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Thixotropy and rheopexy of muscle fibers probed using sinusoidal oscillations.

Altman D, Minozzo FC, Rassier DE - PLoS ONE (2015)

Bottom Line: Length changes of muscle fibers have previously been shown to result in a temporary reduction in fiber stiffness that is referred to as thixotropy.Treatment of these fibers with EDTA and blebbistatin, which inhibits myosin-actin interactions, quashed this effect, suggesting that the mechanism of muscle fiber thixotropy is cross-bridge dependent.Blebbistatin and EDTA did not disrupt the rheopectic behavior, suggesting that a non-cross-bridge mechanism contributes to this phenomenon.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, Willamette University, Salem, Oregon, United States of America.

ABSTRACT
Length changes of muscle fibers have previously been shown to result in a temporary reduction in fiber stiffness that is referred to as thixotropy. Understanding the mechanism of this thixotropy is important to our understanding of muscle function since there are many instances in which muscle is subjected to repeated patterns of lengthening and shortening. By applying sinusoidal length changes to one end of single permeabilized muscle fibers and measuring the force response at the opposite end, we studied the history-dependent stiffness of both relaxed and activated muscle fibers. For length change oscillations greater than 1 Hz, we observed thixotropic behavior of activated fibers. Treatment of these fibers with EDTA and blebbistatin, which inhibits myosin-actin interactions, quashed this effect, suggesting that the mechanism of muscle fiber thixotropy is cross-bridge dependent. We modeled a half-sarcomere experiencing sinusoidal length changes, and our simulations suggest that thixotropy could arise from force-dependent cross-bridge kinetics. Surprisingly, we also observed that, for length change oscillations less than 1 Hz, the muscle fiber exhibited rheopexy. In other words, the stiffness of the fiber increased in response to the length changes. Blebbistatin and EDTA did not disrupt the rheopectic behavior, suggesting that a non-cross-bridge mechanism contributes to this phenomenon.

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Changing force response for a simulated half-sarcomere.The root-mean-squared (RMS) amplitude for the initial driving oscillation (a) and the final driving oscillation (b) for a simulated half-sarcomere. (c) The ratio of the initial and final RMS amplitudes for a simulated half-sarcomere. The total length of the oscillation was 2 seconds.
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pone.0121726.g011: Changing force response for a simulated half-sarcomere.The root-mean-squared (RMS) amplitude for the initial driving oscillation (a) and the final driving oscillation (b) for a simulated half-sarcomere. (c) The ratio of the initial and final RMS amplitudes for a simulated half-sarcomere. The total length of the oscillation was 2 seconds.

Mentions: In addition, we calculated the RMS amplitude of the first oscillation (Fig 11A) and last oscillation (Fig 11B) for each simulated force trace, and plotted the ratio of these amplitudes as a function of frequency (Fig 11C). Consistent with our data, the magnitude of the thixotropic effect was greater at higher frequencies. Also consistent with our data, the thixotropic effect arises primarily because of an increase in the initial RMS amplitude, with the final RMS amplitude remaining fairly constant as the frequency is varied.


Thixotropy and rheopexy of muscle fibers probed using sinusoidal oscillations.

Altman D, Minozzo FC, Rassier DE - PLoS ONE (2015)

Changing force response for a simulated half-sarcomere.The root-mean-squared (RMS) amplitude for the initial driving oscillation (a) and the final driving oscillation (b) for a simulated half-sarcomere. (c) The ratio of the initial and final RMS amplitudes for a simulated half-sarcomere. The total length of the oscillation was 2 seconds.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4400131&req=5

pone.0121726.g011: Changing force response for a simulated half-sarcomere.The root-mean-squared (RMS) amplitude for the initial driving oscillation (a) and the final driving oscillation (b) for a simulated half-sarcomere. (c) The ratio of the initial and final RMS amplitudes for a simulated half-sarcomere. The total length of the oscillation was 2 seconds.
Mentions: In addition, we calculated the RMS amplitude of the first oscillation (Fig 11A) and last oscillation (Fig 11B) for each simulated force trace, and plotted the ratio of these amplitudes as a function of frequency (Fig 11C). Consistent with our data, the magnitude of the thixotropic effect was greater at higher frequencies. Also consistent with our data, the thixotropic effect arises primarily because of an increase in the initial RMS amplitude, with the final RMS amplitude remaining fairly constant as the frequency is varied.

Bottom Line: Length changes of muscle fibers have previously been shown to result in a temporary reduction in fiber stiffness that is referred to as thixotropy.Treatment of these fibers with EDTA and blebbistatin, which inhibits myosin-actin interactions, quashed this effect, suggesting that the mechanism of muscle fiber thixotropy is cross-bridge dependent.Blebbistatin and EDTA did not disrupt the rheopectic behavior, suggesting that a non-cross-bridge mechanism contributes to this phenomenon.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, Willamette University, Salem, Oregon, United States of America.

ABSTRACT
Length changes of muscle fibers have previously been shown to result in a temporary reduction in fiber stiffness that is referred to as thixotropy. Understanding the mechanism of this thixotropy is important to our understanding of muscle function since there are many instances in which muscle is subjected to repeated patterns of lengthening and shortening. By applying sinusoidal length changes to one end of single permeabilized muscle fibers and measuring the force response at the opposite end, we studied the history-dependent stiffness of both relaxed and activated muscle fibers. For length change oscillations greater than 1 Hz, we observed thixotropic behavior of activated fibers. Treatment of these fibers with EDTA and blebbistatin, which inhibits myosin-actin interactions, quashed this effect, suggesting that the mechanism of muscle fiber thixotropy is cross-bridge dependent. We modeled a half-sarcomere experiencing sinusoidal length changes, and our simulations suggest that thixotropy could arise from force-dependent cross-bridge kinetics. Surprisingly, we also observed that, for length change oscillations less than 1 Hz, the muscle fiber exhibited rheopexy. In other words, the stiffness of the fiber increased in response to the length changes. Blebbistatin and EDTA did not disrupt the rheopectic behavior, suggesting that a non-cross-bridge mechanism contributes to this phenomenon.

Show MeSH
Related in: MedlinePlus