Receptor-mediated inhibition of renal Na+-K+-ATPase is associated with endocytosis of its alpha - and beta -subunits

The mechanisms involved in receptor-mediated inhibition ofNa⁺-K⁺-ATPaseremain poorly understood. In this study, we evaluate whether inhibitionof proximal tubuleNa⁺-K⁺-ATPaseactivity by dopamine is linked to its removal from the plasma membraneand internalization into defined intracellular compartments.Clathrin-coated vesicles were isolated by sucrose gradientcentrifugation and negative lectin selection, and early and lateendosomes were separated on a flotation gradient. Inhibition ofNa⁺-K⁺-ATPaseactivity by dopamine, in contrast to its inhibition by ouabain, wasaccompanied by a sequential increase in the abundance of the-subunit in clathrin-coated vesicles (1 min), early endosomes (2.5 min), and late endosomes (5 min), suggesting its stepwise translocationbetween these organelles. A similar pattern was found for the-subunit. The increased incorporation of both subunits in allcompartments was blocked by calphostin C. The results demonstrate thatthe dopamine-induced decrease inNa⁺-K⁺-ATPaseactivity in proximal tubules is associated with internalization of its- and -subunits into early and late endosomes via aclathrin-dependent pathway and that this process is protein kinase Cdependent. The presence ofNa⁺-K⁺-ATPasesubunits in endosomes suggests that these compartments may constitutenormal traffic reservoirs during pump degradation and/orsynthesis.