Filament compliance effects can explain tension overshoots
during force development
Kenneth S Campbell 1*
1 University of Kentucky
* To whom correspondence should be addressed. E-mail: k.s.campbell{at}uky.edu.
Submitted on April 15, 2006
Revised on May 30, 2006
Accepted on 22 August 2006
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Abstract |
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Spatially explicit stochastic simulations of myosin S1 heads attaching to a single actin filament were used to investigate the process of force development in contracting muscle. Filament compliance effects were incorporated by adjusting the spacing between adjacent actin binding sites and adjacent myosin heads in response to cross-bridge attachment/detachment events. Appropriate model parameters were determined by multidimensional optimization and used to simulate force development records corresponding to different levels of Ca2+ activation. Simulations in which the spacing between both adjacent actin binding sites and adjacent myosin S1 heads changed by ~0.06 nm following cross-bridge attachment/detachment events (1) exhibited tension overshoots with a similar Ca2+ dependence to that measured experimentally (Campbell 2006. Biophys J. 90:1288-1294) and (2) mimicked the observed ktr - relative tension relationship without invoking a Ca2+-dependent increase in the rate of cross-bridge state transitions. Tension did not overshoot its steady-state value in control simulations modeling rigid thick and thin filaments with otherwise identical parameters. These results underline the importance of filament geometry and actin binding site availability in quantitative theories of muscle contraction.
Key Words:
acto-myosin interactions, cross-bridge, muscle mechanics
