Background:
How signals from activated angiotensin type-2 receptors (AT
2
R) mediate inhibition of sodium ion (Na+) reabsorption in renal proximal tubule cells (RPTCs) is currently unknown. Protein phosphatases including protein phosphatase 2A (PP2A) have been implicated in AT2R signaling in tissues other than kidney. We investigated whether inhibition of protein phosphatase PP2A reduced AT
2
R-mediated natriuresis and evaluated changes in PP2A activity and localization after renal AT
2
R activation in normal 4- and 10-week-old control Wistar-Kyoto rats (WKY) and 4-week-old pre-hypertensive and 10-week-old hypertensive spontaneously hypertensive rats (SHR).
Methods and Results:
In WKY, direct renal interstitial (RI) administration of selective AT
2
R non-peptide agonist Compound-21 (C-21) increased RI cyclic GMP (cGMP) levels, urine Na
+
excretion (U
Na
V), and simultaneously increased PP2A activity ≅ 2-fold in homogenates of renal cortical tubules. The cGMP and natriuretic responses were abolished by concurrent RI administration of protein phosphatase inhibitor calyculin A (CAL). In RPTCs in response to C-21, PP2A subunits A, B55α and C, but not B56γ, were recruited to apical plasma membranes together with AT
2
Rs. CAL treatment abolished C-21-induced translocation of both AT
2
R and PP2A regulatory subunit B55α to apical plasma membranes. Immunoprecipitation of AT
2
R solubilized from renal cortical homogenates demonstrated physical association of AT
2
R with PP2A A, B55α, and C but not B56γ subunits. In contrast, in SHR, administration of C-21 did not alter UNaV or PP2A activity and failed to translocate AT
2
Rs and PP2A subunits to apical plasma membranes.
Conclusions:
In RPTCs of WKY, PP2A is activated and PP2A subunits AB55αC are recruited to C-21-activated AT
2
Rs during induction of natriuresis. This response is defective in pre-hypertensive and hypertensive SHR, presenting a potential novel therapeutic target for treating renal Na+ retention and hypertension.