Phosphorylation of cMyBP-C modulates the activation-dependence of unloaded shortening velocity at low levels of Ca2+ activation

Background: At low levels of Ca2+ activation, unloaded shortening velocity (Vo) in cardiac muscle is comprised of an initial high-velocity phase and a subsequent low-velocity phase. The velocities in both the fast and slow phases are known to scale with the level of activation, culminating in a single high-velocity phase at saturating Ca2+ (i.e., Vmax).