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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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Length change and force response of a muscle fiber experiencing driving sinusoidal oscillations.Length changes are shown in black, and the force response is in red. The mean force and length have been subtracted from the traces. 0.25 Hz oscillations of (a) the relaxed fiber, (b) the activated fiber, and (c) the activated fiber following treatment with EDTA and blebbistatin. 10 Hz oscillation of (d) the relaxed fiber, (e) the activated fiber, and (f) the activated fiber following treatment with EDTA and blebbistatin. The length of the fiber was 2.6 mm.
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pone.0121726.g001: Length change and force response of a muscle fiber experiencing driving sinusoidal oscillations.Length changes are shown in black, and the force response is in red. The mean force and length have been subtracted from the traces. 0.25 Hz oscillations of (a) the relaxed fiber, (b) the activated fiber, and (c) the activated fiber following treatment with EDTA and blebbistatin. 10 Hz oscillation of (d) the relaxed fiber, (e) the activated fiber, and (f) the activated fiber following treatment with EDTA and blebbistatin. The length of the fiber was 2.6 mm.

Mentions: Individual muscle fibers were subjected to sinusoidal length changes at one end at frequencies ranging from 0.25 to 30 Hz, and the resulting force response was measured at the other end of the fiber. Examples of length and force time traces at different experimental conditions are shown in Fig 1.


Thixotropy and rheopexy of muscle fibers probed using sinusoidal oscillations.

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

Length change and force response of a muscle fiber experiencing driving sinusoidal oscillations.Length changes are shown in black, and the force response is in red. The mean force and length have been subtracted from the traces. 0.25 Hz oscillations of (a) the relaxed fiber, (b) the activated fiber, and (c) the activated fiber following treatment with EDTA and blebbistatin. 10 Hz oscillation of (d) the relaxed fiber, (e) the activated fiber, and (f) the activated fiber following treatment with EDTA and blebbistatin. The length of the fiber was 2.6 mm.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0121726.g001: Length change and force response of a muscle fiber experiencing driving sinusoidal oscillations.Length changes are shown in black, and the force response is in red. The mean force and length have been subtracted from the traces. 0.25 Hz oscillations of (a) the relaxed fiber, (b) the activated fiber, and (c) the activated fiber following treatment with EDTA and blebbistatin. 10 Hz oscillation of (d) the relaxed fiber, (e) the activated fiber, and (f) the activated fiber following treatment with EDTA and blebbistatin. The length of the fiber was 2.6 mm.
Mentions: Individual muscle fibers were subjected to sinusoidal length changes at one end at frequencies ranging from 0.25 to 30 Hz, and the resulting force response was measured at the other end of the fiber. Examples of length and force time traces at different experimental conditions are shown in Fig 1.

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