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Load-dependent sliding direction change of a myosin head on an actin molecule and its energetic aspects: Energy borrowing model of a cross-bridge cycle

View Article: PubMed Central - PubMed

ABSTRACT

A model of muscle contraction is proposed, assuming loose coupling between power strokes and ATP hydrolysis of a myosin head. The energy borrowing mechanism is introduced in a cross-bridge cycle that borrows energy from the environment to cover the necessary energy for enthalpy production during sliding movement. Important premises for modeling are as follows: 1) the interaction area where a myosin head slides is supposed to be on an actin molecule; 2) the actomyosin complex is assumed to generate force F(θ), which slides the myosin head M* in the interaction area; 3) the direction of the force F(θ) varies in proportion to the load P; 4) the energy supplied by ATP hydrolysis is used to retain the myosin head in the high-energy state M*, and is not used for enthalpy production; 5) the myosin head enters a hydration state and dehydration state repeatedly during the cross-bridge cycle. The dehydrated myosin head recovers its hydrated state by hydration in the surrounding medium; 6) the energy source for work and heat production liberated by the AM* complex is of external origin. On the basis of these premises, the model adequately explains the experimental results observed at various levels in muscular samples: 1) twist in actin filaments observed in shortening muscle fibers; 2) the load-velocity relationship in single muscle fiber; 3) energy balance among enthalpy production, the borrowed energy and the energy supplied by ATP hydrolysis during muscle contraction. Force F(θ) acting on the myosin head is depicted.

No MeSH data available.


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Load-velocity relationship: Comparison of the theoretical indication and experimental data. Normalized load P/Pmax = θ/θmax vs. normalized velocity V/Vmax is plotted. It is assumed that (1) angle α+β+θ = π/2 at 1/2 Vmax; the myosin head slides along L-axis at V= 1/2 Vmax, and (2) α+β+θmax =π at isometric contraction, and (3) the numerical value of α is obtained by the inclination angle of the right-handed long-pitch strand on the radial projection; that of β is determined by the sliding direction at Vmax on the interaction unit of the radial projection. The results are in good agreement between the theoretical indication (solid line) and the experimental data (square) reported by Edman and Hwang (Fig. 2 of Edman & Hwang, 1977). Here, α and β are (67/180) π and (11/180) π radian, respectively.
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f6-5_11: Load-velocity relationship: Comparison of the theoretical indication and experimental data. Normalized load P/Pmax = θ/θmax vs. normalized velocity V/Vmax is plotted. It is assumed that (1) angle α+β+θ = π/2 at 1/2 Vmax; the myosin head slides along L-axis at V= 1/2 Vmax, and (2) α+β+θmax =π at isometric contraction, and (3) the numerical value of α is obtained by the inclination angle of the right-handed long-pitch strand on the radial projection; that of β is determined by the sliding direction at Vmax on the interaction unit of the radial projection. The results are in good agreement between the theoretical indication (solid line) and the experimental data (square) reported by Edman and Hwang (Fig. 2 of Edman & Hwang, 1977). Here, α and β are (67/180) π and (11/180) π radian, respectively.

Mentions: As shown in Figure 6, the theoretically derived, normalized load-velocity relationship V(θ)/Vmax is consistent with the experimental data from single muscle fibers18 (Fig. 2 of Edman & Hwang, 1977). This result indicates that Premise 6 is appropriate, even under heavy-load conditions, including the isometric condition, where θ becomes larger and the myosin head slides in the interaction area of a single actin molecule throughout the duration of time t(P) (as shown in Fig. 4A). While under these conditions, the ATPase rate of the myosin head becomes slower than that of the maximum rate.


Load-dependent sliding direction change of a myosin head on an actin molecule and its energetic aspects: Energy borrowing model of a cross-bridge cycle
Load-velocity relationship: Comparison of the theoretical indication and experimental data. Normalized load P/Pmax = θ/θmax vs. normalized velocity V/Vmax is plotted. It is assumed that (1) angle α+β+θ = π/2 at 1/2 Vmax; the myosin head slides along L-axis at V= 1/2 Vmax, and (2) α+β+θmax =π at isometric contraction, and (3) the numerical value of α is obtained by the inclination angle of the right-handed long-pitch strand on the radial projection; that of β is determined by the sliding direction at Vmax on the interaction unit of the radial projection. The results are in good agreement between the theoretical indication (solid line) and the experimental data (square) reported by Edman and Hwang (Fig. 2 of Edman & Hwang, 1977). Here, α and β are (67/180) π and (11/180) π radian, respectively.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC5036636&req=5

f6-5_11: Load-velocity relationship: Comparison of the theoretical indication and experimental data. Normalized load P/Pmax = θ/θmax vs. normalized velocity V/Vmax is plotted. It is assumed that (1) angle α+β+θ = π/2 at 1/2 Vmax; the myosin head slides along L-axis at V= 1/2 Vmax, and (2) α+β+θmax =π at isometric contraction, and (3) the numerical value of α is obtained by the inclination angle of the right-handed long-pitch strand on the radial projection; that of β is determined by the sliding direction at Vmax on the interaction unit of the radial projection. The results are in good agreement between the theoretical indication (solid line) and the experimental data (square) reported by Edman and Hwang (Fig. 2 of Edman & Hwang, 1977). Here, α and β are (67/180) π and (11/180) π radian, respectively.
Mentions: As shown in Figure 6, the theoretically derived, normalized load-velocity relationship V(θ)/Vmax is consistent with the experimental data from single muscle fibers18 (Fig. 2 of Edman & Hwang, 1977). This result indicates that Premise 6 is appropriate, even under heavy-load conditions, including the isometric condition, where θ becomes larger and the myosin head slides in the interaction area of a single actin molecule throughout the duration of time t(P) (as shown in Fig. 4A). While under these conditions, the ATPase rate of the myosin head becomes slower than that of the maximum rate.

View Article: PubMed Central - PubMed

ABSTRACT

A model of muscle contraction is proposed, assuming loose coupling between power strokes and ATP hydrolysis of a myosin head. The energy borrowing mechanism is introduced in a cross-bridge cycle that borrows energy from the environment to cover the necessary energy for enthalpy production during sliding movement. Important premises for modeling are as follows: 1) the interaction area where a myosin head slides is supposed to be on an actin molecule; 2) the actomyosin complex is assumed to generate force F(θ), which slides the myosin head M* in the interaction area; 3) the direction of the force F(θ) varies in proportion to the load P; 4) the energy supplied by ATP hydrolysis is used to retain the myosin head in the high-energy state M*, and is not used for enthalpy production; 5) the myosin head enters a hydration state and dehydration state repeatedly during the cross-bridge cycle. The dehydrated myosin head recovers its hydrated state by hydration in the surrounding medium; 6) the energy source for work and heat production liberated by the AM* complex is of external origin. On the basis of these premises, the model adequately explains the experimental results observed at various levels in muscular samples: 1) twist in actin filaments observed in shortening muscle fibers; 2) the load-velocity relationship in single muscle fiber; 3) energy balance among enthalpy production, the borrowed energy and the energy supplied by ATP hydrolysis during muscle contraction. Force F(θ) acting on the myosin head is depicted.

No MeSH data available.


Related in: MedlinePlus