Calcium-dependent and calcium-independent protease activities in skeletal muscle during sepsis

Sepsis was produced in rats by implanting into their abdominal cavities fecal pellets containing Escherichia coli (10(2) colony-forming units [CFU]) and Bacteroides fragilis (10(4) CFU). Control rats were implanted with sterile pellets. A febrile response and hyperlactacidemia marked the onset of the septic injury. Control and septic rats were killed 24 and 48 hr after implantations, and posterior leg muscles were removed. Muscles were homogenized to prepare soluble fractions containing calcium-independent lysosomal (cathepsins B and L) and calcium-dependent cytosolic (calpain) proteases. Cathepsin and calpain activities were then assayed using standard procedures. There were no alterations in cathepsins B or L activities during sepsis. Calpain activity in septic muscle was significantly higher than that in control muscles. In vitro calpain sensitivity to Ca2+ was also higher in septic muscle than in controls. The cysteine protease inhibitor leupeptin caused a quantitatively greater inhibition of calpain activity in septic than in control muscles. These data indicate that whereas sepsis has no effect on Ca(2+)-insensitive lysosomal proteases, it is associated with an elevation of the Ca(2+)-dependent cytosolic protease activity.