Synergism between Angiotensin receptors ligands: Role of Angiotensin-(1-7) in modulating AT 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 R and AT R. Earlier we showed a physical and functional interaction between MasR and AT R in response to their respective agonists ang-(1-7) and C21. Moreover, ang-(1-7) is cardio-protective via AT 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 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 R/AT R agonist ang-II (δ = 162) or selective AT 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 R (PD123319) and AT R (candesartan), but not MasR (A779). Ang-(1-7) at lower concentrations synergies the AT R function in an AT R-dependent but MasR-independent manner. This phenomenon may have a physiological significance.