Dopamine Inhibits The Na+/H+ Exchanger Nhe3 Via Protein Phosphatase 2a

Nephrogenic dopamine is a potent natriuretic paracrine/autocrine hormone that is central for mammalian sodium homeostasis. In the renal proximal tubule, dopamine induces natriuresis partly by inhibiting the sodium/proton exchanger NHE3. The signaling pathways involved in this regulation are incompletely understood. We describe the role of the serine/threonine protein phosphatase 2A (PP2A) in the regulation of NHE3 by dopamine. The PP2A regulatory subunit B56 delta isoform directly associates with the carboxy‐terminal hydrophilic putative cytoplasmic domain of NHE3 (NHE3‐cyto), as demonstrated by yeast‐two‐hybrid, co‐immunoprecipitation, blot overlay and in vitro pull‐down assays. This interaction involves more than one region of NHE3‐cyto. NHE3‐cyto is a substrate for purified PP2A in an in vitro dephosphorylation reaction. In cultured renal cells, inhibition of PP2A by either okadaic acid or by overexpression of the simian virus 40 (SV40) small t antigen blocks the ability of dopamine to inhibit NHE3 activity and to reduce surface NHE3 protein. Dopamine‐induced NHE3 internalization is also blocked by okadaic acid ex vivo in rat kidney cortical slices. These studies demonstrate that PP2A is an integral and critical part of the signal transduction pathway between dopamine receptor activation and NHE3 inhibition.