Changes in Na+-K+-ATPase activity influence cell attachment to fibronectin

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Abstract
Most vital cellular functions are dependent on a fine-tuned regulation of intracellular ion homeostasis. Here we have demonstrated, using COS cells that were untransfected or transfected with wild-type rat ouabain-resistant Na+-K+-ATPase, that partial inhibition of Na+-K+-ATPase has a dramatic influence on cell attachment to fibronectin. Ouabain dose-dependently decreased attachment in untransfected cells and in cells expressing wild-type Na+-K+-ATPase, but not in cells expressing ouabain-insensitive Na+-K+-ATPase, whereas inhibition of Na+-K+-ATPase by lowering extracellular K+ concentration decreased attachment in all three cell types. Thirty percent inhibition of Na+-K+-ATPase significantly attenuated attachment. Na+-K+-ATPase inhibition caused a sustained increase in the intracellular Ca2+ concentration that obscured Ca2+ transients observed in untreated cells during attachment. Inhibitors of Ca2+ transporters significantly decreased attachment, but inhibition of Na+/H+ exchanger did not. Ouabain reduced focal adhesion kinase autophosphorylation but had no effect on cell surface integrin expression. These results suggest that the level of Na+-K+-ATPase activity strongly influences cell attachment, possibly by an effect on intracellular Ca2+.