Abstract
The longitudinal and transverse stiffness of myofibrils of rabbit skeletal muscle were examined under various physiological conditions to study the mechanical characteristics of the sarcomere structures of skeletal muscle fibers. Myofibrils were prepared from glycerinated fibers of rabbit psoas muscle. The longitudinal stiffness was examined for single myofibrils suspended between micro-needles based on the force responses of myofibrils to sinusoidal length changes. The transverse stiffness was examined for single myofibrils immobilized to the surface of aminosilane-treated coverslip based on force-distance curves obtained for the overlap regions of myofibrils by use of an atomic force microscope (AFM). By assuming that myofibrils are uniform rods, their Young's modulus was estimated. The Young's modulus of myofibrils was about 200-times greater in the longitudinal direction than in the transverse direction under various physiological conditions. The magnitudes of the longitudinal and transverse Young's modulus of myofibrils thus obtained linearly changed by changing the physiological conditions. The results obtained suggest that the overall mechanical strength of myofibrils is almost exclusively determined by the actomyosin filament networks linked by attached cross-bridges and that the mechanical anisotropy of myofibrils comes from the anisotropic nature of the actomyosin filament networks thus produced in the sarcomere structures. [J Physiol Sci. 2007;57 Suppl:S97]
