Kidney dopamine D1-like receptors and angiotensin 1-7 interaction inhibits renal Na+ transporters

Abstract

The role of dopamine D₁-like receptors (DR) in the regulation of renal Na⁺ transporters, natriuresis, and blood pressure is well established. However, the involvement of the angiotensin 1-7 (ANG 1-7)-Mas receptor in the regulation of Na⁺ balance and blood pressure is not clear. The present study aimed to investigate the hypothesis that ANG 1-7 can regulate Na⁺ homeostasis by modulating the renal dopamine system. Sprague-Dawley rats were infused with saline alone (vehicle) or saline with ANG 1-7, ANG 1-7 antagonist A-779, DR agonist SKF38393, and antagonist SCH23390. Infusion of ANG 1-7 caused significant natriuresis and diuresis compared with saline alone. Both natriuresis and diuresis were blocked by A-779 and SCH23390. SKF38393 caused a significant, SCH23390-sensitive natriuresis and diuresis, and A-779 had no effect on the SKF38393 response. Concomitant infusion of ANG 1-7 and SKF38393 did not show a cumulative effect compared with either agonist alone. Treatment of renal proximal tubules with ANG 1-7 or SKF38393 caused a significant decrease in Na⁺-K⁺-ATPase and Na⁺/H⁺ exchanger isoform 3 activity. While SCH23390 blocked both ANG 1-7- and SKF38393-induced inhibition, the DR response was not sensitive to A-779. Additionally, ANG 1-7 activated PKG, enhanced tyrosine hydroxylase activity via Ser⁴⁰ phosphorylation, and increased renal dopamine production. These data suggest that ANG 1-7, via PKG, enhances tyrosine hydroxylase activity, which increases renal dopamine production and activation of DR and subsequent natriuresis. This study provides evidence for a unidirectional functional interaction between two G protein-coupled receptors to regulate renal Na⁺ transporters and induce natriuresis.

Keywords: Na+-K+-ATPase; Na+/H+ exchanger; natriuresis; renal tubules.

Fig. 1.

Effect of angiotensin 1−7 (ANG 1–7) on urine flow (UF), urinary Na⁺ excretion (UNa), fractional excretion of Na⁺ (FE_Na), and glomerular filtration rate (GFR). Rats were infused with saline, and urine was collected for 45 min to establish a baseline. One group was continued on saline, whereas the other group was administered ANG 1–7 in saline for 45 min. UF (A), UNa (B), FE_Na (C), and GFR (D) were measured as described in materials and methods. n = 10–12 rats. *P < 0.05 vs. saline by repeated-measures ANOVA followed by a post hoc Newman-Keuls test.

Fig. 2.

Effect of angiotensin 1−7 (ANG 1–7) and dopamine D₁-like receptor (DR) agonist SKF38393 on urine flow (UF), urinary Na⁺ excretion (UNa), and fractional excretion of Na⁺ (FE_Na). Rats were infused with saline alone or saline with ANG 1–7, SKF38393, ANG 1–7 antagonist A-779, and DR blocker SCH23390. After drug infusion was initiated, urine was collected for 45 min to measure UF (A), UNa (B), and FE_Na (C). n = 10–12 rats. *P < 0.05 vs. saline by one-way ANOVA followed by post hoc Newman-Keuls test.

Fig. 3.

Effect of angiotensin 1−7 (ANG 1–7) and dopamine D₁-like receptor (DR) agonist SKF38393 on renal proximal tubular Na⁺ transporters Na⁺-K⁺-ATPase and Na⁺/H⁺ exchanger isoform 3 (NHE3). Proximal tubules were incubated with ANG 1–7 and SKF38393 in the presence and absence of ANG 1–7 antagonist A-779 and DR blocker SCH23390. Na⁺-K⁺-ATPase activity was measured directly in lysed tubules (A), whereas NHE3 activity was measured in brush-border membranes isolated after incubation of tubules with the desired drugs (B). n = 6–8 rats. *P < 0.05 vs. saline by one-way ANOVA followed by a post hoc Newman-Keuls test. Na⁺-K⁺-ATPase and NHE3 were assayed in quadruplicate from each rat.

Fig. 4.

Effect of angiotensin 1−7 (ANG 1–7) on PKG and tyrosine hydroxylase (TH) expression and activity. Renal proximal tubules were incubated with ANG 1–7 in the presence and absence of ANG 1–7 antagonist A-779, DR blocker SCH23390, PKG inhibitor KT5823, and TH inhibitor 3-iodo-l-tyrosine. Renal proximal tubular PKG activity (A) and PKA activity (B) are shown. TH expression and phosphorylation were determined by Western blot analysis (C) and ELISA (D). TH activity was determined by HPLC-MS (E). n = 6–8 rats. *P < 0.05 vs. saline by one-way ANOVA followed by a post hoc Newman-Keuls test. PKG and TH activity were assayed in quadruplicate from each rat; expression and Ser⁴⁰ phosphorylation (ELISA) were performed in quintuplicate from each rat.

Fig. 5.

Role of dopamine synthesis enzymes on angiotensin 1−7 (ANG 1–7)-induced inhibition of Na⁺ transporters Na⁺-K⁺-ATPase and Na⁺/H⁺ exchanger isoform 3 (NHE3). Proximal tubules were incubated with ANG 1–7 and SKF38393 in the presence and absence of PKG inhibitor KT5823, tyrosine hydroxylase inhibitor 3-iodo-l-tyrosine, and aromatic l-amino acid decarboxylase inhibitor 3-hydroxybenzylhydrazine dihydrochloride (HBH). Na⁺-K⁺-ATPase activity was measured directly in lysed tubules (A and B), whereas NHE3 activity was measured in brush-border membranes isolated after incubation of tubules with the desired drugs (C). n = 6–8 rats. *P < 0.05 vs. saline by one-way ANOVA followed by a post hoc Newman-Keuls test. Na⁺-K⁺-ATPase and NHE3 were assayed in quadruplicate from each rat.