Pitfalls in the histochemical demonstration of alpha-glucan phosphorylase activity in glycogen-depleted skeletal muscle fibres.

In the present communication, an investigation is described into the reliability of histochemical methods for the demonstration of alpha-glucan phosphorylase activity in glycogen-depleted skeletal muscle fibres. Human skeletal muscles with glycogen-depleted fibres from patients with diseases of the neuromuscular system and from subjects who had suffered from malignant hyperthermia were used for the study. The location of phosphorylase activity and glycogen was demonstrated with histochemical techniques. Biochemical techniques were used to assay the activity of phosphorylase and the content of glycogen. Biochemical determinations of phosphorylase activity did frequently not reveal significant differences between glycogen-depleted and non-depleted skeletal muscle fibres. In contrast, all histochemical methods investigated, showed little or no phosphorylase activity in the glycogen depleted fibres, indicating that none of the existing histochemical methods revealed reliable staining results in these fibres. Owing to the invalid staining results of the histochemical methods for glycogen-depleted muscle fibres, it is necessary that for metabolic studies a biochemical assay for phosphorylase activity is also to be performed.