METABOLIC END-PRODUCTS INHIBIT SARCOPLASMIC-RETICULUM CA2+ RELEASE AND [H-3] RYANODINE BINDING

Sarcoplasmic reticulum (SR) Ca2+ release channel function is modified by ligands (Mg2+, Ca2+ ATP, and H+) that are generated during a bout of exercise. We have examined the effects of changing intracellular metabolites on Ca2+ release, [H-3]ryanodine binding, and single-Ca2+ release channel activity of SR isolated from white rabbit skeletal muscle. Increasing Mg2+ (from 0 to 4 mM) and decreasing pH (7.1-6.5) inhibited SR Ca2+ release and [H-3]ryanodine binding. In addition, increasing lactate concentrations from 2 to 20 mM inhibited [H-3]ryanodine binding to SR vesicles, inhibited SR Ca2+ release, and decreased the single-channel open probability. These findings suggest that intracellular modifications that disrupt excitation-contraction coupling and decrease Ca2+ transients will promote a decline in tension development and contribute to muscle fatigue. In addition, we show that hydrogen peroxide induces Ca2+ release and increases [H-3]ryanodine binding to its receptor, suggesting that reactive oxygen species produced during exercise may compromise muscle function by altering the normal gating of the SR Ca2+ release channel.