Distribution and polarity of actin in the sensory hair cells of the chinchilla cochlea.

The distribution and polarity of actin in sensory hair cells of the chinchilla cochlea has been determined by decoration of actin filaments with myosin subfragment S1. Decorated actin filaments of the same polarity were present within the stereocilia above the cuticular plate. However the filaments in the rootlets and the thin filaments projecting laterally from the rootlets into the cuticular plate did not decorate with S1. Decorated actin filaments were present within the cuticular plate, and near the plasma-membrance filaments of opposite polarity were observed. In the cross-striated region at the base of the cuticular plate of inner hair cells, decorated filaments were present in the dense bands of the cross-striations but the thin filaments perpendicular to the dense bands were not decorated. These results are discussed with respect to the two mechanisms that have been suggested for actin-myosin mediated movement of the stereocilia of inner-ear sensory cells.