Athermal Fluctuations of Probe Particles in Active Cytoskeletal Network

Abstract

A reconstituted active cytoskeletal networks consisting of an actin filament network coupled to myosins (motor proteins) have been shown to display rich in dynamical and mechanical behaviors that is often in contrast to passive, equilibrium system. The motor proteins, which spontaneously generate forces, kept the active cytoskeletal network out of equilibrium. The athermal fluctuations observed in the network are linked to the active force generation by motor proteins which give more relevant information including the interaction with the surrounding materials. In prior studies, only the second moment--also referred to as the mean square displacement or power spectral density--of the athermal fluctuations has been investigated. In equilibrium where the Gaussian statistics are implied, second moment analysis supplies all the necessary information to characterize the fluctuation. There is no reason a priori to expect Gaussian statistics in non-equilibrium systems. Indeed, the full displacement distribution of the athermal fluctuations in active cytoskeleton recently probed using video microrheology is found to be far from Gauss. No theoretical model has been found yet that describes the non-Gaussian signature of the distribution. Therefore, in this study, we examine the non-equilibrium statistics and dynamics of the active network by analyzing the athermal fluctuations using a new theoretical model developed by I. Zaid, et al. The model, which is based on Levy statistics, incorporates the thermal and athermal fluctuations and assumes that a single myosin acts as a force dipole. In our results, it was found out the full displacement distribution follows truncated Levy statistics distribution. Sum action of multiple motor proteins, which drives the probe particle, only slowly converges to Gauss distribution because of the 1/r2 spatial decay of the motor impacts.