A cytochemical study of acid phosphatase in dystrophic hamster muscle

The activity of acid phosphatase and the proportion of acid phosphatase-containing structures is significantly higher, it has been found, in unfixed 22 000 g (light mitochondrial/lysosomal) and 78 000 g (heavy microsomal) subcellular fractions of dystrophic hamster muscle than in the corresponding fractions of normal muscle. Most of the acid phosphatase activity in the 22 000 g fraction of dystrophic muscle seems to arise from vesicular structures comparable to dicytosomes rather than to lysosomes. Similarly, the bulk of the activity in the 78 000 g fraction appears to originate from the sarcoplasmic reticulum and membrane fragments. In sections of fixed dystrophic gastroenemii, acid phosphatase is largely localized in distended vesicular structures in mitochondrial-rich fibers (type I?) when cytidine 5-monophosphate or β-glycerophosphate is used as the substrate. Such structures are invariably associated with residual material (membrane whorls and lipofuscin) and are most commonly situated at the poles of central nuclei. Their various planes of section suggest that they might be part of a tortuous tubular system. Primary lysosomes are also occasionally seen in muscle fibers but these are situated near Golgi stacks at central and peripheral nuclei and are easily distinguishable from the acid phosphatase-positive tubular elements. The tubular structures are absent in sections of normal muscle, although acid phosphatase-reactive vesicular structures and membrane fragments are present in small amounts in the 22 000 and 78 000 g subcellular fractions of such muscle. From these observations, it is postulated that, in dystrophic muscle fibers, acid phosphatase is first synthesized and concentrated in the sarcoplasmic reticulum as part of a response to focal degeneration within the fibers. The portion of sarcoplasmic reticulum containing the enzyme then becomes distended and appears to envelop the initiators of the degeneration.