Slow filament dynamics and viscoelasticity in entangled and active actin networks

Abstract

This paper deals with correlations between the viscoelastic impedance of entangled actin networks and the slow conformational dynamics and diffusive motions of single filaments. The single filament dynamics is visualized and analysed by analysing the Brownian motion of attached colloidal beads, which enables independent measurements of characteristic viscoelastic response times such as the entanglement and reptation times. We further studied the frequency-dependent viscoelastic impedance of active actin-heavy-meromyosin II networks by magnetic-tweezers microrheometry to gain insight into the effect of such highly dynamic and force-generating crosslinkers (exhibiting bond lifetimes of less than 1 s) on the rheological properties. We show that at high frequencies (higher than 1 Hz) the viscoelastic loss modulus is slightly increased relative to the entangled network (associated with an increase in the energy dissipated during mechanical excitations), while at low frequencies the plateau of the impedance spectrum becomes more pronounced as a consequence of the cross-linking of the network and the suppression of the terminal regime. Our data provide evidence that the myosin motor protein may play a role as softener of the actin cortex, enabling the adaptive reduction of the yield stress of cells and thus facilitating cellular deformations.

A quantitative examination of the role of cargo-exerted forces in axonal transport

“…Cytoplasmic viscosity measurements that do not include the protein/actin component can be as small as 0.06 Poise (Haak et al, 1976). However, viscosity measurements which look at the total cytoplasmic viscosity (actin + fluid) can be orders of magnitude higher (Keller et al, 2003). Using data from (Keller et al, 2003), we estimate the viscosity to be about 6 Poise (or 0.6 Pa•s).…”

“…However, viscosity measurements which look at the total cytoplasmic viscosity (actin + fluid) can be orders of magnitude higher (Keller et al, 2003). Using data from (Keller et al, 2003), we estimate the viscosity to be about 6 Poise (or 0.6 Pa•s).…”

Variation in Carbon Nanotube Polymer Composite Conductivity from the Effects of Processing, Dispersion, Aging and Sample Size

“…This phenomenon is analogous to the bundling of biological filaments, and is well understood there. 31 To further our understanding, we introduce here a mechanical parameter, the "persistence length l p ." It is given by 32 where is the bending modulus of the filament, k b is the Boltzman factor, and T is the absolute temperature.…”

Mathematics of cell motility: have we got its number?

“…is an interesting mathematical problem. Interesting novel theory of dynamics of 'active' actin gel is suggested in [115] Finally, let us mention that the actin network exhibit viscous, as well as elastic behavior [49].…”