Signaling in Cardiac Sarcomeres in Health and Disease
The cardiac muscle cell contains bundles of myofilaments that have distinct, repeating structures, termed sarcomeres, which represent the basic contractile units. The sarcomere is the region of myofilament structures between two Z-disks with interdigitating thick myosin and thin actin filaments. Cyclic elevations of intracellular Ca2+ concentrations with each heartbeat rapidly activate contraction and lead to myosin cross-bridges binding to actin filaments. Contraction occurs when myosin cross-bridges exert force on actin filaments with ATP hydrolysis. This force causes the thin filament to slide past the thick filament and allows the muscle to shorten and to develop force. Minireviews in this thematic series focus on the concept that an important aspect of regulation of the dynamics of the heartbeat is the prominent role played by mechanisms at the level of cardiac sarcomeric proteins.