Analysis of a simple prototypal muscle model near to and far from equilibrium.

Accurate calculations of force generated and of ATP flux, in steady isotonic contractions, are made on a simple, two-state muscle model of the sliding filament type. The objective is to illustrate the proper formulation and use of a complete and self-consistent molecular model of muscle. Otherwise, the model is not meant to be realistic. Calculations were made near equilibrium, including linear and quadratic terms in a power series expansion, and arbitrarily far from equilibrium by direct numerical solution of the appropriate differential equation in the probability of cross-bridge attachment. The results obtained from the two different methods agree where they overlap near equilibrium. The efficiency of free energy conversion is emphasized, and the relation to linear irreversible thermodynamics is pointed out.