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Ultrastructural study on the extrusion of multivesicular bodies from cardiac cells
Abstract:
Cardiac conducting fibers taken from 12 dogs were studied in the electron microscope. The majority of samples contained a moderate number of multivesicular bodies (MVB's) and an extremely high number occurred in one dog. Single MVB's were found in the perinuclear region and in the cytoplasm separating myofibrils. A high accumulation of MVB's occurred at the cell periphery within cytoplasmic stalks extending into the extracellular space, in the intercalated disc, and also outside of the cell. The latter appeared to be extruded from the cell in the following way: 1) peripheral cytoplasm formed stalk-like extensions which contained MVB's; 2) the stalks detached from the cell; 3) vacuolar and sarcolemmal membranes surrounding the MVB disintegrated; 4) vesicles released from MVB adhered to the cellular surface and the coat of their membrane blended with the coat of the sarcolemma. The above pattern seems to be the same in those parts of sarcolemma which face the interstitial tissue and in the intercalated disc.
Insights
Cardiac conducting fibers showed numerous multivesicular bodies (MVBs). These MVBs were observed accumulating at cell peripheries and extracellularly, suggesting a novel extrusion mechanism in canine cardiac cells.
Area of Science:
- Cardiology
- Cell Biology
- Histology
Background:
- Cardiac conducting fibers are crucial for coordinated heartbeats.
- The ultrastructure of these fibers, particularly concerning cellular components like multivesicular bodies (MVBs), is not fully understood.
Purpose of the Study:
- To investigate the presence and distribution of multivesicular bodies (MVBs) in canine cardiac conducting fibers.
- To elucidate the potential role and mechanism of MVB extrusion from cardiac conducting cells.
Main Methods:
- Electron microscopy was used to examine cardiac conducting fibers from 12 dogs.
- Detailed ultrastructural analysis focused on the location and morphology of MVBs.
Main Results:
- A moderate number of MVBs were found in most samples, with one dog exhibiting an extremely high quantity.
- MVBs were observed in perinuclear regions, between myofibrils, at the cell periphery, in cytoplasmic stalks, within the intercalated disc, and extracellularly.
- A mechanism for MVB extrusion involving stalk formation, detachment, membrane disintegration, and vesicle fusion with the sarcolemma was described.
Conclusions:
- Canine cardiac conducting fibers contain MVBs, with significant accumulation observed at the cell periphery and extracellularly.
- A novel pathway for MVB extrusion from cardiac conducting cells into the extracellular space and intercalated discs is proposed.
- These findings may offer new insights into intercellular communication or cellular maintenance within the cardiac conduction system.