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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

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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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Relationship among the power of energy supplied by single ATP hydrolysis ATPR(θ)·Eatp, the power of the constant heat component CHPR(θ), and the power of the gross work (θ) of a myosin head. The functional form of the power of energy supplied by ATP hydrolysis is assumed to be the same as the enthalpy production rate (shown in Fig. 8) given by the revised Hill’s formulae. The maintenance heat rate m, which is the power of maintenance heat given by Hill’ formulae is also shown.
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f9-5_11: Relationship among the power of energy supplied by single ATP hydrolysis ATPR(θ)·Eatp, the power of the constant heat component CHPR(θ), and the power of the gross work (θ) of a myosin head. The functional form of the power of energy supplied by ATP hydrolysis is assumed to be the same as the enthalpy production rate (shown in Fig. 8) given by the revised Hill’s formulae. The maintenance heat rate m, which is the power of maintenance heat given by Hill’ formulae is also shown.

Mentions: This premise indicates that the energy balance observed in shortening muscle is also realized in a single myosin head during the sliding movement in the interaction area. Relationships among the power of the gross work (θ), the power of energy supplied by ATP hydrolysis ATPR(θ)·Eatp, and that of CHPR(θ) are explained in Figure 9. The constant heat-production rate CHPR(θ), which resembles the maintenance heat rate in Hill’s formulae, is assumed to be independent of the sliding velocity of the myosin head, and it is not transformed into gross work. The value of CHPR(θ) is tentatively assumed to be 0.05. This value is less than 0.0629 of the maintenance heat rate (m) in Hill’s formulae that is calculated assuming the normalized load-velocity relationship shown in Figure 6, because the gross work Wg(θ) has a positive value under isometric contraction. The myosin head is still sliding on the interaction unit along the H-axis under the isometric condition with sliding velocity Vu(θmax), while the shortening velocity V(θ) along the L-axis is equal to zero.


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
Relationship among the power of energy supplied by single ATP hydrolysis ATPR(θ)·Eatp, the power of the constant heat component CHPR(θ), and the power of the gross work (θ) of a myosin head. The functional form of the power of energy supplied by ATP hydrolysis is assumed to be the same as the enthalpy production rate (shown in Fig. 8) given by the revised Hill’s formulae. The maintenance heat rate m, which is the power of maintenance heat given by Hill’ formulae is also shown.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC5036636&req=5

f9-5_11: Relationship among the power of energy supplied by single ATP hydrolysis ATPR(θ)·Eatp, the power of the constant heat component CHPR(θ), and the power of the gross work (θ) of a myosin head. The functional form of the power of energy supplied by ATP hydrolysis is assumed to be the same as the enthalpy production rate (shown in Fig. 8) given by the revised Hill’s formulae. The maintenance heat rate m, which is the power of maintenance heat given by Hill’ formulae is also shown.
Mentions: This premise indicates that the energy balance observed in shortening muscle is also realized in a single myosin head during the sliding movement in the interaction area. Relationships among the power of the gross work (θ), the power of energy supplied by ATP hydrolysis ATPR(θ)·Eatp, and that of CHPR(θ) are explained in Figure 9. The constant heat-production rate CHPR(θ), which resembles the maintenance heat rate in Hill’s formulae, is assumed to be independent of the sliding velocity of the myosin head, and it is not transformed into gross work. The value of CHPR(θ) is tentatively assumed to be 0.05. This value is less than 0.0629 of the maintenance heat rate (m) in Hill’s formulae that is calculated assuming the normalized load-velocity relationship shown in Figure 6, because the gross work Wg(θ) has a positive value under isometric contraction. The myosin head is still sliding on the interaction unit along the H-axis under the isometric condition with sliding velocity Vu(θmax), while the shortening velocity V(θ) along the L-axis is equal to zero.

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