Protein Carbonylation of an Amino Acid Residue of the Na/K‐ATPase α1 Subunit Determines Na/K‐ATPase Signaling and Sodium Transport in Renal Proximal Tubular Cells

Background We have demonstrated that cardiotonic steroids, such as ouabain, signaling through the Na/K‐ ATP ase, regulate sodium reabsorption in the renal proximal tubule. By direct carbonylation modification of the Pro222 residue in the actuator (A) domain of pig Na/K‐ ATP ase α1 subunit, reactive oxygen species are required for ouabain‐stimulated Na/K‐ ATP ase/c‐Src signaling and subsequent regulation of active transepithelial 22 Na + transport. In the present study we sought to determine the functional role of Pro222 carbonylation in Na/K‐ ATP ase signaling and sodium handling. Methods and Results Stable pig α1 knockdown LLC ‐ PK 1‐originated PY ‐17 cells were rescued by expressing wild‐type rat α1 and rat α1 with a single mutation of Pro224 (corresponding to pig Pro222) to Ala. This mutation does not affect ouabain‐induced inhibition of Na/K‐ ATP ase activity, but abolishes the effects of ouabain on Na/K‐ ATP ase/c‐Src signaling, protein carbonylation, Na/K‐ ATP ase endocytosis, and active transepithelial 22 Na + transport. Conclusions Direct carbonylation modification of Pro224 in the rat α1 subunit determines ouabain‐mediated Na/K‐ ATP ase signal transduction and subsequent regulation of renal proximal tubule sodium transport.