  Molecular motor proteins serve as an essential component of intracellular
transport by generating forces to haul cargoes along cytoskeletal filaments.
Two species of motors that are directed oppositely (e.g. kinesin, dynein) can
be attached to the same cargo, which is known to produce bidirectional net
motion. Although previous work focuses on the motor number as the driving noise
source for switching, we propose an alternative mechanism: cargo diffusion. A
mean-field mathematical model of mechanical interactions of two populations of
molecular motors with cargo thermal fluctuations (diffusion) is presented to
study this phenomenon. The delayed response of a motor to fluctuations in the
cargo velocity is quantified, allowing for the reduction of the full model a
single "characteristic distance", a proxy for the net force on the cargo. The
system is then found to be metastable, with switching exclusively due to cargo
diffusion between distinct directional transport states. The time to switch
between these states is then investigated using a mean first passage time
analysis. The switching time is found to be non-monotonic in the drag of the
cargo, providing an experimental test of the theory.
