INTRACELLULAR EFFECTS OF FREE-RADICALS AND REACTIVE OXYGEN SPECIES INCARDIAC-MUSCLE

Oxygen-derived free radicals (FRs) and other reactive oxygen species ( ROS) have been implicated in the deleterious aspects of myocardial inf arction, neutrophil infiltration and post-ischaemic reperfusion. We st udied their actions on the main intracellular organelles of Ca-compart mentation and force production (the sarcoplasmic reticulum (SR) and my ofilaments) in rat heart preparations by using two forms of chemical ' skinning'. We recorded Ca2+-activated isometric tension or, in saponin -treated trabeculae where SR function is maintained, either tension al one or tension and [Ca2+] transients evoked by caffeine. A single, bri ef application of xanthine/xanthine oxidase (generating superoxide;O-. (2)-) rapidly and irreversibly inhibits Ca2+-activated force with a do se- and time-dependent action. The kinetics of residual force producti on are slowed. Rigor induction (by ATP withdrawal) before and during e xposure to O-.(2)- prevents this action, suggesting the O-.(2)--sensit ive site is occluded in rigor. Myofilament Ca-sensitivity and SR funct ion were unaffected by O-.(2)- or physiologically relevant [H2O2] (<10 mu M). Briefly applying 10-50 mu M hypochlorous acid (HOCl) increased Ca-sensitivity and resting tension, but reduced Ca-activated force, i n a manner consistent with 'rigor-like' crossbridges being involved. H OCl also provoked spontaneous Ca-release but reduced net SR Ca-uptake. Electron microscopy reveals that the myofilament lattice suffers a ch aracteristic disruption by HOCl but not by O-.(2)-. We conclude that F Rs and ROS associated with myocyte dysfunction, reperfusion and inflam mation could contribute to post-ischaemic myocardial dysfunction.