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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 difference between the sums of the positions of the centers of mass of the myosin arrays, at the beginning and at the end of phase 2, as a function of the tilt angles of the detached head domains. The upper limit of the attached head domains was set to 32%. The average angle of tilt was 140° at the beginning of the second phase and 104° at the end of the second phase. The angle of tilt of the detached head domains was selected at random between: 1 detached coupled with detached head domain, 150°–70°; detached coupled with attached head domain, 120°–90° (empty diamond): 2 all the detached head domains tilt between 150° and 40° (filled diamond); 3 all the detached head domains are at 90° (filled circle). The size of the working stroke is at −5.1364 nm.
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ijms-16-12064-f003: The difference between the sums of the positions of the centers of mass of the myosin arrays, at the beginning and at the end of phase 2, as a function of the tilt angles of the detached head domains. The upper limit of the attached head domains was set to 32%. The average angle of tilt was 140° at the beginning of the second phase and 104° at the end of the second phase. The angle of tilt of the detached head domains was selected at random between: 1 detached coupled with detached head domain, 150°–70°; detached coupled with attached head domain, 120°–90° (empty diamond): 2 all the detached head domains tilt between 150° and 40° (filled diamond); 3 all the detached head domains are at 90° (filled circle). The size of the working stroke is at −5.1364 nm.

Mentions: The proposition of Reconditi et al. [3], that the difference between the interference distances at the beginning and at the end of phase 2 equals the stroke size, is verified only if the cross-bridges are all attached and with the same angle of tilt. On the contrary, the proposition of Reconditi et al. [3] fails when the fraction of the attached cross-bridges is below 100%, even though the angle of tilt of the detached cross-bridges is set to 90°, to neutralize their influence on the position of the center of mass of the myosin arrays. Even more the proposition of Reconditi et al. [3] fails when the attached cross-bridges are below 100% and the angles of tilt of detached cross-bridges are selected at random (Figure 3).


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

Grazi E - Int J Mol Sci (2015)

The difference between the sums of the positions of the centers of mass of the myosin arrays, at the beginning and at the end of phase 2, as a function of the tilt angles of the detached head domains. The upper limit of the attached head domains was set to 32%. The average angle of tilt was 140° at the beginning of the second phase and 104° at the end of the second phase. The angle of tilt of the detached head domains was selected at random between: 1 detached coupled with detached head domain, 150°–70°; detached coupled with attached head domain, 120°–90° (empty diamond): 2 all the detached head domains tilt between 150° and 40° (filled diamond); 3 all the detached head domains are at 90° (filled circle). The size of the working stroke is at −5.1364 nm.
© Copyright Policy
Related In: Results  -  Collection

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

ijms-16-12064-f003: The difference between the sums of the positions of the centers of mass of the myosin arrays, at the beginning and at the end of phase 2, as a function of the tilt angles of the detached head domains. The upper limit of the attached head domains was set to 32%. The average angle of tilt was 140° at the beginning of the second phase and 104° at the end of the second phase. The angle of tilt of the detached head domains was selected at random between: 1 detached coupled with detached head domain, 150°–70°; detached coupled with attached head domain, 120°–90° (empty diamond): 2 all the detached head domains tilt between 150° and 40° (filled diamond); 3 all the detached head domains are at 90° (filled circle). The size of the working stroke is at −5.1364 nm.
Mentions: The proposition of Reconditi et al. [3], that the difference between the interference distances at the beginning and at the end of phase 2 equals the stroke size, is verified only if the cross-bridges are all attached and with the same angle of tilt. On the contrary, the proposition of Reconditi et al. [3] fails when the fraction of the attached cross-bridges is below 100%, even though the angle of tilt of the detached cross-bridges is set to 90°, to neutralize their influence on the position of the center of mass of the myosin arrays. Even more the proposition of Reconditi et al. [3] fails when the attached cross-bridges are below 100% and the angles of tilt of detached cross-bridges are selected at random (Figure 3).

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