Satoshi Matsunaga

Alterations in in vitro function and protein oxidation of rat sarcoplasmic reticulum Ca2+‐ATPase during recovery from high‐intensity exercise

The hypothesis tested in this study was that the extent to which sarcoplasmic reticulum (SR) Ca2+‐ATPase is oxidized would correlate with a decline in its activity. For this purpose, changes in the SR Ca2+‐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 Ca2+‐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 Ca2+‐uptake rate, and the proportional alteration in these two variables resulted in no change in the ratio of Ca2+‐uptake rate to Ca2+‐ATPase activity. The contents of SR Ca2+‐ATPase protein and sulfhydryl groups in microsomes were unchanged after exercise and during recovery periods. In contrast, the content of carbonyl groups in SR Ca2+‐ATPase behaved in an opposite manner to that of SR Ca2+‐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 Ca2+‐ATPase is responsible, at least in part, for a decay in the SR Ca2+‐pumping function produced by high‐intensity exercise and imply that oxidized proteins may be repaired during recovery from exercise.

Role of calpain in eccentric contraction-induced proteolysis of Ca2+-regulatory proteins and force depression in rat fast-twitch skeletal muscle

The aim of this study was to examine the in vivo effects of eccentric contraction (ECC) on calpain-dependent proteolysis of Ca2+-regulatory proteins and force production in fast-twitch skeletal muscles. Rat extensor digitorum longus muscles were exposed to 200 repeated ECC in situ and excised immediately [recovery 0 (REC0)] or 3 days [recovery 3 (REC3)] after cessation of ECC. Calpain inhibitor (CI)-treated rats were intraperitoneally injected with MDL-28170 before ECC and during REC3. Tetanic force was markedly reduced at REC0 and remained reduced at REC3. CI treatment ameliorated the ECC-induced force decline but only at REC3. No evidence was found for proteolysis of dihydropyridine receptor (DHPR), junctophilin (JP)1, JP2, ryanodine receptor (RyR), sarcoplasmic reticulum Ca2+-ATPase (SERCA)1a, or junctional face protein-45 at REC0. At REC3, ECC resulted in decreases in DHPR, JP1, JP2, RyR, and SERCA1a. CI treatment prevented the decreases in DHPR, JP1, and JP2, whereas it had little effect on RyR and SERCA1a. These findings suggest that DHPR, JP1, and JP2, but not RyR and SERCA1a, undergo calpain-dependent proteolysis in in vivo muscles subjected to ECC and that impaired function of DHPR and/or JP might cause prolonged force deficits with ECC.NEW & NOTEWORTHY Calpain-dependent proteolysis is one of the contributing factors to muscle damage that occurs with eccentric contraction (ECC). It is unclear, however, whether calpains account for proteolysis of Ca2+-regulatory proteins in in vivo muscles subjected to ECC. Here, we provide evidence that dihydropyridine receptor and junctophilin, but not ryanodine receptor and sarcoplasmic reticulum Ca2+-ATPase, undergo calpain-dependent proteolysis.

No relationship between enzyme activity and structure of nucleotide binding site in sarcoplasmic reticulum Ca2+‐ATPase from short‐term stimulated rat muscle

Aim:  We examined whether structural alterations to the adenine nucleotide binding site (ANBS) within sarcoplasmic (endo) reticulum Ca2+‐ATPase (SERCA) would account for contraction‐induced changes in the catalytic activity of the enzyme as assessed in vitro.

Structure of sarcoplasmic reticulum and activity-induced alteration in its function

Repeated contractions of skeletal muscle lead to a decline of force known as fatigue. ule exact cause of muscular fatigue probably involves numerous factors which influence force production in a manner dependent on muscle丘ber type and activation pattern. However, a growing amount of evト dence implicates alteration of intracellular Ca2 * handling as a major contributor to fatigue. These changes are known to occur secondary to reductions in the rates of Ca2+ uptake and release by the sarcoplasmic reticulum (SR). In this brief review, we focus on two major aspects: 1 ) molecular mechanisms of the Ca2 + uptake and release process, focusing on Ca2+-ATPase protein and the ryanodine receptor; and 2 ) several factors that may be responsible for dysfunction of the SR resulting from contractile activity. Factors that might account for diminished function of the SR include a fall in internal pH, increased Ca 2 * concentration, modification by reacdve oxygen species, depletion of high-energy phosphate, and accumulation of inorganic phosphate.