Effect of oxidants on Na,K,ATPase and its reversal

Abstract

Ischemia-reperfusion heart cell injury may be mediated, at least in part, through the generation of oxy radicals. Therefore, mechanisms of action of two oxidants on a membrane model, partially purified Na,K,ATPase, were investigated. Effects of H2O2, an oxygen intermediate postulated to play a primary role in reperfusion injury, on the function of the enzyme were time-dependent and potentiated by Fe ions. The inhibition of enzyme activity was prevented by chelators, but not by hydroxyl radical scavengers. The results support the view that the possible mode of enzyme modification involves H2O2-derived, Fe ion-catalyzed, localized ("site-specific") hydroxyl radical formation. The action of hypochlorous acid (HOCl), a powerful oxidant postulated to be produced by activated neutrophils, was quantitatively similar to that of H2O2 plus Fe ions in causing enzyme dysfunction. This is partly because relatively large doses of oxidants were required, due to the presence of physiological anti-oxidant defense mechanisms in the membrane. Although a combination of deferoxamine (Fe ion chelator) and dithiothreitol (DTT) (sulfhydryl reducing agent) was most effective in preventing the enzyme modification, once enzyme inactivation by oxidants is in progress, deferoxamine plus DTT could only arrest further deterioration of the enzyme function. Therefore, the oxidant-induced change in membrane dysfunction advances with time; the advance can be stalled, but the enzyme activity cannot be restored to normal.

The effect of oxygen free radicals on calcium current and dihydropyridine binding sites in guinea‐pig ventricular myocytes

“…However, previous results indicate that the hydroxyl radical is the main one responsible for the electrophysiological damage caused by DHF (Jabr & Cole, 1993). It has been suggested that oxidative modification of sulphydryl groups of channels or ion transporters (Yanagishita et al, 1989;Matsouka et al, 1990;Eley et al, 1991;Jabr & Cole, 1995) Cerbai et al, 1991). However it must be recalled that in intact preparations lipid peroxidation is shown to occur with demonstrable changes in electrical activity (Nakaya et al, 1987).…”

“…However, previous results indicate that the hydroxyl radical is the main one responsible for the electrophysiological damage caused by DHF (Jabr & Cole, 1993). It has been suggested that oxidative modification of sulphydryl groups of channels or ion transporters (Yanagishita et al, 1989;Matsouka et al, 1990;Eley et al, 1991;Jabr & Cole, 1995) may be involved in the alterations caused by OFRs. It is possible that the decrease in DHP binding sites is due to a similar modification in sulphhydril groups somehow associated with the channel.…”

“…It is consequently clear that the increase in cellular calcium loading caused by OFRs is not due to an increase in calcium flux through calcium channels, but involves other pathways. Inactivation by OFRs of the sarcolemmal Ca2+ pump, Na', K+-ATPase, and sarcoplasmic reticulum Ca2+-ATPase have been demonstrated (Kim & Akera, 1987;Kaneko et al, 1989a;1990;Yanagishita et al, 1989;Matsouka et al, 1990;Eley et al, 1991) and all these mechanisms are involved in intracellular calcium homeostasis. Furthermore, here we confirm that OFR cause a decrease in the outward potassium current IK, which is the main determinant of the prolongation of the action potential duration caused by OFRs (Cerbai et al, 1991).…”

Role of Oxidative Stress in Ischemia–Reperfusion-Induced Changes in Na+,K+-ATPase Isoform Expression in Rat Heart

“…Depressed Na + ,K + -ATPase activity is seen after the treatment of cardiac sarcolemma with hypochlorous acid (17,19), hydrogen peroxide (H 2 O 2 ) (21,24,29), and xanthine plus xanthine oxidase (XXO) (28,32). Furthermore, the XXO-induced decrease in sodium pump activity was prevented by treatment of the sarcolemmal preparations with superoxide dismutase (SOD), either alone or in combination with catalase (CAT) (28).…”

Autocrine/paracrine modulation of baroreceptor activity after antidromic stimulation of aortic depressor nerve in vivo

“…The Na + pump mediates transient post-excitatory depression of activity in a variety of sensory nerves (Nakajima & Takahashi, 1966; Sokolove & Cooke, 1971) including baroreceptor terminals (Saum et al, 1976), and its activation is enhanced by H 2 O 2 (Matsuoka et al, 1990; Rounds et al, 1998). The stability of H 2 O 2 may account for the relatively prolonged period of inhibition of baroreceptor activity observed after antidromic stimulation of ADN.…”