Subcellular localization-dependent decrements in skeletal muscle glycogen and mitochondria content following short-term disuse in young and old men

Sep 23, 2010American journal of physiology. Endocrinology and metabolism

Loss of muscle energy stores and power units in specific cell areas after short rest in young and old men

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Abstract

Immobilization for 2 weeks reduced glycogen content in the inner myofibrils by 54% in both young and old men.

Glycogen content in the inner myofibrils decreased significantly, while glycogen in the other locations remained unchanged.
Mitochondria content also showed a localization-dependent decrease following immobilization.
Subsarcolemmal mitochondria decreased by 33%, while superficial intermyofibrillar mitochondria decreased by 20%.
The central intermyofibrillar mitochondria content did not change.
Both age groups exhibited similar patterns of adaptation in glycogen and mitochondria content due to immobilization.

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Previous studies have shown that skeletal muscle glycogen and mitochondria are distributed in distinct subcellular localizations, but the role and regulation of these subcellular localizations are unclear. In the present study, we used transmission electron microscopy to investigate the effect of disuse and aging on human skeletal muscle glycogen and mitochondria content in subsarcolemmal (SS), intermyofibrillar (IMF), and intramyofibrillar (intra) localizations. Five young (∼23 yr) and five old (∼66 yr) recreationally active men had their quadriceps muscle immobilized for 2 wk by whole leg casting. Biopsies were obtained from m. vastus lateralis before and after the immobilization period. Immobilization induced a decrement of intra glycogen content by 54% (P < 0.001) in both age groups and in two ultrastructurally distinct fiber types, whereas the content of IMF and SS glycogen remained unchanged. A localization-dependent decrease (P = 0.03) in mitochondria content following immobilization was found in both age groups, where SS mitochondria decreased by 33% (P = 0.02), superficial IMF mitochondria decreased by 20% (P = 0.05), and central IMF mitochondria remained unchanged. In conclusion, our findings demonstrate a localization-dependent adaptation to immobilization in glycogen and mitochondria content of skeletal muscles of both young and old individuals. Specifically, this suggests that short-term disuse preferentially affects glycogen particles located inside the myofibrils and that mitochondria volume plasticity can be dependent on the distance to the fiber border.

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Subcellular localization-dependent decrements in skeletal muscle glycogen and mitochondria content following short-term disuse in young and old men

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