Role of calpain in eccentric contraction-induced proteolysis of Ca-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 Ca-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 Ca-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. 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 Ca-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 Ca-ATPase, undergo calpain-dependent proteolysis.