Research Papers

Self-Regulation of Motor Force Through Chemomechanical Coupling in Skeletal Muscle Contraction

[+] Author and Article Information
Bin Chen

Department of Engineering Mechanics,
Zhejiang University,
Hangzhou 310027, PRC
e-mail: chenb6@zju.edu.cn

Manuscript received October 23, 2012; final manuscript received November 28, 2012; accepted manuscript posted February 14, 2013; published online July 12, 2013. Editor: Yonggang Huang.

J. Appl. Mech 80(5), 051013 (Jul 12, 2013) (5 pages) Paper No: JAM-12-1490; doi: 10.1115/1.4023680 History: Received October 23, 2012; Revised November 28, 2012; Accepted February 14, 2013

It is intriguing how the mechanics of molecular motors is regulated to perform the mechanical work in living systems. In sharp contrast to the conventional wisdom, recent experiments indicated that motor force maintains ∼6 pN upon a wide range of filament loads during skeletal muscle contraction at the steady state. Here we find that this rather precise regulation which takes place in an essentially chaotic system, can be due to that a “working” motor is arrested in a transitional state when the motor force is ∼6 pN. Our analysis suggests that the motor force can be self-regulated through chemomechanical coupling, and motor force homeostasis is a built-in feature at the level of a single motor, which provides insights to understanding the coordinated function of multiple molecular motors existing in various physiological processes. With a coupled stochastic-elastic numerical framework, the kinetic model for a Actin-myosin-ATP cycle constructed in this work might pave the way to decently investigate the transient behaviors of the skeletal muscle or other actomyosin complex structures.

Copyright © 2013 by ASME
Topics: Engines , Muscle , Cycles
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Fig. 1

Six kinetic states are assigned in the kinetic model to a myosin motor within an actin-myosin-ATP cycle. “Idle” state is when myosin is off the actin and a “working” motor stays in any of the rest states.

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Fig. 2

In this mechanics model of a “working” motor, the elasticity is accounted for by a linear spring, which is in series with a rigid lever arm that swings. The swing rate depends on the motor force within the linear spring and the swing is arrested when the motor force is ∼6 pN. The maximal swing distance is ∼6 nm.

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Fig. 3

Dominant rate constant r of quick recovery following a length step in the transient T2 test: diamonds are the experimental data; solid lines are the respective fitting curves for the lengthening and the shortening

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Fig. 4

(a) Schematics of a mechanics model for sarcomere: the elasticity of filaments is not considered, the sacromere is at the isomeric state initially, and its right end is then subjected to a step perturbation of velocity V; (b) flow chart of using a First Reaction method to simulate the average force on a “working” motor against perturbation displacement

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Fig. 5

(a) Solid lines represent the average force on a “working” motor against perturbation displacement at various perturbation velocities obtained from the simulation and the dashed line is the schematics of the unique force-stretch curve of a “working” motor extracted from the T2 curve in the transient test. Note that detachment or attachment of motors is not considered in the simulation; (b) the schematics of the force-stretch curve of a single “working” motor during skeletal muscle contraction at the steady state, as intuitively deduced from its kinetic process.




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