The structural and functional effects of myosin regulatory light chain phosphorylation are amplified by increases in sarcomere length and [Ca2+]

figure legend Increases in [Ca2+] (yellow circles), sarcomere length (SL) and phosphorylation of regulatory light chain (RLC-P; blue circles) all contribute to increases in myocardial contractility. We investigated the role of RLC-P on cardiac structure and function while [Ca2+] and SL were altered. Increasing [Ca2+], SL and RLC-P increased disorder of the myosin heads along the thick filament, which led to increased isometric stress, greater viscoelastic myocardial stiffness, and prolong cross-bridge attachment due to slowed ADP release from strongly bound myosin heads. These findings demonstrate a progressive pathway of myofilament activation whereby increases in RLC-P amplify force production due to increases in [Ca2+] and SL. image