Oxidation of sarcoplasmic reticulum Ca(2+)-ATPase induced by high-intensity exercise

Ca(2+)-ATPase and Ca(2+)-pumping activities by the sarcoplasmic reticulum (SR) and the amounts of sulphydryl and carbonyl groups contained in the SR protein were examined in the superficial portion of the gastrocnemius and vastus lateralis muscles of the rat after high-intensity treadmill runs to exhaustion (average time to exhaustion: 363 s). Exercise at the estimated maximal O(2) uptake rate led to 16% and 34% reductions in SR Ca(2+)-ATPase activity ( P<0.01) and Ca(2+) uptake rate ( P<0.01), respectively. The carbonyl group content in SR Ca(2+)-ATPase, assessed by immunoblotting analysis, was increased by 127% after exercise ( P<0.05), while the sulphydryl group content in the purified SR fraction was unchanged. Consistent with the unchanged sulphydryl group content, treatment of homogenates with dithiothreitol, the disulphide reducing reagent, failed to restore the decreased catalytic activity of SR Ca(2+)-ATPase in exercised muscles. These findings show clearly that high-intensity, exhaustive exercise causes oxidation of SR Ca(2+)-ATPase protein and suggest that oxidation of amino acids, other than cysteine, in the SR Ca(2+)-ATPase may be responsible, at least in part, for exercise-induced inactivation of this enzyme.