cMyBP-C phosphorylation modulates the time-dependent slowing of unloaded shortening in murine skinned myocardium

• Published in: The Journal of general physiology Vol. 153; no. 3; p. 1
• Main Authors: Giles, Jasmine, Fitzsimons, Daniel P, Patel, Jitandrakumar R, Knudtsen, Chloe, Neuville, Alexander, Moss, Richard L
• Format: Journal Article
• Language: English
• Published: United States Rockefeller University Press 01-03-2021
• Subjects: Actin; Animals; Calcium; Cardiac muscle; Carrier Proteins - metabolism; Contraction and cell motility; Kinases; Mice; Mice, Knockout; Myocardial Contraction; Myocardium; Myocardium - metabolism; Myofilament Special Issue, 2020; Myosin; Phosphorylation; Protein kinase A; Protein structure and dynamics; Velocity
• ISSN: 0022-1295; 1540-7748
• DOI: 10.1085/jgp.202012782

In myocardium, phosphorylation of cardiac myosin-binding protein-C (cMyBP-C) is thought to modulate the cooperative activation of the thin filament by binding to myosin and/or actin, thereby regulating the probability of cross-bridge binding to actin. At low levels of Ca2+ activation, unloaded shortening velocity (Vo) in permeabilized cardiac muscle is comprised of an initial high-velocity phase and a subsequent low-velocity phase. The velocities in these phases scale with the level of activation, culminating in a single high-velocity phase (Vmax) at saturating Ca2+. To test the idea that cMyBP-C phosphorylation contributes to the activation dependence of Vo, we measured Vo before and following treatment with protein kinase A (PKA) in skinned trabecula isolated from mice expressing either wild-type cMyBP-C (tWT), nonphosphorylatable cMyBP-C (t3SA), or phosphomimetic cMyBP-C (t3SD). During maximal Ca2+ activation, Vmax was monophasic and not significantly different between the three groups. Although biphasic shortening was observed in all three groups at half-maximal activation under control conditions, the high- and low-velocity phases were faster in the t3SD myocardium compared with values obtained in either tWT or t3SA myocardium. Treatment with PKA significantly accelerated both the high- and low-velocity phases in tWT myocardium but had no effect on Vo in either the t3SD or t3SA myocardium. These results can be explained in terms of a model in which the level of cMyBP-C phosphorylation modulates the extent and rate of cooperative spread of myosin binding to actin.