Adenosine reverses the stimulatory effect of angiotensin II on the renal Na+-ATPase activity through the A2 receptor

In the present paper, we report the modulation of the Angiotensin II (Ang II)-stimulated Na+-ATPase activity of the proximal tubule basolateral membrane by adenosine (Ado). Preincubation of isolated basolateral membrane with 10-8M Ang II increases the Na+-ATPase activity from 7.5±0.3 (control) to 14.6±0.9 nmol Pi×mg-1×min-1nmol Pi×mg-1×min-1 (p<0.05). Incubation of Ang II-stimulated enzyme with 10-6M Ado, in the presence of the A1 receptor antagonist DPCPX (10-6M), completely reverses the Ang II-induced effect bringing the Na+-ATPase activity to the basal level. The following evidences demonstrate involvement of the A2 receptor/Gs protein/adenylyl cyclase/PKA signaling pathway in the inhibitory effect induced by Ado on the Ang II-stimulated Na+-ATPase activity in the presence of the DPCPX: 1) the inhibitory effect of Ado is abolished by the A2 receptor selective antagonist DMPX (10−8M); 2) the effect induced by Ado is blocked by 10-8M GDPβS and mimicked by 10-9M cholera toxin and 10-8M GTPγS; 3) the stimulatory effect of Ang II is reduced by 10-6M forskolin, an activator of adenylyl cyclase, or 10-6M cAMP; 4) Ado stimulates PKA activity; 5) the inhibitory effect induced by this nucleoside is reversed by the PKA inhibitor peptide.