title: Enhancement in cellular Na+K+ATPase activity by low doses of peroxynitrite in mouse renal tissue and in cultured HK2 cells.
abstract: In the normal condition, endogenous formation of peroxynitrite (ONOO-) from the interaction of nitric oxide and superoxide has been suggested to play a renoprotective role. However, the exact mechanism associated with renoprotection by this radical compound is not yet clearly defined. AlthoughONOO- usually inhibits renal tubular Na(+)K(+)ATPase (NKA) activity at high concentrations (micromolar to millimolar range [μM-mM], achieved in pathophysiological conditions), the effects at lower concentrations (nanomolar range [nM], relevant in normal condition) remain unknown. To examine the direct effect ofONOO- onNKAactivity, preparations of cellular membrane fraction from mouse renal tissue and from culturedHK2 cells (human proximal tubular epithelial cell lines) were incubated for 10 and 30 min each with different concentrations ofONOO- (10 nmol/L-200 μmol/L).NKAactivity in these samples (n = 5 in each case) was measured via a colorimetric assay capable of detecting inorganic phosphate. At high concentrations (1-200 μmol/L),ONOO- caused dose-dependent inhibition ofNKAactivity (-3.0 ± 0.6% and -36.4 ± 1.4%). However,NKAactivity remained unchanged at 100 and 500 nmol/LONOO- concentration, but interestingly, at lower concentrations (10 and 50 nmol/L),ONOO- caused small but significant increases in theNKAactivity (3.3 ± 1.1% and 3.1 ± 0.6%). Pretreatment with aONOO- scavenger, mercaptoethylguanidine (MEG; 200 μmol/L), prevented these biphasic responses toONOO-. This dose-dependent biphasic action ofONOO(-)onNKAactivity may implicate that this radical compound helps to maintain sodium homeostasis either by enhancing tubular sodium reabsorption under normal conditions or by inhibiting it during oxidative stress conditions.
authors.affiliation: Department of Physiology, Hypertension and Renal Center of Excellence, Tulane University Health Sciences Center, New Orleans, Louisiana.
authors.forename: Arpan K
authors.initials: AK
authors.lastname: Maiti
authors.affiliation: Department of Physiology, Hypertension and Renal Center of Excellence, Tulane University Health Sciences Center, New Orleans, Louisiana.
authors.forename: Mohammed T
authors.initials: MT
authors.lastname: Islam
authors.affiliation: Department of Physiology, Hypertension and Renal Center of Excellence, Tulane University Health Sciences Center, New Orleans, Louisiana.
authors.forename: Ryousuke
authors.initials: R
authors.lastname: Satou
authors.affiliation: Department of Physiology, Hypertension and Renal Center of Excellence, Tulane University Health Sciences Center, New Orleans, Louisiana majid@tulane.edu.
authors.forename: Dewan S A
authors.initials: DS
authors.lastname: Majid
mesh_terms: D000818:Animals; D002460:Cell Line; D002462:Cell Membrane / Q000187:drug effects* / Q000201:enzymology; D004305:Dose-Response Relationship, Drug; D020536:Enzyme Activators / Q000494:pharmacology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004847:Epithelial Cells / Q000187:drug effects* / Q000201:enzymology; D016166:Free Radical Scavengers / Q000494:pharmacology; D006801:Humans; D007687:Kidney Tubules, Proximal / Q000187:drug effects* / Q000201:enzymology; D008810:Mice, Inbred C57BL; D009569:Nitric Oxide / Q000378:metabolism; D030421:Peroxynitrous Acid / Q000494:pharmacology*; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D013997:Time Factors
chemical_list: D020536:Enzyme Activators; D004791:Enzyme Inhibitors; D016166:Free Radical Scavengers; D030421:Peroxynitrous Acid; D009569:Nitric Oxide; D000254:Sodium-Potassium-Exchanging ATPase
keywords: HK2 cells; Peroxynitrite; cellular Na+K+ATPase activity; nitric oxide; superoxide