Abstract 16507: Frequency Dependent Phosphorylation of Cardiac Myosin Binding Protein-C Mediates Acceleration of Myocardial Relaxation to Support Normal Diastolic Function
Cardiac myosin binding protein-C (cMyBP-C), a phosphorylatable thick filament accessory protein, may act as an inhibitory regulator of cross-bridge cycling. We propose that frequency dependent phosphorylation of cMyBP-C ameliorates its inhibition of cycling to accelerate myocardial relaxation in support of normal diastolic function. To test this hypothesis, we used previously developed transgenic mice of cMyBP-C null background to express either wild type cMyBP-C (tWT) or non-phosphorlylatable mutant cMyBP-C with ser to ala substitutions at 3 known phosphorylation sites (t3SA) on cMyBP-C. Echocardiogram results showing similar ejection fraction, increased isovolumetric relaxation time, and increased mitral inflow/tissue Doppler ratio indicated that t3SA hearts to have predominantly diastolic dysfunction. Interestingly, t3SA hearts also showed depressed myocardial maximum relaxation/contraction velocity ratio (Ea/Sa). Using |(-dF/dt)max/(+dF/dt)max| on paced intact papillary muscle as an index of relaxation analogous to Es/Sa, t3SA myocardium was found to be unable to accelerate relaxation when pacing frequency was increased from 1 to 3 Hz, unlike tWT. This lack of frequency dependent acceleration of relaxation in t3SA myocardium occurred despite similar frequency dependent acceleration of the [Ca2+] decay. Site-specific anti-phosphoserine antibodies only detected Ser-302 to be phosphorylated in explanted and paced tWT hearts in Langendorff perfusion. Recombinant calcium-calmodulin kinase 2δ (CaMK2δ), which is a calcium transient frequency activated kinase expressed in the heart, preferentially phosphorylated Ser-302 on WT recombinant cMyBP-C in solution. Thus, frequency dependent phosphorylation of cMyBP-C by CaMK2δ on Ser-302 promotes acceleration of myocardial relaxation in support of normal diastolic function.
- © 2010 by American Heart Association, Inc.