H2O2 MODULATES TWITCH TENSION AND INCREASES P-O OF CA-2-MUSCLE( RELEASE CHANNEL IN FROG SKELETAL)

The effect of H2O2 was examined to elucidate the basis of muscle injur y after exercise. Exposure of single fibers to 1.5-6 mM H2O2, led to t witch potentiation followed by a marked decrease. Then, fibers contrac ted spontaneously. BAY K 8644 augmented twitch potentiation and slowed the decay of twitches. In 5 mM dithiothreitol (DTT), twitch potentiat ion and spontaneous contraction were not observed on H2O2 addition. Cy toplasmic application of 1.5-3 mM H2O2 to heavy sarcoplasmic reticulum (SR) vesicles incorporated into planar lipid bilayers increased the o pen probability of Ca2+ release channels, an effect reversed by DTT. W e investigated oxidation of sulfhydryl groups on proteins in SR membra ne by H,Og with -(7-dimethylamino-4-methyl-3-coumarinyl)maleimide. Pre treatment of light and heavy SR membranes with 1.5 mM H2O2 exponential ly increased fluorescence intensity. The time constant of the intensit y increase was increased markedly only in heavy SR in solution contain ing 50 mu M cytoplasmic Ca2+, so Ca2+ release was associated with prot ein oxidation by H2O2, Thus extracellular H2O2 probably acts by oxidiz ing sulfhydryls of proteins at two distinct sites: the dihydropyridine receptors, oxidation of which elicits potentiation and subsequent inh ibition of twitches, and Ca2+ release channels, whose oxidation elicit s spontaneous contraction, resulting in muscle dysfunction.