Meeting Abstract
Cells interact dynamically with their environment, often altering their structure in response to stimuli. Architectural changes within cells occur in a (generally) small fluid filled environment, where viscous forces overwhelm inertia. Within muscle, the sliding filament hypothesis has described the cyclic architectural changes that occur within the sarcomere in order to accomplish large scale cellular, and ultimately, muscular contraction. Each sarcomere is percolated by cytoplasm, and it remains unknown how this fluid impacts muscle function as the thick and thin filaments slide past one another during contractions. We hypothesize that viscous shear forces between cytoplasm and moving filaments results in an energy expense that has not been quantified. To understand forces and energetics at this small, low Reynolds number scale, we used the singularity method to simulate Stokes flow in a lattice of thick and thin filaments. Using this model, we estimate that the viscous drag force on a single thick filament in the sarcomere half space to be between 2.5 and 25 e-3 pN, depending on the cytoplasm’s viscosity. For an entire sarcomere consisting of about 500 thick filaments and 3000 thin filaments we estimate the total rate of energy dissipation resulting from this viscous force to be between 175 and 1750 ATP per second. Our results suggest that viscous shearing in the sarcomere can represent an important avenue of energy dissipation.
