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. Related in: MedlinePlus |
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Mentions: Likewise, we repeated the fluctuation analysis with thick filaments (8 in total) isolated from the same animal of S. virgatus used for the analysis shown in Figs. 2 and 3, to evaluate the effective diffusion coefficients of individual actin filaments sliding over the myosin filaments. The effective diffusion coefficients thus evaluated are plotted against the actin filament length in Fig. 4A (filled circles). The open squares in this figure show another example of the results from the same analysis, which was carried out with myosin filaments isolated from an animal of another species, M. galloprovincialis. As shown in Fig. 4A, the effective diffusion coefficient of actin filaments is not proportional to 1/(actin length); the coefficient does not appreciably depend on the actin length in both bivalves. This is in sharp contrast to the prediction of the inverse length dependence derived from the assumption of the stochastic and statistically random actions of myosin motors. |
View Article: PubMed Central - PubMed
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.