Actin in cochlear hair cells-implications for stereocilia movement.

The distribution and polarity of actin in chinchilla cochlear hair cells was determined by decoration of actin filaments with myosin subfragment S1. Actin is present in the stereocilia above the cuticular plate and there are actin filaments randomly oriented within the cuticular plate. These results in chinchilla cochlear hair cells agree with the findings in the frog, guinea pig, and alligator lizard inner ears. In the cross-striated region at the base of the cuticular plate of inner hair cells there are actin filaments which label with S1. These decorated filaments appear closely associated with the dense bands but the thin filaments perpendicular to the dense bands appear unlabeled. The presence of actin filaments in this cross-striated region at the base of the cuticular plate supports a mechanism that has been suggested for actin-myosin mediated movement of stereocilia [10], which would cause the stereocilia of inner hair cells to fan out into the endolymph.