Hormonal-dependent recruitment of Na+,K+-ATPase to the plasmalemma is mediated by PKCβ and modulated by [Na+]i

1 The present study demonstrates that stimulation of hormonal receptors of proximal tubule cells with the serotonin-agonist 8-hydroxy-2-(di-n-propylamino) tetraline (8-OH-DPAT) induces an augmentation of Na+,K+-ATPase activity that results from the recruitment of enzyme molecules to the plasmalemma. 2 Cells expressing the rodent wild-type Na+,K+-ATPase alpha-subunit had the same basal Na+,K+-ATPase activity as cells expressing the alpha-subunit S11A or S18A mutants, but stimulation of Na+,K+-ATPase activity was completely abolished in either mutant. 3 8-OH-DPAT treatment of OK cells led to PKCbeta-dependent phosphorylation of the alpha-subunit Ser-11 and Ser-18 residues, and determination of enzyme activity with the S11A and S18A mutants indicated that both residues are essential for the agonist-dependent stimulation of Na+,K+-ATPase activity. 4 When cells were treated with both dopamine and 8-OH-DPAT, an activation of Na+,K+-ATPase was observed at basal intracellular sodium concentration (similar to9 mm), and this activation was gradually reduced and became a significant inhibition as the concentration of intracellular sodium gradually increased from 9 to 19 mm. Thus, besides the antagonistic effects of dopamine and 8-OH-DPAT, intracellular sodium modulates whether an activation or an inhibition of Na+,K+-ATPase is produced.