Abstract:

The present study considers the issue of symmetry in relative hair bundle motion. The stereocilia on in vitro chick cochlear hair cells were viewed in profile, stimulated by an oscillating water jet, and observed under stroboscopic illumination. The angular deflection of the tallest hair was set to either 10, 15, or 20 deg. The angular displacements for the tallest and shortest hairs were measured in the excitatory and inhibitory directions relative to the rest position. Motion of the tallest hair was approximately symmetric for each stimulus magnitude, while short hair motion was greater in the excitatory than inhibitory direction (p<0.01). Moreover, short hair angular displacement with respect to the tall hair was greater in the excitatory direction (p<0.01), but equal in the inhibitory direction (p>0.01). These results suggested that stereocilia linkages were more analogous to strings than springs, in that they transmitted tension but collapsed under compression. Also, breakage of tip links in low calcium reduced relative motion between the tallest and shortest hairs, suggesting that motion in low calcium media was unchanged for the inhibitory direction, but dramatically reduced for excitatory displacements. [Work supported by NIDCD and NOHR.]