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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 activated muscle fibers.The root-mean-squared (RMS) amplitude for the initial driving oscillation (a) and the final driving oscillation (b) for activated muscle fibers. (c) The ratio of the initial and final RMS amplitudes for activated muscle fibers. The total length of the oscillation was 20 seconds. All data points are (MEAN±SEM), and the number of fibers analyzed was N = 8.
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pone.0121726.g005: Changing force response for activated muscle fibers.The root-mean-squared (RMS) amplitude for the initial driving oscillation (a) and the final driving oscillation (b) for activated muscle fibers. (c) The ratio of the initial and final RMS amplitudes for activated muscle fibers. The total length of the oscillation was 20 seconds. All data points are (MEAN±SEM), and the number of fibers analyzed was N = 8.

Mentions: To quantify this effect, we again calculated the RMS amplitude of each force time trace’s first oscillation (Fig 5A) and last oscillation (Fig 5B), and we calculated the ratio of these amplitudes (Fig 5C). Below 1 Hz, this ratio is less than 1, indicating the fiber is growing stiffer over time. Above 1 Hz, the ratio is greater than 1, indicating that the fiber is softening. Furthermore, the ratio gets larger as the driving frequency is increased.


Thixotropy and rheopexy of muscle fibers probed using sinusoidal oscillations.

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

Changing force response for activated muscle fibers.The root-mean-squared (RMS) amplitude for the initial driving oscillation (a) and the final driving oscillation (b) for activated muscle fibers. (c) The ratio of the initial and final RMS amplitudes for activated muscle fibers. The total length of the oscillation was 20 seconds. All data points are (MEAN±SEM), and the number of fibers analyzed was N = 8.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0121726.g005: Changing force response for activated muscle fibers.The root-mean-squared (RMS) amplitude for the initial driving oscillation (a) and the final driving oscillation (b) for activated muscle fibers. (c) The ratio of the initial and final RMS amplitudes for activated muscle fibers. The total length of the oscillation was 20 seconds. All data points are (MEAN±SEM), and the number of fibers analyzed was N = 8.
Mentions: To quantify this effect, we again calculated the RMS amplitude of each force time trace’s first oscillation (Fig 5A) and last oscillation (Fig 5B), and we calculated the ratio of these amplitudes (Fig 5C). Below 1 Hz, this ratio is less than 1, indicating the fiber is growing stiffer over time. Above 1 Hz, the ratio is greater than 1, indicating that the fiber is softening. Furthermore, the ratio gets larger as the driving frequency is increased.

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