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

Most vital cellular functions aredependent on a fine-tuned regulation of intracellular ion homeostasis.Here we have demonstrated, using COS cells that were untransfected ortransfected with wild-type rat ouabain-resistantNa⁺-K⁺-ATPase, that partial inhibition ofNa⁺-K⁺-ATPase has a dramatic influence oncell attachment to fibronectin. Ouabain dose-dependently decreasedattachment in untransfected cells and in cells expressing wild-typeNa⁺-K⁺-ATPase, but not in cells expressingouabain-insensitive Na⁺-K⁺-ATPase, whereasinhibition of Na⁺-K⁺-ATPase by loweringextracellular K⁺ concentration decreased attachment in allthree cell types. Thirty percent inhibition ofNa⁺-K⁺-ATPase significantly attenuatedattachment. Na⁺-K⁺-ATPase inhibition caused asustained increase in the intracellular Ca²⁺ concentrationthat obscured Ca²⁺ transients observed in untreated cellsduring attachment. Inhibitors of Ca²⁺ transporterssignificantly decreased attachment, but inhibition ofNa⁺/H⁺ exchanger did not. Ouabain reduced focaladhesion kinase autophosphorylation but had no effect on cell surfaceintegrin expression. These results suggest that the level ofNa⁺-K⁺-ATPase activity strongly influences cellattachment, possibly by an effect on intracellular Ca²⁺.