Involvement of the Gi/o/cGMP/PKG pathway in the AT2-mediated inhibition of outer cortex proximal tubule Na+-ATPase by Ang-(1-7)

The molecular mechanisms involved in the Ang-(1-7) [angiotensin-( 1-7)] effect on sodium renal excretion remain to be determined. In a previous study, we showed that Ang-(1-7) has a biphasic effect on the proximal tubule Na+-ATPase activity, with the stimulatory effect mediated by the AT(1) receptor. In the present study, we investigated the molecular mechanisms involved in the inhibition of the Na+-ATPase by Ang-(1-7). All experiments were carried out in the presence of 0.1 nM losartan to block the AT(1) receptor-mediated stimulation. In this condition, Ang-(1-7) at 0.1 nM inhibited the Na+-ATPase activity of the proximal tubule by 54 %. This effect was reversed by 10 nM PD 123319, a specific antagonist of the AT(2) receptor, and by 1 mu M GDP[beta-S] (guanosine 5'-[beta-thio]diphosphate), an inhibitor of G protein. Ang-(1-7) at 0.1 M induced [S-35]GTP[S] (guanosine 5'-[gamma-[S-35]thio]triphosphate) binding and 1 mu g/ml pertussis toxin, an inhibitor of G(i/o) protein, reversed the Ang-(1-7) effect. Furthermore, it was observed that the inhibitory effect of Ang-(1-7) on the Na+-ATPase activity was completely reversed by 0.1 mu M LY83583, an inhibitor of guanylate cyclase, and by 2 mu M KT5823, a PKG (protein kinase G) inhibitor, and was mimicked by 10 nM d-cGMP (dibutyryl cGMP). Ang-(1-7) increased the PKG activity by 152 % and this effect was abolished by 10 nM PD123319 and 0.1 mu M LY83583. Taken together, these data indicate that Ang-(1-7) inhibits the proximal tubule Na+-ATPase by interaction with the AT(2) receptor that subsequently activates the G(i/o) protein/cGMP/PKG pathway.