HYDROGEN-PEROXIDE STIMULATES THE CA2+ RELEASE CHANNEL FROM SKELETAL-MUSCLE SARCOPLASMIC-RETICULUM

Hydrogen peroxide (H2O2) at millimolar concentrations induces Ca2+ release from actively loaded sarcoplasmic reticulum vesicles and induces biphasic [H-3]ryanodine binding behavior. High affinity [H-3]ryanodine binding is enhanced at concentrations hom 100 mu M to 10 mM (3-4-fold). At H2O2 concentrations greater than 10 mM, equilibrium binding is inhibited. H2O2 decreased the k(d) for [H-3]ryanodine binding by increasing its association rate, while having no effect on the rate of dissociation of [H-3]ryanodine from its receptor. H2O2 (1 mM) also reduced the EC(50) for Ca2+ activation hom 632 nM to 335 nM. These effects were completely abolished in the presence of catalase, ruthenium red, and/or Mg2+ (mM) H2O2-stimulated [H-3]ryanodine binding is not further enhanced by either doxorubicin or caffeine. The direct interaction between H2O2 and the Ca2+ release mechanism was further demonstrated in single-channel reconstitution experiments. Peroxide, at submillimolar concentrations, activated the Ca2+ release channel following fusion of a sarcoplasmic reticulum vesicle to a bilayer lipid membrane. At millimolar concentrations of peroxide, Ca2+ channel activity was inhibited. Peroxide stimulation of Ca2+ channel activity was reversed by the thiol reducing agent dithiothreitol. Paralleling peroxide induced activation of ryanodine binding, Ca2+ transport, and single Ca2+ channel activity, it was observed that the ryanodine receptor formed large disulfide-linked protein complexes that dissociated upon addition of dithiothreitol.