Transverse Stiffness of Myofibrils of Skeletal and Cardiac Muscles Studied by Atomic Force Microscopy

Abstract

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 rigor state showed periodical striation patterns separated by Z-bands, characteristic of striated muscle fibers. However sarcomere patterns were hardly distinguishable in the stiffness distributions of relaxed myofibrils of skeletal and cardiac muscles. Myofibrils in rigor state were significantly stiff compared with those in 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 as Z-bands,connectin (titin) filament networks, and other components of sarcomere structures for the former myofibrils are stronger than those for the latter.