Neural influence on muscle hydrolase activity

Effects of myotoxins on skeletal muscle fibers

This review highlights various aspects of a number of experimental myological alterations, induced by different chemical toxicants, including anticholinesterase, colchicine, vincristine, chloroquine, tetanus toxin, botulinum toxin, reserpine and emetine. Despite their chemical diversity and mechanism(s) of action, it is evident from the data discussed here that remarkably different toxic agents exert quite similar effects and induce toxic myopathies. The latter include preferential involvement of slow-twitch red muscle, mitochondrial derangement, denervation-like alterations, formation of membranous whorls, tubular aggregates, autophagic vacuoles and axonal sprouts. The non-invasive experimental models discussed here are valuable in studying various aspects of myopathology in the absence of any mechanical damage to the innervating elements from neurons to axonal terminals.

Neurotoxicity of Adriamycin and misonidazole in the mouse

The neurotoxicity of the anticancer drug adriamycin was investigated in the peripheral nerve of the mouse. Injection of adriamycin into the sciatic nerve resulted in biochemical and morphologic signs of severe axonal degeneration. The biochemical evidence was based on marked increases in lysosomal enzyme activity. Acid protease and N-acetylglucosaminidase remained elevated for more than 70 days after injecting the drug. In contrast, local injection of the radiation-sensitizing drug misonidazole into the peripheral nerve failed to increase lysosomal enzyme activity.

Lysosomal and energy enzyme activities in hypertrophied rat soleus muscle after denervation

Muscle hypertrophy was induced in the soleus muscle of young rats by tenotomy of the gastrocnemius and plantaris muscles. Three and 7 days afterwards the sciatic nerve was sectioned. The loss of weight of muscles subjected to this combined procedure three days after denervation was 30-40%. Lysosomal enzyme activities (acid phosphatase, alpha-glucosidase, beta-galactosidase and N-acetyl-beta-D-glucosaminidase) and energy enzyme activities (lactate dehydrogenase, LDH, triose-3-phosphate dehydrogenase, TPDH , D-hexokinase, HK and citrate synthase, CS) were determined 3 days after denervation, 3, 7 and 10 days after hypertrophy had been induced and 3 days after denervation of hypertrophying muscles on day 3 and 7. Normal non-operated rats of corresponding body weight served as controls and their enzyme activities were estimated on the same day. In the course of muscle hypertrophy, the 4 lysosomal enzyme activities increased progressively. Although 3 days' denervation of control muscles did not alter lysosomal enzyme activities, denervation of hypertrophying muscles greatly enhanced the activity of these enzymes. Enzymes of energy metabolism were affected to a lesser degree. The results suggest that denervation of hypertrophying muscles causes more extreme changes in muscle weight and lysosomal enzyme activities than denervation alone. The possible implications of this finding are discussed in relation to the rapid atrophy.

Immunocytochemical studies of cathepsin D in human skeletal muscle

The distribution of cathepsin D, an acidic endopeptidase, was localized by immunocytochemistry in human skeletal muscle obtained from 34 persons with a variety of neuromuscular disorders. Normal human skeletal muscle contained small amounts of cathepsin D, all of which was found close to the sarcolemmal membrane. Immunoreactive cathepsin D was present in the cytoplasm of many infiltrating phagocytic cells and was increased in skeletal muscle fibers from patients with muscular dystrophies, inflammatory myopathies, rhabdomyolysis, acid maltase deficiency, and neurogenic atrophy. In cases of Duchenne type muscular dystrophy, the increase in cathepsin D was especially prominent in small regenerating fibers, in which it was visualized at the ultrastructural level in lysosome-like organelles and extralysosomal locations. The function of cathepsin D in skeletal muscle is unclear, but the present findings suggest a possible role in muscle regeneration and repair. Such a role would necessitate careful selection of drugs which interfere with proteolytic activity if they are to be used as therapeutic agents in treating neuromuscular diseases.

Neurotoxin-induced hydrolase activity in peripheral nerve

The effect of neurotoxins which block axonal transport or impulse transmission was examined on sciatic nerve hydrolase activity. Subepineural injection of batrachotoxin (BTX) or colchicine resulted in a 4-9 fold increase in acid protease and N-acetylglucosaminidase activity with a smaller increase in acid phosphatase activity. The enzyme remained elevated for up to 48 days. Similar injections of tetrodotoxin (TTX) led to a relatively small increase in the activity of these enzymes which returned to normal values within two days. The prolonged increase in hydrolase activity produced by BTX and colchicine suggests that blockade of axonal transport may be mediated by nerve necrosis.