Alterations in in vitro function and protein oxidation of rat sarcoplasmic reticulum Ca2+-ATPase during recovery from...

The hypothesis tested in this study was that the extent to which sarcoplasmic reticulum (SR) Ca(2+)-ATPase is oxidized would correlate with a decline in its activity. For this purpose, changes in the SR Ca(2+)-sequestering ability and the contents of carbonyl and sulfhydryl groups during recovery after exercise were examined in the superficial portions of vastus lateralis muscles from rats subjected to 5 min running at an intensity corresponding to maximal oxygen uptake (50 m min(-1), 10% gradient). A single bout of exercise elicited a 22.4% reduction (P < 0.05) in SR Ca(2+)-ATPase activity. The decreased activity progressively reverted to normal levels during recovery after exercise, reaching normal levels after 60 min of recovery. This change was paralleled by a depressed SR Ca(2+)-uptake rate, and the proportional alteration in these two variables resulted in no change in the ratio of Ca(2+)-uptake rate to Ca(2+)-ATPase activity. The contents of SR Ca(2+)-ATPase protein and sulfhydryl groups in microsomes were unchanged after exercise and during recovery periods. In contrast, the content of carbonyl groups in SR Ca(2+)-ATPase behaved in an opposite manner to that of SR Ca(2+)-ATPase activity. An approximately 80% augmentation (P < 0.05) in the carbonyl group content occurred immediately after exercise. The elevated carbonyl content decreased towards normal levels during 60 min of recovery. These results are strongly suggestive that oxidation of SR Ca(2+)-ATPase is responsible, at least in part, for a decay in the SR Ca(2+)-pumping function produced by high-intensity exercise and imply that oxidized proteins may be repaired during recovery from exercise.