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The cross-bridge of skeletal muscle is not synchronized either by length or force step.

Grazi E - Int J Mol Sci (2015)

Bottom Line: A rapid force step does not synchronize attached cross-bridges.The change of X-ray interference during the second phase does not measure the stroke size.These conclusions significantly change the picture of the mechanism of skeletal muscle contraction.

View Article: PubMed Central - PubMed

Affiliation: Department of Scienze Biomediche e Chirurgiche Specialistiche, Ferrara University, Via Borsari 46, 44121 Ferrara, Italy. enrico.grazi@unife.it.

ABSTRACT
Force and length steps, applied to a muscle fiber in the isometric state, are believed to synchronize attached cross-bridges. This alleged synchronization facilitates the interpretation of the experiments. A rapid force step elicits an elastic response of the attached cross-bridges, followed by an isotonic phase. The decay of this second isotonic phase is of the first order. This excludes that the attached cross-bridges may decay all at the same time. The change of the X-ray interference distance during the second phase measures the stroke size only in the unrealistic case that the cross-bridges are and remain all attached. A rapid force step does not synchronize attached cross-bridges. The change of X-ray interference during the second phase does not measure the stroke size. These conclusions significantly change the picture of the mechanism of skeletal muscle contraction.

No MeSH data available.


Related in: MedlinePlus

The decay of phase 2 as a first order phenomenon. Data are taken from figure 1B of Piazzesi et al. [2]. For drawing the graph the length zero of figure 1B is used as a common origin. The origin of the different traces is obtained by subtracting, from the common origin, the shortening simultaneous with the force step, L1 (Figure 2A of Piazzesi et al. [2]. Filled diamond, 0.3 T0; open circle, 0.7 T0; filled circle, 0.8 T0. The continuous lines are obtained by the equation, l = l0 Exp[−k t].
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ijms-16-12064-f002: The decay of phase 2 as a first order phenomenon. Data are taken from figure 1B of Piazzesi et al. [2]. For drawing the graph the length zero of figure 1B is used as a common origin. The origin of the different traces is obtained by subtracting, from the common origin, the shortening simultaneous with the force step, L1 (Figure 2A of Piazzesi et al. [2]. Filled diamond, 0.3 T0; open circle, 0.7 T0; filled circle, 0.8 T0. The continuous lines are obtained by the equation, l = l0 Exp[−k t].

Mentions: The hypothesis that the rapid phase 2 is related to the synchronous execution of the working stroke is disproved by the data themselves of Piazzesi et al. [2]. Their figure 1B shows that phase 2 decays with the apparent first order rate constants of 1300 s−1 at 0.3 T0, of 1400 s−1 at 0.5 T0, of 750 s−1 at 0.7 T0 and of 400 s−1 at 0.8 T0 (Figure 2).


The cross-bridge of skeletal muscle is not synchronized either by length or force step.

Grazi E - Int J Mol Sci (2015)

The decay of phase 2 as a first order phenomenon. Data are taken from figure 1B of Piazzesi et al. [2]. For drawing the graph the length zero of figure 1B is used as a common origin. The origin of the different traces is obtained by subtracting, from the common origin, the shortening simultaneous with the force step, L1 (Figure 2A of Piazzesi et al. [2]. Filled diamond, 0.3 T0; open circle, 0.7 T0; filled circle, 0.8 T0. The continuous lines are obtained by the equation, l = l0 Exp[−k t].
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4490429&req=5

ijms-16-12064-f002: The decay of phase 2 as a first order phenomenon. Data are taken from figure 1B of Piazzesi et al. [2]. For drawing the graph the length zero of figure 1B is used as a common origin. The origin of the different traces is obtained by subtracting, from the common origin, the shortening simultaneous with the force step, L1 (Figure 2A of Piazzesi et al. [2]. Filled diamond, 0.3 T0; open circle, 0.7 T0; filled circle, 0.8 T0. The continuous lines are obtained by the equation, l = l0 Exp[−k t].
Mentions: The hypothesis that the rapid phase 2 is related to the synchronous execution of the working stroke is disproved by the data themselves of Piazzesi et al. [2]. Their figure 1B shows that phase 2 decays with the apparent first order rate constants of 1300 s−1 at 0.3 T0, of 1400 s−1 at 0.5 T0, of 750 s−1 at 0.7 T0 and of 400 s−1 at 0.8 T0 (Figure 2).

Bottom Line: A rapid force step does not synchronize attached cross-bridges.The change of X-ray interference during the second phase does not measure the stroke size.These conclusions significantly change the picture of the mechanism of skeletal muscle contraction.

View Article: PubMed Central - PubMed

Affiliation: Department of Scienze Biomediche e Chirurgiche Specialistiche, Ferrara University, Via Borsari 46, 44121 Ferrara, Italy. enrico.grazi@unife.it.

ABSTRACT
Force and length steps, applied to a muscle fiber in the isometric state, are believed to synchronize attached cross-bridges. This alleged synchronization facilitates the interpretation of the experiments. A rapid force step elicits an elastic response of the attached cross-bridges, followed by an isotonic phase. The decay of this second isotonic phase is of the first order. This excludes that the attached cross-bridges may decay all at the same time. The change of the X-ray interference distance during the second phase measures the stroke size only in the unrealistic case that the cross-bridges are and remain all attached. A rapid force step does not synchronize attached cross-bridges. The change of X-ray interference during the second phase does not measure the stroke size. These conclusions significantly change the picture of the mechanism of skeletal muscle contraction.

No MeSH data available.


Related in: MedlinePlus