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Beyond calcium: cross-bridge binding regulates titin's contribution to muscle force
Dhairya Desai1,2, Armaan Sekhon1,2, Chris Tiessen1,2
1Schulich School of Engineering, Department of Biomedical Engineering, University of Calgary, 2500 University Drive NW, Calgary, AB, Canada, T2N 1N4.
The Journal of Experimental Biology
|December 4, 2025
Summary
Muscle contraction involves actin and myosin, but titin
Area of Science:
- Muscle physiology
- Sarcomere mechanics
- Protein interactions
Background:
- Sliding filament and cross-bridge theories explain muscle contraction.
- These theories do not fully account for phenomena like residual force enhancement (rFE).
- The role of titin in active force and rFE is not well understood.
Purpose of the Study:
- To investigate the roles of calcium and cross-bridge formation in titin mechanics.
- To determine how titin's PEVK region is modulated during muscle contraction.
- To clarify titin's contribution to passive force and rFE.
Main Methods:
- Measuring the length of titin's PEVK region in sarcomeres.
- Experiments included passive stretch, active stretch with cross-bridge inhibition (BDM), and active isometric contraction.
- Utilizing BDM to inhibit cross-bridge formation.
Main Results:
- PEVK region lengths were similar during passive stretch and with cross-bridge inhibition.
- PEVK region lengths were significantly longer during active isometric contractions.
- Cross-bridge engagement, rather than calcium alone, affects titin's extensibility.
Conclusions:
- Cross-bridge engagement modulates titin extensibility and passive force.
- Titin's role in residual force enhancement is linked to cross-bridge interactions.
- This finding offers new insights into muscle mechanics beyond traditional theories.
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