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

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.

Glycolytic inhibition and calcium overload as consequences of exogenously generated free radicals in rabbit hearts.

“…Exogenous free radicals would be expected to enhance cellular calcium loading by the known inhibition ofNa'-K+ ATPase in the surface membrane and of Ca2+-ATPase in both the sarcolemma and the sarcoplasmic reticulum (20,22,23,(62)(63)(64)(65). Free radicals are also capable ofinjuring mitochondrial Ca2+-ATPase (34).…”

Medical and Cellular Implications of Stunning, Hibernation, and Preconditioning

“…Transient exposure to ROS has also been found to decrease the responsiveness of myofilaments to Ca 2ϩ58 and to impair the function of sarcoplasmic reticulum. 59 Investigation of the manner in which ROS perturb Ca 2ϩ homeostasis and/or Ca 2ϩ responsiveness is important not only because it should elucidate the pathogenesis of stunning but also because it may reconcile the oxyradical and Ca 2ϩ hypotheses of stunning into one pathogenic mechanism (Fig 1A).…”

Myocardial reperfusion: a double-edged sword?

“…Activated human neutrophils depress both the uptake of Ca++ by myocytes and the activity of Ca++-stimulated, Mg++-dependent ATPase, which are actions that can be prevented by the combination ofsuperoxide dismutase and catalase, and which therefore are presumably caused by oxygen-derived free radicals (56). Endoperoxide intermediates, resulting from the conversion of arachidonic acid, also lead to the production ofoxygen-free radicals by leukocytes and other cell types in the heart (57).…”