Nitric oxide prevents myoglobin/tert-butyl hydroperoxide-induced inhibition of Ca2+ transport in skeletal and cardiac sarcoplasmic reticulum.

Interaction of hydrogen peroxide or organic hydroperoxides with hemoproteins is known to produce oxoferryl hemoprotein species that act as very potent oxidants. Since skeletal and cardiac muscle cells contain high concentrations of myoglobin this reaction may be an important mechanism of initiation or enhancement of oxidative stress, which may impair their Ca2+ transport systems. Using skeletal and cardiac sarcoplasmic reticulum (SR) vesicles, we demonstrated by EPR the formation of alkoxyl radicals and protein-centered peroxyl radicals in the presence of myoglobin (Mb) and tert-butyl hydroperoxide (t-BuOOH). The low temperature EPR signal of the radicals was characterized by major feature at g = 2.016 and a shoulder at g = 2.036. In the presence of SR vesicles, the magnitude of the protein-centered peroxyl radical signal decreased, suggesting that the radicals were involved in oxidative modification of SR membranes. This was accompanied by SR membrane oxidative damage, as evidenced by accumulation of 2-thiobarbituric acid-reactive substances (TBARS) and the inhibition of Ca2+ transport. We have shown that nitric oxide (NO), reacting with redox-active heme iron, can prevent peroxyl radical formation activated by Mb/t-BuOOH. Incubation of SR membranes with an NO donor, PAPA/NO (a non-thiol compound that releases NO) at 200-500 microM completely prevented the t-BuOOH-dependent production of peroxyl radicals and formation of TBARS, and thus protected against oxidative inhibition of Ca2+ transport.