Key result
In single frog muscle fibres, stretch during isometric contraction increases half-sarcomere stiffness to a maximum of ~2 e(m0) for a distortion of ~6 nm, indicating rapid attachment of a second motor domain.
Stretch-induced sliding of the actin filament distorts the actin-attached motor domain of myosin dimers, providing steric conditions for rapid attachment of the second motor domain and explaining the resistance of active muscle to stretch.
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No direct clinical implications for cardiac muscle; leaves open whether second motor domain attachment occurs in mammalian myocardium.
Fusi et al. (2009) studied this question. Stretch during isometric tetanus vs. Rigor or isometric contraction without stretch was evaluated on Stiffness of the array of myosin motors in each half-sarcomere (e(m)). In single frog muscle fibres, stretch during isometric contraction increases half-sarcomere stiffness to a maximum of ~2 e(m0) for a distortion of ~6 nm, indicating rapid attachment of a second motor domain.
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