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The cardiac ultrastructure of Chimaera monstrosa L. (Elasmobranchii: Holocephali)
Insights
This study details the heart
Area of Science:
- Cardiovascular Biology
- Comparative Anatomy
- Cellular Ultrastructure
Background:
- The heart's structure varies significantly across species.
- Understanding primitive vertebrate cardiac ultrastructure provides evolutionary insights.
Purpose of the Study:
- To describe the detailed ultrastructure of the heart in the cartilaginous fish, Chimaera monstrosa L.
- To identify unique cellular features and compare them across cardiac regions.
Main Methods:
- Transmission Electron Microscopy (TEM) was employed.
- Ultrastructural analysis of endocardial, epicardial, and myocardial cells was performed.
Main Results:
- Endocardial and epicardial cells exhibit similarities across cardiac regions.
- Myocardial cells display minor variations, with myofibers containing few myofibrils.
- Sarcomeres show a complete banding pattern (Z, A, I, M, N, H bands).
- Peripheral coupling-like structures are common, but T-tubules are absent.
- Epicardial cells are thicker with hexagonal surfaces and cytoplasmic extensions; endocardial cells are flat with large nuclei.
Conclusions:
- Chimaera monstrosa L. heart exhibits a distinct ultrastructure with specific adaptations.
- The poorly developed sarcoplasmic reticulum and absence of T-tubules suggest unique excitation-contraction coupling mechanisms.
- Comparison with other vertebrates highlights evolutionary divergence in cardiac muscle.
Abstract:
The ultrastructure of the heart in Chimaera monstrosa L. is described. The endocardial and the epicardial cells are similar in the three cardiac regions. Myocardial cells show small variations. The myofibred, 4--6 microns thick, contains one or a few myofibrils. Each myosin filament is surrounded by six actin filaments. The sarcomere banding pattern includes the Z-, A-, I-, M-, N-, and H-band. End-to-end attachments between myofibres are composed of alternating desmosomes and fasciae adhaerentes. Desmosomes and nexuses occur between longitudinally oriented cell surfaces. The sarcoplasmic reticulum is poorly developed but well defined. Peripheral coupling-like structures are common, T-tubules are absent. Membrane bound dense bodies occur in all regions. Areas with ribosomes and single myosin filaments are often seen. The epicardial cells have a regular hexagonal surface and are much thicker than the endocardial cells. Numerous short and few longer cytoplasmic extensions face the pericardial cavity. The flat endocardial cells contain a large nucleus and small amounts of cytoplasm.