H+-ATP ase activity on unilateral ureteral obstruction: interaction of endogenous nitric oxide and angiotensin II

PATRICIA GARRAMUÑO VALLÉS; WALTER MANUCHA

KIDNEY INTERNATIONAL

Nature Publishing Group

Lugar: New York, Springer-Verlag.; Año: 2000 vol. 58 p. 1641 - 1651

0085-2538

Background. A number of cytokines, vasoactive compounds, chemoattractant molecules, and growth factors are up-regu­lated in obstruction. Following the onset of ureteral obstruc­tion, angiotensin II production is rapidly stimulated. Cytokine­ induced expression of inducible nitric oxide synthase (iNOS) has been reported in primary cultures of inner medulIary col­lecting duct (IMCD) cells. We found that the defective urinary acidification in unilateral ureteral obstruction (UUO) includes an intensive decrease in bafilomycin-sensitive H+ -ATPase ac­tivity in microdissected IMCD segments. Melhods. To investigate the interaction between endogenous nitric oxide and angiotensin II on H+-ATPase activity, we used microdissected IMCD segments of unilateralIy obstructed, con­tralateral and control kidneys to measure  bafilomycin­ sensitive ATPase activity and nitric oxide synthase (NOS) activity. The generated NO was also evaluated. Resulls. Preincubation of obstructed IMCD segments in the presence of a competitive inhibitor of NOS, NG-nitro-L-arginine methyl ester (L-NAME) 1 mmoL, and in the presence of a spe­cific inhibitor of calcium/calmodulin-independent NOS (iNOS), .. aminoguanidine 1 mmoL, each for 60 minutes, significantly in­creased bafilomycin-sensitive H+ -ATPase. A greater increase on iNOS activity (fmol 3H] citrulline/min/µg protein) and a lesser increase in calcium/calmodulin-dependent NOS activity (cNOS) were observed in the obstructed renal medulla. This inhibitory effect of obstruction was abolished when IMCDs were incubated with 10-5 to 10-8 mol losartan. Decreasing doses of the angiotensin II type 1 (ATI) receptor inhibitor caused an increase in bafilomycin-sensitive H+ -ATPase, with a maxi­mum increase at 10-8 mol losartan. A decrease on iNOS activ­ity was demonstrated in the obstructed renal medulla incubated with losartan in concentrations of 10-5 to 10-8 mol, the same losartan concentrations that showed recovery of vacuolar­H+-ATPase activity. Similarly, a decrease on the generation of NO after incubation with losartan 10-5 to 10-8 mol was shown. .Conclusion. From these results, we suggest that endogenous NO increased by iNOS is involved in the inhibition of H+-ATPase activity in obstructed IMCD segments.­ The recovery of H+ATPase activity in IMCD of obstructed kidneys induced by losartan may be related to a decrease of inducible NOS activity.