Affiliation:
1. From the Department of Physiology (B.A.C., M.R.L., D.P.F., R.L.M.), University of Wisconsin Medical School, Madison, Wis; and CSRRI and the Department of BCPS (T.B., T.C.I.), Illinois Institute of Technology, Chicago, Ill.
Abstract
Protein kinase A–mediated (PKA) phosphorylation of cardiac myosin binding protein C (cMyBP-C) accelerates the kinetics of cross-bridge cycling and may relieve the tether-like constraint of myosin heads imposed by cMyBP-C. We favor a mechanism in which cMyBP-C modulates cross-bridge cycling kinetics by regulating the proximity and interaction of myosin and actin. To test this idea, we used synchrotron low-angle x-ray diffraction to measure interthick filament lattice spacing and the equatorial intensity ratio, I
11
/I
10
, in skinned trabeculae isolated from wild-type and cMyBP-C null (cMyBP-C
−/−
) mice. In wild-type myocardium, PKA treatment appeared to result in radial or azimuthal displacement of cross-bridges away from the thick filaments as indicated by an increase (approximately 50%) in I
11
/I
10
(0.22±0.03 versus 0.33±0.03). Conversely, PKA treatment did not affect cross-bridge disposition in mice lacking cMyBP-C, because there was no difference in I
11
/I
10
between untreated and PKA-treated cMyBP-C
−/−
myocardium (0.40±0.06 versus 0.42±0.05). Although lattice spacing did not change after treatment in wild-type (45.68±0.84 nm versus 45.64±0.64 nm), treatment of cMyBP-C
−/−
myocardium increased lattice spacing (46.80±0.92 nm versus 49.61±0.59 nm). This result is consistent with the idea that the myofilament lattice expands after PKA phosphorylation of cardiac troponin I, and when present, cMyBP-C, may stabilize the lattice. These data support our hypothesis that tethering of cross-bridges by cMyBP-C is relieved by phosphorylation of PKA sites in cMyBP-C, thereby increasing the proximity of cross-bridges to actin and increasing the probability of interaction with actin on contraction.
Publisher
Ovid Technologies (Wolters Kluwer Health)
Subject
Cardiology and Cardiovascular Medicine,Physiology
Cited by
95 articles.
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