Enhancement of cellular Na+K+ATPase activity in the mouse renal tissue in‐vitro with low concentration of peroxynitrite

Endogenous production of peroxynitrite (ONOO° − ) in normal condition has been suggested to play a renoprotective role. However, the exact mechanism associated with this protection is not yet clearly defined. ONOO° − at higher concentrations (μM to mM; in pathology) can inhibit cellular Na + K + ATPase (NKA) activity. However, the effect of ONOO° − on NKA activity at low conc. (nM; which is physiologically more relevant) remains unknown. To examine the hypothesis that ONOO° − at low conc. enhances NKA activity, preparations of cellular membrane fraction from mouse renal tissue (n=5 in each case) were incubated for 10 min each with different conc. of ONOO° − (10 nM to 200 μM). NKA activity in these samples was measured via a colorimetric assay capable of detecting inorganic phosphate. At high conc. (1–200 μM), ONOO° − caused dose‐dependent inhibition of NKA activity (−3.0±0.6 % to – 36.4±1.4 %) as reported previously. However, NKA activity remained unchanged at 100 and 500 nM ONOO° − conc., but interestingly, at lower conc.(10 and 50 nM), ONOO° − caused a small but significant increases in the NKA activity (3.3±1.1 % & 3.1±0.6 %). These responses were prevented at preparations co‐incubated with ONOO° − scavenger, mercapto ethyl guanadine (200 μM). These data indicate that NKA activity remains unaffected or rather increased at the physiological conc. of ONOO° − that facilitates the reno‐protective role for this oxidant molecule.