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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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Model of the half-sarcomere.(a) Individual cross-bridges are linearly elastic elements that pass through three states: two attached states (A1 and A2) and a detached state (D). The transition from A2 to D is irreversible, and the transition from A1 to A2 corresponds to the powerstroke. (b) Model of the half-sarcomere. The half-sarcomere was modeled as a cross-bridge element (CE), consisting of cross-bridges attached in parallel, which is in series with the series element (SE), which represents the myofilament compliance.
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pone.0121726.g009: Model of the half-sarcomere.(a) Individual cross-bridges are linearly elastic elements that pass through three states: two attached states (A1 and A2) and a detached state (D). The transition from A2 to D is irreversible, and the transition from A1 to A2 corresponds to the powerstroke. (b) Model of the half-sarcomere. The half-sarcomere was modeled as a cross-bridge element (CE), consisting of cross-bridges attached in parallel, which is in series with the series element (SE), which represents the myofilament compliance.

Mentions: A model of a half-sarcomere was developed that is based on the framework of Campbell and Moss [4, 27]. According to this model, a single myosin cycles through three-states: D (detached), A1 (first attached), and A2 (second attached) (Fig 9A). The transition between A1 and A2 corresponds to the powerstroke, and results in an increase in the length of the cross-bridge attachment of xps. The cross-bridge is modeled as a linear elastic element with stiffness κcb.


Thixotropy and rheopexy of muscle fibers probed using sinusoidal oscillations.

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

Model of the half-sarcomere.(a) Individual cross-bridges are linearly elastic elements that pass through three states: two attached states (A1 and A2) and a detached state (D). The transition from A2 to D is irreversible, and the transition from A1 to A2 corresponds to the powerstroke. (b) Model of the half-sarcomere. The half-sarcomere was modeled as a cross-bridge element (CE), consisting of cross-bridges attached in parallel, which is in series with the series element (SE), which represents the myofilament compliance.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0121726.g009: Model of the half-sarcomere.(a) Individual cross-bridges are linearly elastic elements that pass through three states: two attached states (A1 and A2) and a detached state (D). The transition from A2 to D is irreversible, and the transition from A1 to A2 corresponds to the powerstroke. (b) Model of the half-sarcomere. The half-sarcomere was modeled as a cross-bridge element (CE), consisting of cross-bridges attached in parallel, which is in series with the series element (SE), which represents the myofilament compliance.
Mentions: A model of a half-sarcomere was developed that is based on the framework of Campbell and Moss [4, 27]. According to this model, a single myosin cycles through three-states: D (detached), A1 (first attached), and A2 (second attached) (Fig 9A). The transition between A1 and A2 corresponds to the powerstroke, and results in an increase in the length of the cross-bridge attachment of xps. The cross-bridge is modeled as a linear elastic element with stiffness κcb.

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