department of Molecular and Cellular Toxicology, Harvard School of Public Health, Boston, Massachusetts, USA.

Palytoxin (PTx) at nanomolar concentrations enhances the permeability of mammalian cell membranes to both Na+ and Ca2+. In basal human osteoblast-like Saos-2 cells, PTx (8 nM) caused a persistent decrease in cytosolic pH (pHi) of about 0.2 units, which required the presence of extracellular Ca2+ (Cae2+) and Na+ (Nae+). We acidified Saos-2 cells by incubation with nigericin to examine the action of PTx in cells with an activated Na+/H+ antiporter. Under these conditions, PTx increased the pHi without requiring Cae2+ or Nae+, and the alkalinization was unaffected by hexamethylene amiloride. We conclude that the PTx-induced rise in pHi did not involve the Na+/H+ antiporter. PTx increased the rate of 86Rb+ efflux. We propose that PTx induced alkalinization in nigericin-acidified cells by collapsing the K+ gradient. Exposure to ouabain had no effect on pHi, but it prevented the actions of PTx on PHi in both basal and nigericin-acidified cells. Ouabain-resistant mutant cells were less sensitive to PTx in extruding 86Rb+ than their ouabain-sensitive parents. We conclude that PTx interacts with the Na(+)-K(+)-adenosinetriphosphatase to regulate pHi in both basal and nigericin-acidified Saos-2 cells.


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