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(Circulation Research. 2006;99:884.)
© 2006 American Heart Association, Inc.

Integrative Physiology

Protein Kinase A–Mediated Acceleration of the Stretch Activation Response in Murine Skinned Myocardium Is Eliminated by Ablation of cMyBP-C

Julian E. Stelzer, Jitandrakumar R. Patel, Richard L. Moss

From the Department of Physiology, University of Wisconsin School of Medicine and Public Health, Madison.

Correspondence to Julian E. Stelzer, Department of Physiology, University of Wisconsin Medical School, 1300 University Ave, Madison, WI 53706. E-mail stelzer{at}physiology.wisc.edu

ß-Adrenergic agonists induce protein kinase A (PKA) phosphorylation of the cardiac myofilament proteins myosin binding protein C (cMyBP-C) and troponin I (cTnI), resulting in enhanced systolic function, but the relative contributions of cMyBP-C and cTnI to augmented contractility are not known. To investigate possible roles of cMyBP-C in this response, we examined the effects of PKA treatment on the rate of force redevelopment and the stretch activation response in skinned ventricular myocardium from both wild-type (WT) and cMyBP-C null (cMyBP-C^–/–) myocardium. In WT myocardium, PKA treatment accelerated the rate of force redevelopment and the stretch activation response, resulting in a shorter time to the peak of delayed force development when the muscle was stretched to a new isometric length. Ablation of cMyBP-C accelerated the rate of force redevelopment and stretch activation response to a degree similar to that observed in PKA treatment of WT myocardium; however, PKA treatment had no effect on the rate of force development and the stretch activation response in null myocardium. These results indicate that ablation of cMyBP-C and PKA treatment of WT myocardium have similar effects on cross-bridge cycling kinetics and suggest that PKA phosphorylation of cMyBP-C accelerates the rate of force generation and thereby contributes to the accelerated twitch kinetics observed in living myocardium during ß-adrenergic stimulation.

Key Words: cross-bridge kinetics • ß-adrenergic agonists • positive inotropy • contractile protein function

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