Immunocytochemical Localization of Cathepsin B in Degenerating Rat Skeletal Muscle Induced by a Local Anesthetic, Bupivacaine1

Abstract

Experimental acute degenerative changes in skeletal muscle accompanied by a drastic increase in cathepsins B&L were induced in rats by intramuscular injection of a local anesthetic, bupivacaine. Cathepsins B&L have been implicated in the rapid disappearance of muscle fibers. Degenerating muscle showed a spotty fluorescence when stained with antibodies against cathepsin B, indicating that the increased cathepsin B did not originate from the muscle itself, but from invading phagocytes. We report here results showing that cathepsin B of nonmuscle cell origin is involved in the breakdown of myofibrillar proteins in acute bupivacaine-induced muscle degeneration.

Demonstration of cathepsins B, H and L in xenografts of normal and Duchenne-muscular-dystrophy muscles transplanted into nude mice

“…It decreased sharply in normal muscle xenografts in the first week after transplantation and then tended to increase, but not significantly. There are reports that cathepsin activities derive primarily from macrophages and connective-tissue cells in many myopathies [44] and experimental myopathies [45,46]. We observed equal amounts of macrophages and connective-tissue cells in normal and DMD muscle xenografts 1 week after transplantation, as has been described previously [32,33].…”

<b>Effect of hind limb immobilization on the lysosomal enzyme activity in the rat skeletal </b><b>muscle </b>

“…The activity of all lysosomal enzymes (per mg soluble proteins) so far determined increased significantly in both lengthened and shortened soleus muscles irrespective of increase or decrease in protein contents. But the increase in these acid hydrolases by immobilization was milder than in a drug-induced degradation of skeletal muscle (7). Thus, we cannot explain the increased amount of proteins in soleus muscle after immobilization in a stretched position.…”

“…Since there have been few systematic reports on the activity of these proteases in immobilized muscle, we investigated whether all or any one of these proteases can be activated in immobilized mus-cle. Of most concern is whether the mechanism of atrophy due to immobilization is the same as that of drug-induced acute inflammatory muscle atrophy, in which appreciable increase in lysosomal enzyme activity derived from macrophages seems to play a major role in protein degradation (7).…”

“…Ca"-activated neutral protease at pH 7.5 were determined using azocasein as a substrate (7). The data were expressed as units/mg soluble proteins.…”

“…Recent reports have suggested the presence of phagocytes in degenerating muscle and indicated that invading macrophages contain relatively high amounts of lysosomal enzymes (7,12). Therefore, it is possible that increased lysosomal enzyme activity in the muscle homogenate was due to contamination by these macrophages.…”