Published online before print March 30, 2006, doi: 10.1161/01.RES.0000219863.94390.ce
© 2006 American Heart Association, Inc.
Integrative Physiology |
Ablation of Cardiac Myosin-Binding Protein-C Accelerates Stretch Activation in Murine Skinned Myocardium
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, 601 Science Dr, Madison, WI 53711. E-mail stelzer{at}physiology.wisc.edu
Cardiac myosin binding protein-C (cMyBP-C) is a thick filament accessory protein that binds tightly to myosin, but despite evidence that mutations in the cMyBP-C gene comprise a frequent cause of hypertrophic cardiomyopathy, relatively little is known about the role(s) of cMyBP-C in myocardium. Based on earlier studies demonstrating the potential importance of stretch activation in cardiac contraction, we examined the effects of cMyBP-C on the stretch activation responses of skinned ventricular preparations from wild-type (WT) and homozygous cMyBP-C knockout mice (cMyBP-C–/–) previously developed in our laboratory. Sudden stretch of skinned myocardium during maximal or submaximal Ca2+ activations resulted in an instantaneous increase in force that quickly decayed to a minimum and was followed by a delayed redevelopment of force (ie, stretch activation) to levels greater than prestretch force. Ablation of cMyBP-C dramatically altered the stretch activation response, ie, the rates of force decay and delayed force transient were accelerated compared with WT myocardium. These results suggest that cMyBP-C normally constrains the spatial position of myosin cross-bridges, which, in turn, limits both the rate and extent of interaction of cross-bridges with actin. We propose that ablation of cMyBP-C removes this constraint, increases the likelihood of cross-bridge binding to actin, and speeds the rate of delayed force development following stretch. Regardless of the specific mechanism, acceleration of cross-bridge cycling in cMyBP-C–/– myocardium could account for the abbreviation of systolic ejection in this mouse as a direct consequence of premature stretch activation of ventricular myocardium.
Key Words: cross-bridge kinetics • cooperativity • contractile proteins • regulation of contraction
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