Key result
Cardiac myofibrils show greater stiffness than skeletal myofibrils across rigor and relaxed states.
Why the study?
The transverse stiffness characteristics of single myofibrils from skeletal and cardiac muscles and their structural basis were not fully understood.
Cardiac myofibrils exhibit greater transverse stiffness than skeletal myofibrils, likely due to stronger sarcomere components such as Z-bands and titin networks.
Answers are grounded in this paper and cite their sources.
May inform cardiac vs skeletal muscle mechanics models; leaves open Z-band roles in human diastolic dysfunction.
The transverse stiffness of single myofibrils of skeletal and cardiac muscles was examined by atomic force microscopy. The microscopic images of both skeletal and cardiac myofibrils in a rigor state showed periodical striation patterns separated by Z-bands, which is characteristic of striated muscle fibers. However, sarcomere patterns were hardly distinguishable in the stiffness distributions of the relaxed myofibrils of skeletal and cardiac muscles. Myofibrils in a rigor state were significantly stiff compared with those in a relaxed state, and in each state, cardiac myofibrils were significantly stiffer compared with skeletal myofibrils. By proteolytic digestions of sarcomere components of myofibrils, it was suggested that cardiac myofibrils are laterally stiffer than skeletal myofibrils because Z-bands, connectin (titin) filament networks, and other components of sarcomere structures for the former myofibrils are stronger than those for the latter.
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Akiyama et al. (2007) studied this question. Cardiac myofibrils vs. Skeletal myofibrils was evaluated on Transverse stiffness. Cardiac myofibrils were significantly stiffer than skeletal myofibrils in both rigor and relaxed states, likely due to stronger Z-bands and connectin filament networks.
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