Tissue specificity in cytochrome c oxidase deficient myopathy

Biopsied muscles were treated in 2 ways to demonstrate cytochrome c oxidase (CCO) activity on electron microscopy: (1) one to several muscle fibers were teased off the biopsy in buffer solution after glutaraldehyde fixation, (2) 20-30-microns thick cryostat sections were placed on precooled glass slides and fixed in glutaraldehyde solution at room temperature. After rinsing in buffer, the teased fibers and cryostat sections were stained with cytochrome c oxidase. In both procedures, almost all mitochondria in control muscle fibers stained positively. In CCO deficiency, the enzyme activity differed from tissue to tissue indicating marked tissue specificity. In the fatal infantile form enzyme activity in muscle fibers was absent, but present in fibroblasts, endothelial cells and smooth muscle arterial cells. The enzyme activity in other forms differed from cell to cell, but individual mitochondria in a given cell examined in cross-section showed uniform CCO activity, indicating that there was no intracellular mosaicism of enzyme positive and negative mitochondria.