Related Experiment Videos
Changes in volume densities and distribution of mitochondria in rat skeletal muscle after chronic hypoxia
G J van Ekeren1, R C Sengers, A M Stadhouders
1Department of Cell Biology and Histology, University of Nijmegen, The Netherlands.
Abstract:
In order to test the hypothesis that subsarcolemmal aggregation of skeletal muscle mitochondria, as noted in some patients with mitochondrial myopathies, is caused by an impaired oxygen supply to mitochondria, we exposed two groups of rats to 8% O2 during 44 or 45 days. One group performed mild exercise, as did a normoxic control group. After hypoxia we investigated fibre type composition, fibre diameter and capillarity of soleus and extensor digitorum longus (e.d.l.) muscles. Mitochondrial volume densities were determined by morphometric analysis. In both e.d.l. and soleus muscle fibre type composition was unchanged and fibre diameter was reduced after hypoxia. Capillary network was unchanged, hence capillary density was increased in both muscles after hypoxia (P less than 0.05 in untrained soleus). Total mitochondrial volume density was increased in soleus muscle, which was due to an increase in the volume density of intermyofibrillar mitochondria (P less than 0.05 in the trained group), whereas the volume density of subsarcolemmal mitochondria decreased. In e.d.l. muscle the volume density of both intermyofibrillar and subsarcolemmal mitochondria decreased. We conclude that subsarcolemmal aggregation of mitochondria did not occur after chronic hypoxia. In soleus and e.d.l. muscle, different changes in the volume densities of mitochondria occurred. This may be related to the relative amounts of type I and type II fibres within these muscles.
Insights
Chronic hypoxia did not cause subsarcolemmal aggregation of skeletal muscle mitochondria. Instead, mitochondrial volume densities changed differently in soleus and extensor digitorum longus muscles, suggesting fiber type influences mitochondrial adaptation.
Area of Science:
- Exercise Physiology
- Mitochondrial Biology
- Cellular Adaptation
Background:
- Subsarcolemmal aggregation of skeletal muscle mitochondria is observed in mitochondrial myopathies.
- This aggregation is hypothesized to result from impaired oxygen supply to mitochondria.
Purpose of the Study:
- To investigate if chronic hypoxia leads to subsarcolemmal mitochondrial aggregation in skeletal muscle.
- To examine the effects of chronic hypoxia and exercise on mitochondrial distribution and muscle morphology.
Main Methods:
- Rats were exposed to chronic hypoxia (8% O2) for 44-45 days, with one group undergoing mild exercise.
- Muscle fiber type composition, diameter, capillarity, and mitochondrial volume densities (intermyofibrillar and subsarcolemmal) were analyzed using morphometric methods.
- Soleus and extensor digitorum longus (e.d.l.) muscles were examined.
Main Results:
- Chronic hypoxia reduced fiber diameter in both soleus and e.d.l. muscles.
- Capillary density increased in both muscles following hypoxia.
- Total mitochondrial volume density increased in soleus (due to intermyofibrillar increase), while subsarcolemmal density decreased; e.d.l. showed decreased density in both mitochondrial populations.
Conclusions:
- Chronic hypoxia does not induce subsarcolemmal mitochondrial aggregation in skeletal muscle.
- Differential changes in mitochondrial volume densities occurred between soleus and e.d.l. muscles, potentially linked to fiber type composition.
- The findings challenge the hypothesis that impaired oxygen supply directly causes subsarcolemmal mitochondrial aggregation.