Angiotensin II activates the ouabain-insensitive Na+-ATPase from renal proximal tubules through a G-protein

Angiotensin II (AG II) stimulates the ouabain-insensitive, furosemide- sensitive Na+-ATPase present in the basolateral membrane of pig renal proximal tubules in a dose dependent manner. Maximum effect was obtained with 10(-8) M AG II, which corresponded to an activity 134% higher than control. Half of the maximum effect was observed between 10(-11) M and 10(-10) M, corresponding to physiological hormone levels. Saralasin, an AG II peptide analogue receptor antagonist, abolished the phenomenon, demonstrating that AG II interacts with specific sites in pig proximal tubules. The AG II stimulatory effect was also prevented by dithiothreitol (DTT), a reducing compound, and by 10 nM losartan, a non-peptide antagonist highly specific for AT(1) receptors, characterizing AG II binding to ATI receptors. GTP gamma S, a non-hydrolysable GTP analogue, increased by 159% the enzyme activity as compared to the control values. The simultaneous addition of 10(-5) M GTP gamma S and 10(-8) M AG II did not have additive effects. Furthermore, the stimulatory action of AG II was completely abolished by 0.1 mu M GDP beta S, a non-hydrolysable GDP analogue. Two mu g ml(-1) pertussis toxin, an inhibitor of G(i)-protein, did not modulate the AG II stimulatory effect. On the other hand, the Na+-ATPase activity was enhanced 100% in the presence of cholera toxin and 85% in the presence of both AG II and cholera toxin. Taken together, these data suggest that AG II activates the Na+-ATPase activity through AT1 receptors coupled to a pertussis-insensitive and cholera-sensitive G-protein. (C) 1999 Elsevier Science B.V. All rights reserved.