Mechanism of depression in cardiac sarcolemmal Na+-K+-ATPase by hypochlorous acid.
Oxidative stress during pathological conditions such as ischemia-reperfusion is known to promote the formation of hypochlorous acid (HOCl) in the heart and to result in depression of cardiac sarcolemmal (SL) Na+-K+-ATPase activity. In this study, we examined the direct effects of HOCl on SL Na+-K+-ATPase from porcine heart. HOCl decreased SL Na+-K+-ATPase activity in a concentration- and time-dependent manner. Characterization of Na+-K+-ATPase activity in the presence of different concentrations of MgATP revealed a decrease in the maximal velocity (Vmax) value, without a change in affinity for MgATP on treatment of SL membranes with 0.1 mM HOCl. The Vmax value of Na+-K+-ATPase, when determined in the presence of different concentrations of Na+, was also decreased, but affinity for Na+ was increased when treated with HOCl. Formation of acylphosphate by SL Na+-K+-ATPase was not affected by HOCl. Scatchard plot analysis of [3H]ouabain binding data indicated no significant change in the affinity or maximum binding capacity value for ouabain binding following treatment of SL membranes with HOCl. Western blot analysis of Na+-K+-ATPase subunits in HOCl-treated SL membranes showed a decrease (34 +/- 9% of control) in the beta1-subunit without any change in the alpha1- or alpha2-subunits. These data suggest that the HOCl-induced decrease in SL Na+-K+-ATPase activity may be due to a depression in the beta1-subunit of the enzyme.
Kato
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Institute of Cardiovascular Sciences, St. Boniface General Hospital Research Centre, and Department of Physiology, Faculty of Medicine, University of Manitoba, Winnipeg, Manitoba, Canada R2H 2A6.
Shao
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Elimban
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Lukas
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Dhalla
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D000255:Adenosine Triphosphate / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D001665:Binding Sites; D004229:Dithiothreitol / Q000494:pharmacology; D006997:Hypochlorous Acid / Q000494:pharmacology*; D007700:Kinetics; D008715:Methionine / Q000494:pharmacology; D009206:Myocardium / Q000201:enzymology*; D010042:Ouabain / Q000378:metabolism; D012508:Sarcolemma / Q000201:enzymology*; D000254:Sodium-Potassium-Exchanging ATPase / Q000187:drug effects / Q000378:metabolism*; D013552:Swine
D010042:Ouabain; D006997:Hypochlorous Acid; D000255:Adenosine Triphosphate; D008715:Methionine; D000254:Sodium-Potassium-Exchanging ATPase; D004229:Dithiothreitol