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Fluctuation of actin sliding over myosin thick filaments in vitro

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ABSTRACT

It is customarily thought that myosin motors act as independent force-generators in both isotonic unloaded shortening as well as isometric contraction of muscle. We tested this assumption regarding unloaded shortening, by analyzing the fluctuation of the actin sliding movement over long native thick filaments from molluscan smooth muscle in vitro. This analysis is based on the prediction that the effective diffusion coefficient of actin, a measure of the fluctuation, is proportional to the inverse of the number of myosin motors generating the sliding movement of an actin filament, hence proportional to the inverse of the actin length, when the actions of the motors are stochastic and statistically independent. Contrary to this prediction, we found the effective diffusion coefficient to be virtually independent of, and thus not proportional to, the inverse of the actin length. This result shows that the myosin motors are not independent force-generators when generating the continuous sliding movement of actin in vitro and that the sliding motion is a macroscopic manifestation of the cooperative actions of the microscopic ensemble motors.

No MeSH data available.


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Variance of the actin sliding distance as a function of the time interval. The variance was calculated by averaging within the single linear trajectory shown in Fig. 2B. The filled line indicates an appropriate, initial linear portion of the curve of the data points (filled diamonds) for the determination of a Dm value by Eq. 1 (in Materials and methods). See the text for the method used to identify the appropriate, initial linear portion, and also for the Inset figure (filled circles: slope, crosses: <δ2>).
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f3-1_45: Variance of the actin sliding distance as a function of the time interval. The variance was calculated by averaging within the single linear trajectory shown in Fig. 2B. The filled line indicates an appropriate, initial linear portion of the curve of the data points (filled diamonds) for the determination of a Dm value by Eq. 1 (in Materials and methods). See the text for the method used to identify the appropriate, initial linear portion, and also for the Inset figure (filled circles: slope, crosses: <δ2>).

Mentions: The variance in the sliding displacements of an actin filament for various given time intervals was obtained by a single trajectory averaging with Eq. 1 (see Materials and methods). The variance is plotted against the time interval in Fig. 3, thus showing that the variance grew over time. This time-dependent term is due to the fluctuation inherent in the sliding motion rather than artifactual noises (see Imafuku et al. for further clarification14,16).


Fluctuation of actin sliding over myosin thick filaments in vitro
Variance of the actin sliding distance as a function of the time interval. The variance was calculated by averaging within the single linear trajectory shown in Fig. 2B. The filled line indicates an appropriate, initial linear portion of the curve of the data points (filled diamonds) for the determination of a Dm value by Eq. 1 (in Materials and methods). See the text for the method used to identify the appropriate, initial linear portion, and also for the Inset figure (filled circles: slope, crosses: <δ2>).
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC5036633&req=5

f3-1_45: Variance of the actin sliding distance as a function of the time interval. The variance was calculated by averaging within the single linear trajectory shown in Fig. 2B. The filled line indicates an appropriate, initial linear portion of the curve of the data points (filled diamonds) for the determination of a Dm value by Eq. 1 (in Materials and methods). See the text for the method used to identify the appropriate, initial linear portion, and also for the Inset figure (filled circles: slope, crosses: <δ2>).
Mentions: The variance in the sliding displacements of an actin filament for various given time intervals was obtained by a single trajectory averaging with Eq. 1 (see Materials and methods). The variance is plotted against the time interval in Fig. 3, thus showing that the variance grew over time. This time-dependent term is due to the fluctuation inherent in the sliding motion rather than artifactual noises (see Imafuku et al. for further clarification14,16).

View Article: PubMed Central - PubMed

ABSTRACT

It is customarily thought that myosin motors act as independent force-generators in both isotonic unloaded shortening as well as isometric contraction of muscle. We tested this assumption regarding unloaded shortening, by analyzing the fluctuation of the actin sliding movement over long native thick filaments from molluscan smooth muscle in vitro. This analysis is based on the prediction that the effective diffusion coefficient of actin, a measure of the fluctuation, is proportional to the inverse of the number of myosin motors generating the sliding movement of an actin filament, hence proportional to the inverse of the actin length, when the actions of the motors are stochastic and statistically independent. Contrary to this prediction, we found the effective diffusion coefficient to be virtually independent of, and thus not proportional to, the inverse of the actin length. This result shows that the myosin motors are not independent force-generators when generating the continuous sliding movement of actin in vitro and that the sliding motion is a macroscopic manifestation of the cooperative actions of the microscopic ensemble motors.

No MeSH data available.


Related in: MedlinePlus