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Strain-dependent cross-bridge cycle for muscle. II. Steady-state behavior
1Max-Planck Institute for Molecular Physiology, Dortmund, Germany.
Biophysical Journal
|August 1, 1995
Summary
This study models muscle mechanics using a strain-dependent cross-bridge model. It predicts muscle properties under varying conditions, identifying key steps limiting muscle function and ATP consumption.
Area of Science:
- Muscle physiology
- Biophysics
- Skeletal muscle mechanics
Background:
- Understanding muscle contraction relies on cross-bridge cycling models.
- Muscle properties are influenced by biochemical states and mechanical strain.
Purpose of the Study:
- To quantitatively predict steady-state muscle properties using a strain-dependent cross-bridge model.
- To investigate the influence of phosphate and nucleotide levels on isometric muscle properties.
- To identify rate-limiting steps in muscle cross-bridge cycling under different mechanical conditions.
Main Methods:
- Development of a quantitative, strain-dependent cross-bridge model.
- Simulation of muscle isometric and shortening/extension behaviors.
- Analysis of the impact of varying ATP, ADP, and Pi levels on cross-bridge kinetics.
Main Results:
- The model accurately describes isometric properties, predicting rigor-like states at low ATP.
- Strain-blocked ADP release is identified as rate-limiting for isometric and slow shortening.
- Under rapid shortening, ATP hydrolysis on detached heads becomes rate-limiting.
- Forced detachment of cross-bridges is necessary to explain tension during rapid extension.
Conclusions:
- The proposed cross-bridge model successfully predicts muscle steady-state properties.
- Biochemical states and mechanical strain critically regulate cross-bridge cycling and muscle force generation.
- The model provides insights into the ATPase rate and its dependence on actin site availability and strain.