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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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Simulation of a half-sarcomere experiencing a 30 Hz length oscillation.The simulation is described in detail in the text, and the parameters used are found in Table 1. (a) Force-response time-trace of the half-sarcomere. (b) Percent of strongly bound cross-bridges (i.e. in one of the attached states) as a function of time.
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pone.0121726.g010: Simulation of a half-sarcomere experiencing a 30 Hz length oscillation.The simulation is described in detail in the text, and the parameters used are found in Table 1. (a) Force-response time-trace of the half-sarcomere. (b) Percent of strongly bound cross-bridges (i.e. in one of the attached states) as a function of time.

Mentions: The simulation described above was run with the parameters in Table 1. The force response of the fibers was sinusoidal, and consistent with our hypothesis, the half-sarcomere exhibited thixotropy for frequencies of 5 Hz and higher (Fig 10A). Plotting the percent of strongly-bound cross-bridges as a function of time during the oscillation (Fig 10B) shows that this change in the mechanical properties of the fiber results from a change in the number of bound cross-bridges within a sarcomere


Thixotropy and rheopexy of muscle fibers probed using sinusoidal oscillations.

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

Simulation of a half-sarcomere experiencing a 30 Hz length oscillation.The simulation is described in detail in the text, and the parameters used are found in Table 1. (a) Force-response time-trace of the half-sarcomere. (b) Percent of strongly bound cross-bridges (i.e. in one of the attached states) as a function of time.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0121726.g010: Simulation of a half-sarcomere experiencing a 30 Hz length oscillation.The simulation is described in detail in the text, and the parameters used are found in Table 1. (a) Force-response time-trace of the half-sarcomere. (b) Percent of strongly bound cross-bridges (i.e. in one of the attached states) as a function of time.
Mentions: The simulation described above was run with the parameters in Table 1. The force response of the fibers was sinusoidal, and consistent with our hypothesis, the half-sarcomere exhibited thixotropy for frequencies of 5 Hz and higher (Fig 10A). Plotting the percent of strongly-bound cross-bridges as a function of time during the oscillation (Fig 10B) shows that this change in the mechanical properties of the fiber results from a change in the number of bound cross-bridges within a sarcomere

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