Biochemical and ultrastructural effects of chloroquine on horseradish peroxidase uptake and lysosomal enzyme activities in innervated and denervated mouse skeletal muscle.

The effects of chloroquine treatment on horseradish peroxidase (HRP) uptake and lysosomal enzyme activities in innervated and denervated mouse skeletal muscle have been studied using biochemical, histochemical and ultrastructural techniques. Chloroquine treatment caused a large (59-101%) increase in the activity of cathepsin D in both innervated and denervated muscle. The activity of N-acetyl-beta-D-glucosaminidase also increased slightly in denervated muscle. No effect was observed on acid phosphatase activity. The in vivo uptake of HRP in innervated and denervated muscle was unaffected by chloroquine treatment. The results show that the activities of certain lysosomal enzymes may increase in skeletal muscle without an increase in endocytic activity. This is discussed in comparison to what is seen in denervated and dystrophic muscle. Histochemical and ultrastructural studies showed the HRP uptake to occur segmentally in denervated muscle fibres from untreated as well as chloroquine-treated animals. Ultrastructurally the peroxidase-positive phagosomes occurring in these segments were found to contain increased levels of undegraded material after chloroquine treatment suggesting that these phagosomes are of a lysosomal nature and also participate in autophagic processes.