Renal AT Receptors Mediate Natriuresis via Protein Phosphatase PP2A.

BACKGROUND

How signals from activated angiotensin type-2 receptors (ATR) mediate inhibition of sodium ion (Na) reabsorption in renal proximal tubule cells is currently unknown. Protein phosphatases including PP2A (protein phosphatase 2A) have been implicated in ATR signaling in tissues other than kidney. We investigated whether inhibition of protein phosphatase PP2A reduced ATR-mediated natriuresis and evaluated changes in PP2A activity and localization after renal ATR activation in normal 4- and 10-week-old control Wistar-Kyoto rats and 4-week-old prehypertensive and 10-week-old hypertensive spontaneously hypertensive rats.

METHODS AND RESULTS

In Wistar-Kyoto rats, direct renal interstitial administration of selective ATR nonpeptide agonist Compound-21 (C-21) increased renal interstitial cyclic GMP (cGMP) levels, urine Na excretion, and simultaneously increased PP2A activity ≈2-fold in homogenates of renal cortical tubules. The cyclic GMP and natriuretic responses were abolished by concurrent renal interstitial administration of protein phosphatase inhibitor calyculin A. In renal proximal tubule cells in response to C-21, PP2A subunits A, B55α and C, but not B56γ, were recruited to apical plasma membranes together with ATRs. Calyculin A treatment abolished C-21-induced translocation of both ATR and PP2A regulatory subunit B55α to apical plasma membranes. Immunoprecipitation of ATR solubilized from renal cortical homogenates demonstrated physical association of ATR with PP2A A, B55α, and C but not B56γ subunits. In contrast, in spontaneously hypertensive rats, administration of C-21 did not alter urine Na excretion or PP2A activity and failed to translocate ATRs and PP2A subunits to apical plasma membranes.

CONCLUSIONS

In renal proximal tubule cells of Wistar-Kyoto rats, PP2A is activated and PP2A subunits AB55αC are recruited to C-21-activated ATRs during induction of natriuresis. This response is defective in prehypertensive and hypertensive spontaneously hypertensive rats, presenting a potential novel therapeutic target for treating renal Na retention and hypertension.