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Scanning electron-microscopic studies on the three-dimensional structure of mitochondria in the mammalian red, white
Abstract:
The three-dimensional structure and arrangement of mitochondria in the red, white and intermediate striated muscle fibers of the rat were examined under a field-emission type scanning electron microscope after removal of cytoplasmic matrices by means of the Osmium-DMSO-Osmium procedure. Beneath the sarcolemma, spherical or ovoid subsarcolemmal mitochondria show accumulations. The mitochondria are numerous and large in size in the red fibers, intermediate in the intermediate fibers, and few and small in the white fibers. Paired, slender I-band-limited mitochondria were located on both sides of the Z-line and partly embraced the myofibrils at the I-band level; they occurred in all three types of fibers. In the intermyofibrillar spaces, numerous mitochondria formed mitochondrial columns. These columns were classified into two types: 1) thick mitochondrial columns, formed by multiple mitochondria each with an intermyofibrillar space corresponding to one sarcomere in length, and 2) thin mitochondrial columns, established by single mitochondria corresponding to one sarcomere in length. In the red fibers mitochondrial columns were abundant and the ratio of the thick and thin columns was almost the same, while in the intermediate fibers most of the columns belonged to the thin type. The white fibers displayed rare, very thin columns.
Insights
Mitochondrial structure varies across rat muscle fiber types. Red fibers have abundant, large mitochondria, while white fibers have few, small ones, impacting muscle energy.
Area of Science:
- Cell Biology
- Muscle Physiology
- Electron Microscopy
Background:
- Mitochondria are crucial for cellular energy production.
- Striated muscle fibers exhibit distinct metabolic and functional characteristics.
- Understanding mitochondrial arrangement is key to muscle function.
Purpose of the Study:
- To investigate the three-dimensional structure and arrangement of mitochondria in rat red, white, and intermediate striated muscle fibers.
- To correlate mitochondrial morphology and distribution with fiber type.
Main Methods:
- Field-emission scanning electron microscopy was employed.
- Cytoplasmic matrices were removed using the Osmium-DMSO-Osmium procedure.
- Detailed analysis of subsarcolemmal and intermyofibrillar mitochondria.
Main Results:
- Mitochondria quantity and size correlate with fiber type: abundant and large in red fibers, intermediate in intermediate fibers, and few and small in white fibers.
- Paired, slender mitochondria embrace myofibrils at the I-band level in all fiber types.
- Intermyofibrillar mitochondria form columns, classified as thick (multiple mitochondria) and thin (single mitochondria), with varying abundance and type ratios across fiber types.
Conclusions:
- Mitochondrial distribution and morphology are significantly different among rat striated muscle fiber types.
- These structural variations likely reflect functional adaptations related to energy metabolism in different muscle fibers.
- The study provides detailed insights into the ultrastructural organization of mitochondria in skeletal muscle.