Myofilamente

Myofilamente is a term used in some languages to denote the contractile filaments that form the core of muscle tissue, typically referring to the myofilament system within muscle fibers. In most English-language texts this system is described as myofilaments, consisting primarily of actin-containing thin filaments and myosin-containing thick filaments, together with various regulatory and structural proteins.

Structurally, thin filaments are composed of actin (F-actin) strands, along with regulatory proteins such as tropomyosin and the troponin complex, which control access to actin binding sites. Thick filaments are built from myosin II molecules with protruding heads that form cross-bridges with actin during contraction. Other proteins, including titin and nebulin, help organize filament length and provide elasticity and alignment within the sarcomere, the basic contractile unit of a muscle fiber.

Functionally, the interaction between myosin heads and actin drives the sliding of filaments past one another, shortening the sarcomere and causing muscle contraction. This process is regulated by calcium ions via the troponin-tropomyosin complex in skeletal and cardiac muscle, with ATP hydrolysis powering the cross-bridge cycle. In smooth muscle, contraction is regulated differently, often through calmodulin and myosin light-chain kinase, and filament arrangement is less strictly striped than in striated muscle.

Clinical relevance includes a range of myopathies and cardiomyopathies arising from defects in myofilament proteins. The concept of the myofilament system has its roots in the sliding filament theory developed in the mid-20th century.