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- sens itive 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, corresp onding to physiological hormone levels. Saralasin, an AG II peptide analogu e receptor antagonist, abolished the phenomenon, demonstrating that AG II i nteracts with specific sites in pig proximal tubules. The AG II stimulatory effect was also prevented by dithiothreitol (DTT), a reducing compound, an d by 10 nM losartan, a non-peptide antagonist highly specific for AT(1) rec eptors, characterizing AG II binding to ATI receptors. GTP gamma S, a non-h ydrolysable GTP analogue, increased by 159% the enzyme activity as compared to the control values. The simultaneous addition of 10(-5) M GTP gamma S a nd 10(-8) M AG II did not have additive effects. Furthermore, the stimulato ry action of AG II was completely abolished by 0.1 mu M GDP beta S, a non-h ydrolysable 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 h and, the Na+-ATPase activity was enhanced 100% in the presence of cholera t oxin and 85% in the presence of both AG II and cholera toxin. Taken togethe r, these data suggest that AG II activates the Na+-ATPase activity through AT1 receptors coupled to a pertussis-insensitive and cholera-sensitive G-pr otein. (C) 1999 Elsevier Science B.V. All rights reserved.