The effect of an in vivo-injected thiol protease inhibitor, E-64-c, on the calcium-induced degeneration of myofilaments

The role of intracellular calcium-dependent proteinase(s) has been investigated in intact rat muscle. When calcium ions were introduced into intact muscle in vitro with ionophore A23187, Z-line loss and concomitant release of alpha-actinin into the medium were observed. The calcium-induced release of alpha-actinin was not diminished in the muscle with in vivo-injection of a thiol protease inhibitor, E-64-c. Intramuscular concentrations of E-64-c were also measured after pulse labeling with [3H]E-64-c followed by subcellular fractionation. Most of the inhibitor was localized in the cytosol, not in the lysosome. Therefore, we conclude that cytosolic as well as lysosomal proteinases in muscle are not inhibited by the in vivo labeling of the protease inhibitor (10 mg/kg).