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Ultrastructural study of globular inclusions in human skeletal muscle mitochondria
Abstract:
Limb muscle biopsies from a patient with Luft's disease and a patient with a slowly progressive neuromuscular disorder since infancy revealed by conventional electron microscopy the presence of globular inclusions in the mitochondria as one of the most prominent morphological findings. Electron cytochemical studies on fresh tissue blocks showed no cytochrome c oxidase activity within the globular inclusions. The study of strontium uptake supported by either NAD and flavo-protein linked substrates in freshly isolated mitochondria fractions showed no electron-dense needles within the globular inclusions. Attempts to remove the inclusions with pepsin and with pronase on ultrathin sections failed but they were partially and totally removed by treatment of the sections with hydrogen peroxide. Freeze fracture studies showed the globular inclusions consisted of amorphous and lamellar material. The results suggest that the globular inclusions in muscle mitochondria may consist primarily of lipid.
Insights
Globular inclusions found in mitochondria of patients with Luft's disease and a progressive neuromuscular disorder may consist primarily of lipids, as indicated by specialized microscopy and chemical treatments.
Area of Science:
- Mitochondrial morphology and biochemistry
- Neuromuscular pathology
- Cellular inclusions
Background:
- Luft's disease and slowly progressive neuromuscular disorders can present with mitochondrial abnormalities.
- Globular inclusions within mitochondria are a notable morphological finding in these conditions.
Purpose of the Study:
- To characterize the composition and nature of globular inclusions found in muscle mitochondria.
- To differentiate these inclusions from other mitochondrial components and pathologies.
Main Methods:
- Conventional and freeze-fracture electron microscopy were employed.
- Electron cytochemistry for cytochrome c oxidase activity was performed.
- Strontium uptake studies with specific substrates were conducted.
- Enzymatic (pepsin, pronase) and chemical (hydrogen peroxide) treatments were used to analyze inclusion composition.
Main Results:
- Globular inclusions were observed in mitochondria of patients with Luft's disease and a progressive neuromuscular disorder.
- No cytochrome c oxidase activity was detected within the inclusions.
- Strontium uptake studies did not reveal electron-dense needles, suggesting absence of certain mineral deposits.
- Inclusions were resistant to pepsin and pronase but partially/totally removed by hydrogen peroxide.
- Freeze-fracture revealed amorphous and lamellar material within the inclusions.
Conclusions:
- The findings suggest that the globular inclusions are primarily composed of lipids.
- This lipid composition differentiates them from other known mitochondrial inclusions or structures.
- Understanding the nature of these inclusions may offer insights into the pathogenesis of these neuromuscular disorders.