Synergism between Angiotensin receptors ligands: Role of Angiotensin‐(1‐7) in modulating AT(2)R agonist response on nitric oxide in kidney cells

Angiotensin‐(1‐7), an endogenous agonist for the MasR, has been shown to interact with ang‐II AT(1)R and AT(2)R. Earlier we showed a physical and functional interaction between MasR and AT(2)R in response to their respective agonists ang‐(1‐7) and C21. Moreover, ang‐(1‐7) is cardio‐protective via AT(1)R and alters ang‐II function. Such complex nature of ang‐(1‐7) function is not clearly understood, particularly in relation to its functional interaction with these receptors. We tested how ang‐(1‐7) affects AT(2)R function by utilizing HK‐2 cells. The HK‐2 cells were treated with a wide range of concentrations of angiotensin receptor agonists. The generation of NO(•) in response to agonists was determined as a readout and subjected to Bliss definition (δ score) to assess the nature of functional interaction between these receptors. Preincubation with ang‐(1‐7) followed by incubation with endogenous AT(1)R/AT(2)R agonist ang‐II (δ = 162) or selective AT(2)R agonist C21 (δ = 304) synergized NO(•) formation. The synergism was also observed when the order of incubation with ang‐(1‐7)/C21 was reversed (δ = 484), but not when the cells were simultaneously incubated with a mixture of ang‐(1‐7) and C21 (δ = 76). The synergism with nonpeptidic MasR agonist AVE0991 followed by C21 (δ = 45) was minimal. Ligand binding experiment suggested the binding of ang‐(1‐7) with these three receptors. However, the synergism observed with ang‐(1‐7) and ang‐II/C21 was sensitive to the antagonists of AT(2)R (PD123319) and AT(1)R (candesartan), but not MasR (A779). Ang‐(1‐7) at lower concentrations synergies the AT(2)R function in an AT(1)R‐dependent but MasR‐independent manner. This phenomenon may have a physiological significance.