Varying thin filament activation in the framework of the Huxley'57 model

Abstract

Muscle contraction is triggered by the activation of the actin sites of the thin filament by calcium ions. It results that the thin filament activation level varies over time. Moreover, this activation process is also used as a regulation mechanism of the developed force. Our objective is to build a model of varying actin site activation level within the classical Huxley'57 two-state framework. This new model is obtained as an enhancement of a previously proposed formulation of the varying thick filament activation within the same framework [1]. We assume that the state of an actin site depends on whether it is activated and whether it forms a cross-bridge with the associated myosin head, which results in four possible states. The transitions between the actin site states are controlled by the global actin sites activation level and the dynamics of these transitions is coupled with the attachment-detachment process. A preliminary calibration of the model with experimental twitch contraction data obtained at varying sarcomere lengths is performed.

A jump-diffusion stochastic formalism for muscle contraction models at multiple timescales

“…A natural perspective would also be to couple our current model with a model of actin activation by calcium, which is essential to simulate the contraction of cardiac cells. Such coupling has already been formalized in the framework of the Huxley'57 model (Kimmig et al, 2022) and could be adjusted for our jump-diffusion model.…”