Cooperative activation of the cardiac myofilament: the pivotal role of tropomyosin.

The contraction and relaxation of the beating heart are mediated by highly coordinated processes that allow rapid activation and deactivation of the myofilaments. The sarcomere is the fundamental contractile element, and its shortening is the result of the myosin-containing thick filament sliding past the actin-containing thin filament. Fueled by ATP hydrolysis, myosin is the molecular motor that drives sarcomere shortening through a cyclic, ratchet-like interaction with actin. A critical component of cardiac contraction is the regulation of myosin-actin interactions, which are governed predominantly by the thin-filament regulatory proteins troponin and tropomyosin.