Role of phospholemman and the 70 kDa inhibitor protein in regulating Na/K ATPase activity in pulmonary artery smooth muscle cells under U46619 stimulation

Treatment of bovine pulmonary smooth muscle cells with U46619 inhibited the Na⁺/K⁺ ATPase activity in two parallel pathways: one of which is mediated via glutathionylation of the pump and the other by augmenting the inhibitory activity of the 70 kDa inhibitor protein of Na⁺/K⁺ ATPase. Although phospholemman deglutathionylates the pump leading to its activation, the inhibitor is responsible for irreversible inhibition of Na⁺/K⁺ ATPase in an isoform specific manner during treatment of the cells with U46619.