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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.


Related in: MedlinePlus

Polar display of relative magnitude and direction of force F(θ) in the interaction area. A red arrow from the original point O represents force F(θ) in direction θ, and the red curve corresponds to the trace of the pointed end of force F(θ) with the change of load P. The direction of F(θ) at P=0 and P=Pmax is given by the directional angle of α+β (left end-point of the curve) and that of α+β+θmax =π (right end-point of the curve) from the H axis, respectively. Numerical values of F(θ) are calculated by Equation 13, in which the functional form of the ATPase rate is represented by the revised Hill’s formulae. The value of the constant heat production rate CHPR(θ) is assumed to be 0.05. It should be noted that the value of F(θ) is relative, and it depends on the expressive form of the ATPase rate. The sliding direction at Vp=0 is also shown.
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f10-5_11: Polar display of relative magnitude and direction of force F(θ) in the interaction area. A red arrow from the original point O represents force F(θ) in direction θ, and the red curve corresponds to the trace of the pointed end of force F(θ) with the change of load P. The direction of F(θ) at P=0 and P=Pmax is given by the directional angle of α+β (left end-point of the curve) and that of α+β+θmax =π (right end-point of the curve) from the H axis, respectively. Numerical values of F(θ) are calculated by Equation 13, in which the functional form of the ATPase rate is represented by the revised Hill’s formulae. The value of the constant heat production rate CHPR(θ) is assumed to be 0.05. It should be noted that the value of F(θ) is relative, and it depends on the expressive form of the ATPase rate. The sliding direction at Vp=0 is also shown.

Mentions: Force F(θ) given by Equation 13 is depicted in the interaction area by polar representation as functions of magnitude and sliding direction θ of force F(θ) (Fig. 10). The number of actin molecules on which a myosin head slides during τ is appended to the corresponding zone of the interaction area. The result indicates that a single actin molecule covers a wide range of sliding directions, especially under heavy load conditions. The sliding direction at Vp=0 is also shown.


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
Polar display of relative magnitude and direction of force F(θ) in the interaction area. A red arrow from the original point O represents force F(θ) in direction θ, and the red curve corresponds to the trace of the pointed end of force F(θ) with the change of load P. The direction of F(θ) at P=0 and P=Pmax is given by the directional angle of α+β (left end-point of the curve) and that of α+β+θmax =π (right end-point of the curve) from the H axis, respectively. Numerical values of F(θ) are calculated by Equation 13, in which the functional form of the ATPase rate is represented by the revised Hill’s formulae. The value of the constant heat production rate CHPR(θ) is assumed to be 0.05. It should be noted that the value of F(θ) is relative, and it depends on the expressive form of the ATPase rate. The sliding direction at Vp=0 is also shown.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC5036636&req=5

f10-5_11: Polar display of relative magnitude and direction of force F(θ) in the interaction area. A red arrow from the original point O represents force F(θ) in direction θ, and the red curve corresponds to the trace of the pointed end of force F(θ) with the change of load P. The direction of F(θ) at P=0 and P=Pmax is given by the directional angle of α+β (left end-point of the curve) and that of α+β+θmax =π (right end-point of the curve) from the H axis, respectively. Numerical values of F(θ) are calculated by Equation 13, in which the functional form of the ATPase rate is represented by the revised Hill’s formulae. The value of the constant heat production rate CHPR(θ) is assumed to be 0.05. It should be noted that the value of F(θ) is relative, and it depends on the expressive form of the ATPase rate. The sliding direction at Vp=0 is also shown.
Mentions: Force F(θ) given by Equation 13 is depicted in the interaction area by polar representation as functions of magnitude and sliding direction θ of force F(θ) (Fig. 10). The number of actin molecules on which a myosin head slides during τ is appended to the corresponding zone of the interaction area. The result indicates that a single actin molecule covers a wide range of sliding directions, especially under heavy load conditions. The sliding direction at Vp=0 is also shown.

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