MODIFICATION OF THE GATING OF THE CARDIAC SARCOPLASMIC-RETICULUM CA2-RELEASE CHANNEL BY H2O2 AND DITHIOTHREITOL()

The effect of hydrogen peroxide (H2O2) on the sheep cardiac sarcoplasm ic reticulum (SR) Ca2+-release channel has been investigated under vol tage-clamp conditions after incorporation of native membrane vesicles into planar phospholipid bilayers. In the presence of micromolar activ ating calcium concentrations on the cytosolic side of the membrane, H2 O2 (3-5 mM) increased open probability of the channels. H2O2 did not a ffect the conductance of the channel or the response to activating com pounds, such as ATP and caffeine. H2O2 did not alter the inhibitory re sponse to magnesium or the modification of channels by ryanodine. At s ubactivating calcium concentrations (similar to 45 pM) on the cytosoli c side of the membrane, 5 mM H2O2 was still able to open the channel. Analysis of single-channel open and closed lifetimes suggested that H2 O2 had a direct effect on the gating mechanism of the channel. Open pr obability of the SR Ca2+-release channel is reduced by millimolar conc entrations of dithiothreitol, a sulfhydryl-protecting compound, in a c oncentration-dependent manner. In conclusion, it is probable that H2O2 activates the SR Ca2+-release channel via an oxidation of cysteine th iol groups in the channel protein.