Exercise promotes a subcellular redistribution of calcium-stimulated protease activity in striated muscle.

The aims of this study were (i) to investigate whether the contractile activity associated with running increases calcium-stimulated, calpastatin-inhibited protease activity (calpain-like) in a time-dependent manner and (ii) to determine whether the changes, if any, are proportionately distributed between soluble (cytosolic) and particulate (bound) fractions of striated muscle in vivo. Calcium-dependent, calpastatin-inhibited caseinolysis (i.e., calpain-like activity) was measured in control and exercised rats (25 m/min, 0% grade) at 2, 5, 15, 30, and 60 min. Total calpain-like activity in skeletal muscle increased by 26% (13.2 +/- 1.3 vs. 17.9 +/- 2.2 U/g wet wt.) (p < 0.05) after running (60 min), accompanied by an increased activity in the particulate fraction. In cardiac muscle, exercise (60 min) increased total calpain-like activity by 33% (p < 0.05), which was attributable to increases in both the cytosolic and particulate fractions. Both tissues responded with an early (2-5 min) activation of total calpain-like activity (p < 0.05), supported by early increases for particulate fractions from skeletal muscle; whereas for cardiac muscle, a noticeable early drop (p < 0.05) occurred in the particulate fraction. Minimal changes were observed for total, cytosolic, and particulate fractions of noncontracting tissue (i.e., liver). The results of this study support the hypothesis that the total calpain-like activity increases associated with level running occur early on with exercise and that the increases are accompanied by changes in the redistribution of soluble to particulate fractions. The changes would set the stage for enhanced rates of protein degradation known to occur in striated muscle with exercise.

Striated muscle calcium-stimulated cysteine protease (calpain-like) activity promotes myeloperoxidase activity with exercise.

An inflammatory response triggered by neutrophil accumulation into muscle tissue is thought to occur with exercise-induced muscle damage. To investigate the relationship between Ca2+-stimulated proteolysis (calpain-like activity) and neutrophil accumulation [myeloperoxidase (MPO) activity], cardiac and plantaris muscles from rats (n = 10) completing 1 h exercise (25 m/min) were investigated. Exercise promoted increases (P<0.05) in both calpain-like and MPO activities; ranging from 2.79 to 58.9 U/g wet weight (ww) and 0.03 to 4.88 U/g ww respectively. Pearson's correlational analysis (r) on calpain-like and MPO activities for cardiac and plantaris muscle data were 0.97 (P<0.001) and 0.68 (P<0.05) respectively, with a combined r of 0.83 (P<0.001) for both muscles across all conditions. To investigate further the extent to which calpain-like activity may promote neutrophil accumulation, another exercise group (n = 5) was pre-injected with the cysteine protease inhibitor, E64c, 1 h before exercise. Administration of E64c lowered calpain-like and MPO activities by 66% and 56% respectively (average from both muscles). From these results it is concluded that a relationship exists between Ca2+-stimulated proteolysis and neutrophil accumulation into striated muscle with exercise, and that the calpain system is involved in localizing the neutrophilic response with exercise.