Key result
Boa constrictor cardiac myofibers lack T-tubules and complex sarcoplasmic reticulum, featuring sarcolemma indentations and small vesicles.
Why the study?
The ultrastructural features of cardiac myofibers in the boa constrictor differ from other vertebrate cardiac and striated muscle cells and require detailed characterization.
The study identifies unique ultrastructural features in boa constrictor cardiac myofibers, notably the absence of a transverse tubular system, similar to slow or tonic muscle fibers.
No direct relevance to human cardiac physiology; extends comparative ultrastructure data but leaves functional implications open.
Electron microscopic observation of cardiac myofibers from the boa constrictor depict several features that differ from other vertebrate cardiac and striated muscle cells. The indentations in the sarcolemma do not penetrate into the deep sarcoplasmic matrix to form a transverse tubular system, instead the regular indentations extend the circumference of the myofiber at the regions of the Z line and are continuous with the latter via a dense homogeneous material that occurs at regular intervals along the subsarcolemmal surface. This dense material provides a direct contact between the sarcolemma and the contractile system. A complex sarcoplasmic reticulum was not observed around the myofibrils or in the sarcoplasmic matrix, instead there were small vesicles dispersed about the sarcoplasm. These myofibers are compared with the slow or tonic muscle fiber (Felderstruktur) which also lacks a transverse tubular system and contains an irregular sarcoplasmic reticulum.
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Lee V. Leak (1967) studied this question. Cardiac myofibers of the boa constrictor lack a transverse tubular system and complex sarcoplasmic reticulum, instead featuring regular sarcolemma indentations and dispersed small vesicles.
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