Fluid flow in the sarcomere

TL;DR

This study presents the first computational model of fluid flow within the sarcomere, revealing minimal viscous drag forces and highlighting the velocity gradients near filament tips, which could influence muscle contraction mechanics.

Contribution

The paper introduces a finite element model of sarcomere fluid dynamics, providing detailed insights into flow fields and forces that were previously approximated analytically.

Findings

Viscous drag forces are small compared to myosin motor forces.

Energetic cost of fluid flow is likely minimal.

Steep velocity gradient observed near filament tips.

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.