Peroxynitrite and the regulation of Na+,K+-ATPase activity by angiotensin II in the rat proximal tubule

NO reacts spontaneously with superoxide to produce the potent oxidant peroxynitrite. Studies were designed to examine the role of NO-derived oxidants and peroxynitrite on the regulation of Na+,K+-ATPase activity by angiotensin 11 (ANG II) freshly isolated rat proximal tubules. At picomolar concentrations ANG 11 stimulates Na+,K+-ATPase activity, but at nanomolar concentrations stimulation is lost. Superoxide dismutase (SOD) was used to examine the role of superoxide and deferoxamine (DFO) and uric acid (UA) were used to examine the role of peroxynitrite. SOD (200 U/mL, 5-min preincubation) restored the stimulatory effect of ANG 11 (1.31 +/- 0.08-fold; n = 4; P < 0.05 compared to 10(-7) M alone), suggesting a role for superoxide. DFO (100 mum, 5-min preincubation) also restored the stimulatory effect of ANG 11 (1.40 +/- 0.08-fold; n = 4; P < 0.05, compared to 10(-7) M alone), as did UA (1.22 +/- 0.07-fold; n = 5; P < 0.05, compared to 10(-7) M alone). The NO synthesis inhibitor, N-monomethyl-L-arginine (L-NMMA, 2 mM; 5-min preincubation), also unmasked a stimulatory effect of ANG 11 at 10(-7) M (1.4 +/- 0.1-fold; n = 7; P < 0.05, compared to 10(-7) M alone). The generation of peroxynitrite was further evidenced by the formation of 3-nitrotyrosine (3-NT). 3-NT increased 3.5-fold in tubules exposed to ANG 11 (10(-7) M) (0.0054 +/- 0.0019 3-NT/100 tyrosines for control and 0.019 +/- 0.0058 3-NT/100 tyrosines for ANG 11, P < 0.05; n = 4) and L-NMMA prevented the increase. These data suggest that peroxynitrite signaling participates in the regulation of renal of Na+,K+-ATPase activity. (C) 2002 Elsevier Science (USA). All rights reserved.