RESUMO
In the present paper, the modulation of the basolateral membrane (BLM) Na+ -ATPase activity of inner cortex from pig kidney by angiotensin II (Ang II) and angiotensin-(1-7) (Ang-(1-7)) was evaluated. Ang II and Ang-(1-7) inhibit the Na+ -ATPase activity in a dose-dependent manner (from 10(-11) to 10(-5) M), with maximal effect obtained at 10(-7) M for both peptides. Pharmacological evidences demonstrate that the inhibitory effects of Ang II and Ang-(1-7) are mediated by AT2 receptor: The effect of both polypeptides is completely reversed by 10(-8) M PD 123319, a selective AT2 receptor antagonist, but is not affected by either (10(-12) - 10(-5) M) losartan or (10(-10)-10(-7) M) A779, selective antagonists for AT1 and AT(1-7) receptors, respectively. The following results suggest that a PTX-insensitive, cholera toxin (CTX)-sensitive G protein/adenosine 3',5'-cyclic monophosphate (cAMP)/PKA pathway is involved in this process: (1) the inhibitory effect of both peptides is completely reversed by 10(-9) M guanosine 5'-O-(2-thiodiphosphate) (GDPbetaS; an inhibitor of the G protein activity), and mimicked by 10(-10) M guanosine 5'-O-(3-thiotriphosphate) (GTPgammaS; an activator of the G protein activity); (2) the effects of both peptides are mimicked by CTX but are not affected by PTX; (3) Western blot analysis reveals the presence of the Gs protein in the isolated basolateral membrane fraction; (4) (10(-10)-10(-6) M) cAMP has a similar and non-additive effect to Ang II and Ang-(1-7); (5) PKA inhibitory peptide abolishes the effects of Ang II and Ang-(1-7); and (6) both angiotensins stimulate PKA activity.