Muscle contraction and the elasticity-mediated crosstalk effect

TL;DR

This paper uses statistical mechanics to analyze how elasticity-mediated crosstalk affects molecular motor coordination in muscle sarcomeres, revealing size-dependent effects and linking tension to motor duty ratio.

Contribution

It introduces a detailed analysis of EMC effects on motor attachment probabilities and explains the size limitation of sarcomeres, connecting muscle tension to Hill's equation.

Findings

EMC causes polarized motor attachment in sarcomeres.

Size of the system influences EMC impact, explaining sarcomere uniformity.

Muscle tension increases motor duty ratio, consistent with Hill's law.

Abstract

Cooperative action of molecular motors is essential for many cellular processes. One possible regulator of motor coordination is the elasticity-mediated crosstalk (EMC) coupling between myosin II motors whose origin is the tensile stress that they collectively generate in actin filaments. Here, we use a statistical mechanical analysis to investigate the influence of the EMC effect on the sarcomere - the basic contractile unit of skeletal muscles. We demonstrate that the EMC effect leads to an increase in the attachment probability of motors located near the end of the sarcomere while, simultaneously, decreasing the attachment probability of the motors in the central part. Such a polarized attachment probability would impair the motors ability to cooperate efficiently. Interestingly, this undesired phenomenon becomes significant only when the system size exceeds that of the sarcomere in skeletal muscles, which provides an explanation for the remarkable lack of sarcomere variability in vertebrates. Another phenomenon that we investigate is the recently observed increase in the duty ratio of the motors with the tension in muscle. We reveal that the celebrated Hill's equation for muscle contraction is very closely related to this observation.