Characterization of acute inhibition of Na/H exchanger NHE-3 by dopamine in opossum kidney cells

Characterization of acute inhibition of Na/H exchanger NHE-3 by dopamine in opossum kidney cells. Background Dopamine (DA) is a principal natriuretic hormone that defends extracellular fluid volume from a Na load. Natriuresis is effected partly through inhibiting the proximal tubule Na/H exchanger NHE-3. Changes in NHE-3 phosphorylation is one mechanism by which NHE-3 activity is regulated. Methods We used opossum kidney (OK) cells to characterize the differential and synergistic effects of DA receptor subtype-1 (DA 1 ) and -2 (DA 2 ) agonists and the effect of blockade of protein kinase A (PKA) or protein kinase C (PKC) on NHE-3 activity and phosphorylation. Results DA and DA 1 agonists inhibited NHE-3 activity, and DA 1 antagonist blocked the effect of either DA or DA 1 agonist. DA 2 agonist alone had no effect, but DA 2 antagonist reduced the DA effect on NHE-3 activity. DA 1 and DA 2 agonists together were more potent than DA 1 alone. PKA inhibition eliminated the effect of DA 1 agonist and partially blocked the effect of DA on NHE-3 activity. PKC inhibition did not block the DA effect. DA 1 agonist and PKA activation phosphorylated NHE-3 on identical sites. Despite lack of effect on NHE-3 activity, DA 2 agonists increased NHE-3 phosphorylation. DA-induced NHE-3 phosphorylation was distinct from DA 1 and PKA but closely resembled DA 2 . Conclusion We postulate the following: ( 1 ) DA modifies NHE-3 phosphorylation by activating PKA through DA 1 and by other kinases/phosphatases via DA 2 . ( 2 ) DA 1 is sufficient to inhibit NHE-3, while DA 2 is insufficient but plays a synergistic role by altering NHE-3 phosphorylation.