Modulation of Na+/K+ exchange potentiates lipopolysaccharide-induced gene expression in murine peritoneal macrophages

The role of Na+/K+ exchange in regulating lipopolysaccharide (LPS)-mediated induction of cytokine gene expression has been examined in murine peritoneal macrophages. Depletion of K+ from the culture medium resulted in a three- to five-fold potentiation of tumor necrosis factor-alpha (TNF alpha), KC (gro), and IP-10 mRNA expression in LPS-treated macrophages. The potentiating effect was apparently the result of inhibition of Na+/K+ exchange through the Na+/K(+)-adenosine triphosphatase (ATPase) because ouabain-mediated inhibition of Na+/K(+)-ATPase was also able to potentiate cytokine mRNA expression as much or more than did K+ depletion. The effects of K+ depletion or ouabain treatment were not caused by depolarization of the macrophage membrane because depolarization mediated by elevating extracellular K+ levels was inhibitory to cytokine mRNA expression. Depletion of Na+ by substitution with choline in the culture medium also markedly potentiated LPS-induced gene expression. The Na+/H+ antiporter was not, however, involved in potentiating cytokine expression because treatment of macrophages with amiloride either had no effect on or was inhibitory to the LPS-induced changes in mRNA levels. The potentiation of gene expression was selective and was at least partially the result of increased transcriptional activity of each gene. Whereas Na+ depletion and ouabain both inhibited 86Rb+ uptake by macrophages, treatment with LPS had no effect either on Rb+ uptake or on efflux. Thus altered Na+/K+ exchange is not a component of the primary signalling pathway(s) mediating response to LPS. Nevertheless, modulation of macrophage Na+/K+ exchange by agents encountered during an inflammatory response may be an important determinant of the magnitude and quality of specific gene expression.