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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 relaxed muscle fibers.The ratio of the initial and final RMS amplitudes for relaxed 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 = 6. A one-sample t-test was used to test the  hypothesis that data collected at each frequency comes from a normal distribution with mean equal to 1. For data points marked with an asterisk, the  hypothesis was rejected (p<0.05).
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pone.0121726.g003: Changing force response for relaxed muscle fibers.The ratio of the initial and final RMS amplitudes for relaxed 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 = 6. A one-sample t-test was used to test the hypothesis that data collected at each frequency comes from a normal distribution with mean equal to 1. For data points marked with an asterisk, the hypothesis was rejected (p<0.05).

Mentions: The force response of relaxed fibers does not appear to change significantly over time (Fig 1). To quantify this behavior, we calculated the root-mean-squared (RMS) amplitude of both the first force oscillation and the final force oscillation after twenty seconds. The ratio of these two values is plotted as a function of driving frequency in Fig 3. While these data suggest that there may be a slight decrease in the stiffness of the fiber over time, the ratio is statistically indistinguishable from 1 at most driving frequencies, indicating that the amplitude is similar at the beginning and end of the driving oscillation.


Thixotropy and rheopexy of muscle fibers probed using sinusoidal oscillations.

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

Changing force response for relaxed muscle fibers.The ratio of the initial and final RMS amplitudes for relaxed 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 = 6. A one-sample t-test was used to test the  hypothesis that data collected at each frequency comes from a normal distribution with mean equal to 1. For data points marked with an asterisk, the  hypothesis was rejected (p<0.05).
© Copyright Policy
Related In: Results  -  Collection

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

pone.0121726.g003: Changing force response for relaxed muscle fibers.The ratio of the initial and final RMS amplitudes for relaxed 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 = 6. A one-sample t-test was used to test the hypothesis that data collected at each frequency comes from a normal distribution with mean equal to 1. For data points marked with an asterisk, the hypothesis was rejected (p<0.05).
Mentions: The force response of relaxed fibers does not appear to change significantly over time (Fig 1). To quantify this behavior, we calculated the root-mean-squared (RMS) amplitude of both the first force oscillation and the final force oscillation after twenty seconds. The ratio of these two values is plotted as a function of driving frequency in Fig 3. While these data suggest that there may be a slight decrease in the stiffness of the fiber over time, the ratio is statistically indistinguishable from 1 at most driving frequencies, indicating that the amplitude is similar at the beginning and end of the driving oscillation.

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