Differences in titin segmental elongation between passive and active stretch in skeletal muscle.

摘要: ABSTRACT Since the 1950s, muscle contraction has been explained using a two-filament system in which actin and myosin exclusively dictate active force sarcomeres. Decades later, third filament called titin was discovered. This recently identified as an important regulator of force, but yet to be incorporated into contemporary theories contraction. When sarcomeres are actively stretched, substantial rapid increase occurs, suggested arise part from titin–actin binding that is absent passively stretched However, there currently no direct evidence for such within Therefore, we aimed determine whether binds not by observing length changes proximal distal segments presence absence calcium. We labeled I-band with fluorescent F146 antibody rabbit psoas myofibrils tracked segmental elongations during passive (no calcium) (high stretch. Without calcium, elongated expected based on their free spring properties. In contrast, stretch differed statistically stretch, demonstrating calcium activation increases segment stiffness, actin-dependent manner. The consistent elongation contrary what if titin9s attached actin. calcium-dependent change stiffness likely contributes regulation addition myosin.