TANNER, B.C.W.; DANIEL, T.L.; Univ. of Washington; Univ. of Washington: Modeling work loops from molecular motors: filament compliance determines ATP consumption.

Work loops have become an important method for characterizing the mechanical performance of muscles undergoing cyclic length changes. While such methods provide a clear measure of mechanical power output, they do not reveal the required energy input corresponding to specific patterns of muscle activation and length change. ATP consumption, a key measure of energy input, may depend on the activation pattern and mechanical design of the myofilament lattice in such a way that the conditions yielding maximal efficiency (the ratio power output to power input) may not yield maximal mechanical power output. To explore the relationship between ATPase rate and mechanical power output we use a spatially explicit model of myosin motors immersed in a lattice of compliant filaments. The model is based on a dynamic force balance in which cross-bridges may attach or detach from thin filaments. We use Monte-Carlo methods to control cross-bridge cycling kinetics. The model predicts average force as well as ATP consumption, while allowing simulated excitation and imposed length changes on the compliant myofilament lattice. We find that both phase of activation and filament compliance affect ATP consumption and thus efficiency of muscle contraction.