Analytical Solution of a Model of Integrin-Cytoskeletal Interactions in Migrating Fibroblasts

(Received 12 August 1994, accepted in final form 6 December 1994)

Abstract
We demonstrate that an exact analytical solution can be constructed for an intracellular directed transport model of integrin developed by Schmidt et al. (1994). The model attempts to mimick the experimental observation that integrin is transported intermittently, by a combination of two-dimensional diffusion and cytoskeleton-mediated convective transport, towards the cell edge. In particular, the model assumes stochastic coupling and uncoupling of integrin molecules (described by first-order rate coefficients and ) to a cytoskeletal element moving at a fixed velocity V₀. Uncoupled integrins are assumed to undergo isotropic two dimensional diffusion with a diffusion coefficient D₀. We demonstrate for this model that, in the asymptotic limit of transport over large distances and long times, transport is described by parallel diffusion and convection processes with effective diffusivity and effective velocity , where is an equilibrium constant for decoupling. At shorter times, the mean-squared displacement cannot be described by superposing diffusion and convection; rather complicated transport arises from dynamical correlations associated with the coupled reaction, diffusion, and convection processes.