A sliding-filament cross-bridge ensemble model of muscle contraction for mechanical transients

Abstract

A high-efficiency mechanochemical model of contraction for striated muscle is developed via the formalism of statistical mechanics. The myosin cross-bridges of the half-sarcomere ensemble cycle through five biochemical states. The structural components of the sliding-filament system include extensible myosin S2-units and indefinite arrays of equivalent actin sites. ATP ligand exchanges provide the far-from-equilibrium thermodynamic driving potential for cross-bridge cycling. The strain-dependent rate constants obey the self-consistency requirements of detailed balance. The mathematical solution for the linear time-varying system of equations of cross-bridge biokinetics employs discrete-time state transition matrices. Computer simulations describe the time evolution of ultrastructural (macromolecular) phenomena and their ensemble (macroscopic) averages. Modest fidelity for mechanical transients of muscle under many varied protocols, including conditions of fatique, is obtained between the simulations and their experimental counterpart.