Physics of Muscle Contraction

Report on Progress in Physics, 81: 036602 🔗 📘

Abstract

In this paper we report, clarify and broaden various recent efforts to complement the chemistry-centered models of force generation in (skeletal) muscles by mechanics-centered models. The physical mechanisms of interest can be grouped into two classes: passive and active. The main passive effect is the fast force recovery which does not require the detachment of myosin cross-bridges from actin filaments and can operate without a specialized supply of metabolic fuel (ATP). In mechanical terms, it can be viewed as a collective folding-unfolding phenomenon in the system of interacting bi-stable units and modeled by near equilibrium Langevin dynamics. The parallel active force generation mechanism operates at slow time scales, requires detachment and is crucially dependent on ATP hydrolysis. The underlying mechanical processes take place far from equilibrium and are represented by stochastic models with broken time reversal symmetry implying non-potentiality, correlated noise or multiple reservoirs. The modeling approaches reviewed in this paper deal with both active and passive processes and support from the mechanical perspective the biological point of view that phenomena involved in slow (active) and fast (passive) force generation are tightly intertwined. They reveal, however, that biochemical studies in solution, macroscopic physiological measurements and structural analysis do not provide by themselves all the necessary insights into the functioning of the organized contractile system. In particular, the reviewed body of work emphasizes the important role of long-range interactions and criticality in securing the targeted mechanical response in the physiological regime of isometric contractions. The importance of the purely mechanical microscale modeling is accentuated at the end of the paper where we address the puzzling issue of the stability of muscle response on the so-called “descending limb” of the isometric tetanus.

Main contribution

This publication serves as a review primarily focusing on my theoretical research concerning collective conformational changes within ensembles of molecular motors.

The review underscores the significant role of elastic interactions between molecular motors in precipitating collective effects, such as power-stroke synchronization. These interactions are facilitated by sarcomeric structural proteins that bundle the motors together. The elastic properties of these proteins govern the emergence of synchronized phases.

This study suggests that the prevalent mean-field models for molecular motors might neglect these collective effects.

Furthermore, it highlights the crucial role the entangled network of structural proteins at the mesoscale plays in transmitting the active force, generated at the nanoscale, to the entire tissue at the macroscale.

Reference

@article{caruel-2018a,
  title = {Physics of Muscle Contraction},
  author = {Caruel, M and Truskinovsky, L},
  year = {2018},
  month = mar,
  journal = {Reports on Progress in Physics},
  volume = {81},
  number = {3},
  pages = {036602},
  doi = {10/gf8wq6},
  langid = {en},
}