Fluid flow in the sarcomere

Abstract

A highly organized and densely packed lattice of molecular machinery within the sarcomeres of muscle cells powers contraction. Although many of the proteins that drive contraction have been studied extensively, the mechanical impact of fluid shearing within the lattice of molecular machinery has received minimal attention. It was recently proposed that fluid flow augments substrate transport in the sarcomere, however, this analysis used analytical models of fluid flow in the molecular machinery that could not capture its full complexity. By building a finite element model of the sarcomere, we estimate the explicit flow field, and contrast it with analytical models. Our results demonstrate that viscous drag forces on sliding filaments are surprisingly small in contrast to the forces generated by single myosin molecular motors. This model also indicates that the energetic cost of fluid flow through viscous shearing with lattice proteins is likely minimal. The model also highlights a steep velocity gradient between sliding filaments and demonstrates that the maximal radial fluid velocity occurs near the tips of the filaments. To our knowledge, this is the first computational analysis of fluid flow within the highly structured sarcomere.

A discontinuously coupled network of phase oscillators replicate actomyosin cooperation

“…The importance of viscous forces in synchronised and cooperative behaviour in this model is an interesting but not unexpected quality. The required values are greater than models for viscous drag within the sarcomere would suggest [51], however this aligns with the result found by Placais et al [9], who found the viscous friction coefficient required to obtain the expected coupling dynamics within their model was 2 to 3 orders of magnitude higher than predicted, whilst Julicher and Prost [17] used a damping coefficient assuming a viscosity 10 2 to 10 3 greater than water. The greater than expected restrictive force on filament movement is no longer generally thought to be caused just by the drag of negatively strained motors [28].…”

Why exercise builds muscles: titin mechanosensing controls skeletal muscle growth under load

“…However, if we assume that the internal energy dissipation in the thick filament-titin superstructure is minimal compared to the other sources of viscous energy dissipation (e.g., by filaments moving relative to their nearest neighbors), the force produced by the individual myosin motors during concentric muscle action will be directly related to the tension in the titin kinase domain. Furthermore, very recent work ( 71 ) suggests that viscous dissipation forces in the sarcomere are relatively minimal compared with active myosin force. Because of the inherent difficulty with any analysis of dissipative forces of this kind, we simply consider the microscopic TK tension to be directly proportional to the forces developed by the myosin motors attached to that filament.…”

Haemolymph viscosity in hawkmoths and its implications for hovering flight

“…The mean flow velocity through a slit-like pore of opening hav is proportional to the pore opening squared, hav2, and inversely proportional to haemolymph viscosity [58]. Therefore, the denser the muscle pack, the smaller the pore opening, and the stronger the pressure gradient needed to move haemolymph through the thorax [10]. And the greater the haemolymph viscosity, the greater the required pressure gradient.…”

“…To generate this pressure gradient, greater muscular action is demanded from the insect and, hence, greater metabolic energy is needed to do this mechanical work. For flying insects, viscosity is a major physiological parameter limiting flight performance by controlling the flow rate of fuel to the flight muscles, circulating nutrients and rapidly removing metabolic waste products [9][10][11][12].…”