The study demonstrates the existence of a previously undetected radial component of force generated by cycling crossbridges in muscle fibers, showing that the myofilament lattice does not maintain a constant volume during force changes.
Reveals radial crossbridge forces in vitro; extends sarcomere mechanics models but leaves in vivo cardiac relevance open.
Time-resolved lattice spacing changes were measured (10-millisecond time resolution) by x-ray diffraction of synchrotron radiation in single intact muscle fibers of the frog Rana temporaria undergoing electrically stimulated tension development during application of stretches and releases. Ramp releases, which decreased fiber length at constant speed, caused a lattice expansion. After the ramp, increasing tension during recovery was accompanied by lattice compression. Ramp stretches caused a compression of the lattice. While the fiber was held at a constant length after the stretch, tension decreased and lattice spacing increased. These observations demonstrate the existence of a previously undetected radial component of the force generated by a cycling crossbridge. At sarcomere lengths of 2.05 to 2.2 micrometers, the radial force compresses the myofilament lattice. Hence, the myofilament lattice does not maintain a constant volume during changes in force.
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Cecchi et al. (1990) studied this question.
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