Activation of D2-like receptors causes recruitment of tyrosine-phosphorylated NKA alpha 1-subunits in kidney.

The present study investigates the cellular mechanisms responsible for dopamine D2-like receptor-mediated stimulation of Na+ - K+-ATPase in the proximal tubules of the kidney. Previously, we showed that D2-like receptor-mediated increase in Na+ - K+-ATPase involves an increase in the maximum rate of Na+ - K+-ATPase activity (V(max)). Therefore, we tested the hypothesis that D2-like receptor-mediated stimulation of Na+ - K+-ATPase requires phosphorylation and recruitment of alpha 1-subunits of the enzyme from cytosol to the membrane. This hypothesis was tested by Western blotting for Na+ - K+-ATPase alpha 1-subunits in proximal tubular membrane. Treatment of the proximal tubules with bromocriptine (D2-like receptor agonist) caused an increase in Na+ - K+-ATPase alpha 1-subunit abundance in the membrane preparations. This effect was blocked by genistein (tyrosine kinase inhibitor), suggesting a role for tyrosine phosphorylation. Moreover, bromocriptine caused an increase in tyrosine phosphorylation of membrane-bound Na+ - K+-ATPase alpha 1-subunits. This effect was blocked by bafilomycin A1 (vesicular trafficking inhibitor), which suggested that this increase was due to the recruitment of tyrosine-phosphorylated Na+ - K+-ATPase alpha 1-subunits. In conclusion, we have demonstrated that activation of D2-like receptors increases Na+ - K+-ATPase activity by recruitment of the tyrosine-phosphorylated alpha 1-subunits in the proximal tubules of the kidney.