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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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Mechanical properties of activated muscle fibers.Magnitude of the complex modulus, phase, elastic modulus, and viscous modulus for activated muscle fibers during the final five oscillations of the driven oscillation. All data points are (MEAN±SEM), and the number of fibers analyzed was N = 8.
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pone.0121726.g006: Mechanical properties of activated muscle fibers.Magnitude of the complex modulus, phase, elastic modulus, and viscous modulus for activated muscle fibers during the final five oscillations of the driven oscillation. All data points are (MEAN±SEM), and the number of fibers analyzed was N = 8.

Mentions: For driving oscillations of 15 Hz or less, the last five oscillations of the force response were used to calculate the magnitude of the complex modulus and the viscous and elastic moduli of the fiber (Fig 6). Although there was a large variability in the magnitude of these values, the fibers exhibited the same general pattern. The response of the fiber was maximal at 1 Hz, where the elastic modulus of the fiber peaked, while the viscous modulus decreased with increasing frequency.


Thixotropy and rheopexy of muscle fibers probed using sinusoidal oscillations.

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

Mechanical properties of activated muscle fibers.Magnitude of the complex modulus, phase, elastic modulus, and viscous modulus for activated muscle fibers during the final five oscillations of the driven oscillation. 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.g006: Mechanical properties of activated muscle fibers.Magnitude of the complex modulus, phase, elastic modulus, and viscous modulus for activated muscle fibers during the final five oscillations of the driven oscillation. All data points are (MEAN±SEM), and the number of fibers analyzed was N = 8.
Mentions: For driving oscillations of 15 Hz or less, the last five oscillations of the force response were used to calculate the magnitude of the complex modulus and the viscous and elastic moduli of the fiber (Fig 6). Although there was a large variability in the magnitude of these values, the fibers exhibited the same general pattern. The response of the fiber was maximal at 1 Hz, where the elastic modulus of the fiber peaked, while the viscous modulus decreased with increasing frequency.

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