MECHANISM OF DEPRESSION IN CARDIAC SARCOLEMMAL NA-K+-ATPASE BY HYPOCHLOROUS ACID()

Oxidative stress during pathological conditions such as ischemia-reper fusion is known to promote the formation of hypochlorous acid (HOCl) i n 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. Charac terization of Na+-K+-ATPase activity in the presence of different conc entrations of MgATP revealed a decrease in the maximal velocity (V-max ) value, without a change in affinity for MgATP on treatment of SL mem branes with 0.1 mM HOCl. The V-max value of Na+-K+-ATPase, when determ ined in the presence of different concentrations of Na+, was also decr eased, but affinity for Na+ was increased when treated with HOCl. Form ation of acylphosphate by SL Na+-K+-ATPase was not affected by HOCl. S catchard plot analysis of [H-3]ouabain binding data indicated no signi ficant change in the affinity or maximum binding capacity value for ou abain binding following treatment of SL membranes with HOCl. Western b lot analysis of Na+-K+-ATPase subunits in HOCl-treated SL membranes sh owed a decrease (34 +/- 9% of control) in the beta(1)-subunit without any change in the alpha(1)- or alpha(2)-subunits. These data suggest t hat the HOCl-induced decrease in SL Na+-K+-ATPase activity may be due to a depression in the beta(1)-subunit of the enzyme.