Escape of cargo from morphological traps in cytoskeletal networks

Intracellular transport of particles often consists of two phases - an active, molecular motor-driven phase along cytoskeletal filaments, and a passive, diffusive transport phase in the cytoplasm, with a stochastic rate of switching between the two phases. An interesting feature results when cytoskeletal filaments form aster-like traps, in which motors along different filaments arrive to a common point. Escape of cargo from such traps takes place by diffusion in the cytoplasm until a particle finds itself outside of the advective basin of attraction of a trap. To calculate the mean time for this escape, we constructed a one-dimensional model that consists of two layers: the advective layer (AL) - representing filaments, and a diffusive layer (DL) - representing the cytoplasm. The velocity field in the AL contains an attracting fixed point - representing the trap. A particle escapes the basin of attraction of a trap when it reaches the absorbing boundaries in the DL. Remarkably, the biophysical parameters are such that escape from basin of attraction of a trap is a rare event. The results are very sensitive to the placement of the trap within its basin of attraction and also display a non-trivial dependence on the initial position of the cargo.