STRIATED-MUSCLE CALCIUM-STIMULATED CYSTEINE PROTEASE (CALPAIN-LIKE) ACTIVITY PROMOTES MYELOPEROXIDASE ACTIVITY WITH EXERCISE

An inflammatory response triggered by neutrophil accumulation into mus cle tissue is thought to occur with exercise-induced muscle damage. To investigate the relationship between Ca2+-stimulated proteolysis (cal pain-like activity) and neutrophil accumulation [myeloperoxidase (MPO) activity], cardiac and plantaris muscles from rats (n = 10) completin g 1 h exercise (25 m/min) were investigated. Exercise promoted increas es (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. Pea rson's correlational analysis (r) on calpain-like and MPO activities f or 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 muscle s across all conditions. To investigate further the extent to which ca lpain-like activity may promote neutrophil accumulation, another exerc ise group (n = 5) was pre-injected with the cysteine protease inhibito r, E64c, I h before exercise. Administration of E64c lowered calpain-l ike and MPO activities by 66% and 56% respectively (average from both muscles). From these results it is concluded that a relationship exist s between Ca2+-stimulated proteolysis and neutrophil accumulation into striated muscle with exercise, and that the calpain system is involve d in localizing the neutrophilic response with exercise.