Role of Mechanical Stimulation in the Establishment and Maintenance of Muscle Cell Differentiation

This chapter discusses the role of mechanical stimulation in the establishment and maintenance of muscle cell differentiation. The striated tissues of the myocardium and axial skeleton are exquisitely sensitive to changes in mechanical load. In the heart, an acute increase in preload can act to augment cardiac output on a beat-to-beat time scale. In skeletal muscle, it serves to accelerate shortening velocity and increase contractile force. During early embryonic life, the developing cardiac myocyte displays a rounded, ovoid shape. Myofibrils are disseminated throughout the sarcoplasm and intercellular junctions are distributed at irregular intervals along the periphery of the cells. With continued development, the myocytes grow severalfold in size and begin to gradually elongate to assume a rod-like shape. The essential role which mechanical forces play in directing cardiac morphogenesis is readily apparent when an intact, developing heart is partially unloaded. Externally derived forces may also serve as an early signal that acts to direct the nucleation of myofibrils in the developing heart. Because the primitive myofibrils of the heart appear to be attached to the sarcolemma through nascent costameres and fascia adherens junctions, they appear to be subject to the extrinsic tensile forces that must accompany these morphogenetic events.