Physics of muscle contraction

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 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 micro-scale 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.

Different motilities of microtubules driven by kinesin-1 and kinesin-14 motors patterned on nanopillars

“…Motor proteins convert chemical energy into structural changes and produce mechanical work necessary for various cellular processes including vesicle transport (1), cell division (2), muscle contraction (3), and beating of flagella and cilia (4). In vivo, motor proteins do not work alone but as a team (5)(6)(7).…”

The dynamics of the skeletal muscle: A systems biophysics perspective on muscle modeling with the focus on Hill‐type muscle models

“…[30] Hill-type [19,[31][32][33][34][35][36][37][38] and Huxley-type [23,29,[39][40][41][42][43][44][45][46][47][48] models have been further developed until today. There are-mainly more recent-attempts [6,[49][50][51][52][53][54][55][56] which have tried to conflate Hill-type and Huxley-type models. As mentioned above, such former, conflated muscle models [57][58][59] have concentrated on electromechanical coupling so far, and are the currently most complex ones.…”

Thermodynamics of small systems with conformational transitions: The case of two-state freely jointed chains with extensible units

“…78 Finally, it is interesting to remark that the statistical mechanics and the dynamics of systems with multi-well energy are useful to model other physical situations including, but not limited to, cell adhesion, macromolecular hairpins, skeletal muscles, ferromagnetic alloys, nano-indented substrates, and plastic materials. 71,75,77,80…”

“…72,73 This method has been recently applied to different allosteric systems and macromolecular chains as well. [74][75][76][77] The introduction of the spin variables is advantageous since it strongly facilitates the calculation of the partition functions, preserving at the same time good accuracy of results. 76 Briefly, an arbitrary potential function composed of two minima can be substituted by two quadratic potentials and the switching between them is controlled by the corresponding spin variable.…”