The effects of eccentric contraction on myofibrillar proteins in rat skeletal muscle

Abstract

The present study investigated the effects of eccentric muscle contractions (ECC) on the content of myofibrillar proteins (my-proteins) and the catalytic activity of myofibrillar ATPase (my-ATPase) in skeletal muscles. Rat extensor digitorum longus and tibialis anterior muscles were exposed to 200-repeated ECC or isometric contractions (ISC) and used for measures of force output and for biochemical analyses, respectively. Whereas in ISC-treated muscles, full restoration of tetanic force was attained after 2days of recovery, force developed by ECC-treated muscles remained depressed (P<0.05) after 6days. The total my-protein content and the relative content of myosin heavy chain (MHC) in total my-proteins were unaltered during 4days of recovery after ECC, but fell (P<0.05) to 55.9 and 63.4% after 6days of recovery, respectively. my-ATPase activity expressed on a my-protein weight basis was unaltered immediately after ECC. However, it decreased (P<0.05) to 75.3, 45.3, and 49.3% after 2, 4 and 6days of recovery, respectively. Total maximal calpain activity measured at 5mM Ca(2+) was significantly augmented (P<0.05) after 2days of recovery, reaching a level of threefold higher after 6days. These alterations were specific for ECC and not observed for ISC. These results suggest that depressions in my-ATPase activity contribute to ECC-induced decreases in force and power which can take a number of days to recover.