Hydrogen peroxide and hydroxyl radical mediation of activated leukocyte depression of cardiac sarcoplasmic reticulum. Participation of the cyclooxygenase pathway.

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Abstract
Human peripheral blood leukocytes, activated by phorbol myristate acetate, disrupt canine sarcoplasmic reticulum calcium transport, in vitro, by an oxygen-derived free radical mechanism. Activated leukocytes significantly depress Ca++ uptake activity and Ca++ -stimulated, Mg++ -dependent ATPase activity. The depression is completely inhibited by sodium-azide (0.1 mM) or the combination of superoxide dismutase (10 micrograms/ml) and catalase (10 micrograms/ml). Exogenous hydrogen peroxide (0.441-4.41 mM) uncoupled Ca++ uptake activity from ATP hydrolysis, and this effect was inhibited by catalase. Mannitol alone did not inhibit the effects of activated leukocytes, but superoxide plus mannitol (20-100 mM) resulted in normal ATPase activity, while Ca++ uptake remained depressed. In the presence of indomethacin and ibuprofen, activated leukocytes depressed Ca++ uptake and had no effect on ATPase activity. 2-Amino-methyl-4-t-butyl-6-iodophenol (MK-447) further depressed Ca++ uptake and partially inhibited the effect on ATPase activity. Indomethacin plus catalase completely inhibited the effects of activated leukocytes on cardiac sarcoplasmic reticulum. We conclude, first, that activated leukocytes depress canine cardiac sarcoplasmic reticulum Ca++ transport by an oxygen-free radical mechanism with the generation of hydrogen peroxide and hydroxyl radical. In addition to the classical membrane NADPH oxidase system, significant oxygen radical generation can occur through the cyclooxygenase pathway of arachidonic acid metabolism, and seems to be responsible for the generation of the hydroxyl radical.