Intracellular effects of free radicals and reactive oxygen species in cardiac muscle.
Oxygen-derived free radicals (FRs) and other reactive oxygen species (ROS) have been implicated in the deleterious aspects of myocardial infarction, neutrophil infiltration and post-ischaemic reperfusion. We studied their actions on the main intracellular organelles of Ca-compartmentation and force production (the sarcoplasmic reticulum (SR) and myofilaments) in rat heart preparations by using two forms of chemical 'skinning'. We recorded Ca(2+)-activated isometric tension or, in saponin-treated trabeculae where SR function is maintained, either tension alone or tension and [Ca2+] transients evoked by caffeine. A single, brief application of xanthine/xanthine oxidase (generating superoxide; O2-) rapidly and irreversibly inhibits Ca(2+)-activated force with a dose- and time-dependent action. The kinetics of residual force production are slowed. Rigor induction (by ATP withdrawal) before and during exposure to .O2- prevents this action, suggesting the .O2(-)-sensitive site is occluded in rigor. Myofilament Ca-sensitivity and SR function were unaffected by .O2- or physiologically relevant [H2O2] (< 10 microM). Briefly applying 10-50 microM hypochlorous acid (HOCl) increased Ca-sensitivity and resting tension, but reduced Ca-activated force, in a manner consistent with 'rigor-like' crossbridges being involved. HOCl also provoked spontaneous Ca-release but reduced net SR Ca-uptake. Electron microscopy reveals that the myofilament lattice suffers a characteristic disruption by HOCl but not by .O2-. We conclude that FRs and ROS associated with myocyte dysfunction, reperfusion and inflammation could contribute to post-ischaemic myocardial dysfunction.
D000818:Animals; D002118:Calcium / Q000502:physiology; D005609:Free Radicals; D006321:Heart / Q000187:drug effects*; D007425:Intracellular Membranes / Q000187:drug effects*; D008929:Mitochondria, Heart / Q000378:metabolism; D009200:Myocardial Contraction / Q000502:physiology; D009206:Myocardium / Q000648:ultrastructure; D051381:Rats; D017208:Rats, Wistar; D017382:Reactive Oxygen Species / Q000494:pharmacology*; D012146:Rest; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D013481:Superoxides / Q000378:metabolism
D005609:Free Radicals; D017382:Reactive Oxygen Species; D013481:Superoxides; D002118:Calcium