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Updated: Jul 4, 2026
08:29
Assessment of Myofilament Ca2+ Sensitivity Underlying Cardiac Excitation-contraction Coupling
Published on: August 1, 2016
Millisecond time-resolved changes occurring in Ca2+-regulated myosin filaments upon relaxation
1Department of Cell Biology, University of Massachusetts Medical School, Worcester, MA 01655, USA.
Journal of Molecular Biology
|July 1, 2008
Summary
Muscle contraction involves myosin head movement. This study shows that myosin heads rapidly reorder during muscle relaxation, returning to ordered positions within 50 milliseconds.
Area of Science:
- Muscle physiology
- Biophysics
- Molecular biology
Background:
- Muscle contraction is initiated by calcium (Ca2+) binding or phosphorylation of myosin heads on thick filaments.
- In relaxed muscle, myosin heads are helically ordered, minimizing actin interaction.
- Upon Ca2+ binding, myosin heads become disordered, enabling actin interaction and contraction.
Purpose of the Study:
- To investigate the kinetics of myosin head reordering during muscle relaxation.
- To determine if the reordering process occurs on a physiologically relevant timescale.
Main Methods:
- Time-resolved negative staining electron microscopy.
- Analysis of Fourier transforms of electron microscopy images.
Main Results:
- Myosin heads regain axial ordering within 20 milliseconds after Ca2+ removal.
- Myosin heads achieve their final helical positions within 50 milliseconds.
- The rate of reordering is comparable to the rate of disordering during activation.
Conclusions:
- The rapid reordering of myosin heads is a critical component of muscle relaxation.
- Reformation of ordered structure and head-head interactions are essential for efficient muscle relaxation.
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