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Hypertrophic smooth muscle. II. Sarcoplasmic reticulum, caveolae and mitochondria
Abstract:
The cytological features of hypertrophic smooth muscle cells are investigated in the small intestine of the guinea pig in which a hypertrophy is induced by an experimental stenosis. By freeze-fracture the cell membrane appears richer in intramembrane particles than that of control muscle cells, whereas the number of caveolae per unit surface of cell membrane shows little or no change (16--19 caveolae micron-2). In the sarcoplasm there is a conspicuous increase of both smooth and rough sarcoplasmic reticulum; extent was measured by surface and by volume. Unusual forms of reticulum also appear. Mitochondria are reduced (in percentage volume) to about half the control value.
Insights
Hypertrophic smooth muscle cells in guinea pig small intestine show increased cell membranes and sarcoplasmic reticulum after experimental stenosis. Mitochondria volume decreased, while caveolae remained unchanged.
Area of Science:
- Cell Biology
- Gastrointestinal Physiology
- Smooth Muscle Research
Background:
- Smooth muscle hypertrophy is a significant adaptation in various physiological and pathological conditions.
- Understanding the ultrastructural changes in hypertrophic smooth muscle is crucial for comprehending its function.
Purpose of the Study:
- To investigate the cytological alterations in hypertrophic smooth muscle cells of the guinea pig small intestine induced by experimental stenosis.
- To characterize changes in cell membrane, sarcoplasmic reticulum, and mitochondria.
Main Methods:
- Experimental induction of smooth muscle hypertrophy via stenosis in guinea pig small intestine.
- Freeze-fracture electron microscopy to analyze cell membrane structure.
- Quantitative assessment of sarcoplasmic reticulum and mitochondria volume and surface area.
Main Results:
- Freeze-fracture revealed an increase in intramembrane particles in the cell membrane of hypertrophic cells compared to controls.
- The density of caveolae per unit surface area of the cell membrane remained largely unchanged.
- Significant increases in both smooth and rough sarcoplasmic reticulum were observed in terms of surface area and volume.
- Mitochondria volume was reduced by approximately 50% in hypertrophic cells relative to control cells.
- Unusual forms of sarcoplasmic reticulum were also noted.
Conclusions:
- Experimental stenosis induces significant ultrastructural modifications in small intestine smooth muscle cells.
- These changes include alterations in cell membrane composition, a substantial increase in sarcoplasmic reticulum, and a decrease in mitochondrial volume.
- The observed cytological adaptations likely contribute to the functional changes associated with smooth muscle hypertrophy.