
cMyBP-C phosphorylation modulates the time-dependent slowing of unloaded shortening in murine skinned myocardium
Author(s) -
Jasmine Giles,
Daniel P. Fitzsimons,
Jitandrakumar R. Patel,
Chloe Knudtsen,
Alexander Neuville,
Richard L. Moss
Publication year - 2021
Publication title -
the journal of general physiology/the journal of general physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.064
H-Index - 127
eISSN - 1540-7748
pISSN - 0022-1295
DOI - 10.1085/jgp.202012782
Subject(s) - phosphorylation , actin , myosin , biophysics , protein kinase a , cardiac muscle , chemistry , kinase , medicine , biology , microbiology and biotechnology , endocrinology
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.