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MUSCLE AND CONTRACTILITY |
1 ETH Zurich
2 University of Cologne
* To whom correspondence should be addressed. E-mail: robert.stehle{at}uni-koeln.de.
Submitted on July 8, 2005
Revised on August 14, 2005
Accepted on 19 September 2005
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Abstract |
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-actinin or myomesin, and a secondary fluorescently labeled Fab-fragment. We simultaneously measured force kinetics and determined the positions of the Z-line and M-band signals by fluorescence video microscopy and sophisticated computer vision (tracking) algorithms. Upon calcium activation, sarcomeres and half-sarcomeres shortened non-uniformly. Shortening occurred first rapidly and exponentially during the force rise, and then slowly during the force plateau. In psoas myofibrils, time-resolved displacements of the A-band in sarcomeres were observed i.e., the two halves of individual sarcomeres behaved non-uniformly. Non-uniformity in length changes between the two halves of sarcomeres was comparable to that between two adjacent half-sarcomeres of neighboring sarcomeres. Sequential lengthening of half-sarcomeres was observed in cardiac myofibrils during the rapid phase of force relaxation. The independent dynamics of the halves in a sarcomere reveals rather the half-sarcomere as the functional unit than the structural unit, the sarcomere. The technique will facilitate the study of filament sliding within individual half-sarcomeres and the mechanics of intersegmental chemomechanical coupling in multi-segmental striated muscles.
Key Words: cross-bridge kinetics, fluorescent video microscopy, half-sarcomere, non-uniformity, sarcomere length, titin
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