Free oxygenated radicals frequently are involved in
cardiac arrhythmias and contractility disorders during postischemic reperfusion. The aim of this study was to determine the effects of
hydroxyl radicals (.
OH) in vitro on myofibrillar Ca-
adenosinetriphosphatase (
ATPase), on the redox state of
thiol groups and the electrophoretic pattern of myofibrillar
proteins from rat heart. Myofibrils were treated up to 60 min by .
OH generated with 0.3 mM H2O2 and 0.1 mM Fe2+. After a 60-min treatment with .
OH, the measurement of
thiol groups failed to show any oxidation. On the contrary,
ATPase activity and electrophoretic pattern were affected dramatically by treatment with .
OH. For all Ca2+ concentrations,
ATPase was increased
after treatment with .
OH, but
ATPase activation when Ca2+ rose from pCa 8 to pCa 4.5 was only 92% after 30 min of incubation rather than 226% for untreated myofibrils. The electrophoretic analysis of myofibrillar
proteins showed a decrease in
myosin heavy chain and formation of aggregates in treated myofibrils. All of these effects were reduced when incubation was performed in the presence of
mannitol, a specific scavenger of .
OH. No effect was observed with 0.1 mM Fe2+ alone or with 0.3 mM H2O2. The action of .
OH was very fast to the extent that the effects were observed after only 15 s of incubation. The results reported in the present study may be related to the impaired relaxation and
contracture described in vivo within the first minutes of a postischemic reperfusion and before any change in
calcium homeostasis.