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 acti vity associated with running increases calcium-stimulated, calpastatin-inhi bited protease activity (calpain-like) in a time-dependent manner and (ii) to determine whether the changes, if any, are proportionately distributed b etween soluble (cytosolic) and particulate (bound) fractions of striated mu scle 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 ske letal 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 t he particulate fraction. In cardiac muscle, exercise (60 min) increased tot al calpain-like activity by 338 (p < 0.05), which was attributable to incre ases in both the cytosolic and particulate fractions. Both tissues responde d with an early (2-5 min) activation of total calpain-like activity (p < 0. 05), supported by early increases for particulate fractions from skeletal m uscle; whereas for cardiac muscle, a noticeable early drop (p < 0.05) occur red in the particulate fraction. Minimal changes were observed for total, c ytosolic, and particulate fractions of noncontracting tissue (i.e., liver). The results of this study support the hypothesis that the total calpain-li ke activity increases associated with level running occur early on with exe rcise and that the increases are accompanied by changes in the redistributi on of soluble to particulate fractions. The changes would set the stage for enhanced rates of protein degradation known to occur in striated muscle wi th exercise.