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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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Frequency components of the force signal for a muscle fiber experiencing sinusoidal oscillations.A Fourier transform was applied to the force measurement time-courses, and the powers of the signal at the fundamental frequency (which is the same as the driving frequency) and the next two harmonics were calculated. Plotted are the ratios of the power at the second or third harmonic (P) and the power at the fundamental frequency (Pf) for three different experimental conditions.
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pone.0121726.g002: Frequency components of the force signal for a muscle fiber experiencing sinusoidal oscillations.A Fourier transform was applied to the force measurement time-courses, and the powers of the signal at the fundamental frequency (which is the same as the driving frequency) and the next two harmonics were calculated. Plotted are the ratios of the power at the second or third harmonic (P) and the power at the fundamental frequency (Pf) for three different experimental conditions.

Mentions: If the muscle fiber were a linear viscoelastic material, the Lissajous figures would be ellipses. As can be seen, the plots are not ellipses, indicating a nonlinearity that becomes more pronounced at higher frequencies of oscillation. To characterize this, a Fourier transform was applied to the force time-traces, and the powers of the signal at the fundamental frequency (which is the same as the frequency of the length changes) and the next two harmonics were calculated. An example of this analysis is shown in Fig 2, where we have plotted the ratios of the power at the second or third harmonic (P) and the power at the fundamental frequency (Pf) for various experimental conditions. As can be seen, the non-linearity in the signal primarily arises from the second harmonic, and this component becomes larger as the driving frequency increases.


Thixotropy and rheopexy of muscle fibers probed using sinusoidal oscillations.

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

Frequency components of the force signal for a muscle fiber experiencing sinusoidal oscillations.A Fourier transform was applied to the force measurement time-courses, and the powers of the signal at the fundamental frequency (which is the same as the driving frequency) and the next two harmonics were calculated. Plotted are the ratios of the power at the second or third harmonic (P) and the power at the fundamental frequency (Pf) for three different experimental conditions.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0121726.g002: Frequency components of the force signal for a muscle fiber experiencing sinusoidal oscillations.A Fourier transform was applied to the force measurement time-courses, and the powers of the signal at the fundamental frequency (which is the same as the driving frequency) and the next two harmonics were calculated. Plotted are the ratios of the power at the second or third harmonic (P) and the power at the fundamental frequency (Pf) for three different experimental conditions.
Mentions: If the muscle fiber were a linear viscoelastic material, the Lissajous figures would be ellipses. As can be seen, the plots are not ellipses, indicating a nonlinearity that becomes more pronounced at higher frequencies of oscillation. To characterize this, a Fourier transform was applied to the force time-traces, and the powers of the signal at the fundamental frequency (which is the same as the frequency of the length changes) and the next two harmonics were calculated. An example of this analysis is shown in Fig 2, where we have plotted the ratios of the power at the second or third harmonic (P) and the power at the fundamental frequency (Pf) for various experimental conditions. As can be seen, the non-linearity in the signal primarily arises from the second harmonic, and this component becomes larger as the driving frequency increases.

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