Low calcium abolishes tip links and alters relative stereocilia motion in chick cochlear hair cells.

The role of stereocilia tip links in controlling hair bundle motion on chick hair cells was examined in this study. Hair cells from the apical end of the basilar papilla were maintained in culture medium and oriented so that the sensory hair bundles were viewed in profile. A water-jet was used to stimulate the hair bundle and stroboscopic illumination allowed slow motion viewing of a sensory hair motion at the bundle edges. Motion of the tallest stereocilium in the bundle was set to a criterion angular deflection and the excursion of the shortest stereocilium was measured. These measurements were made in a sample of hair cells maintained in culture medium containing either near normal levels of calcium or very low calcium levels supplemented with EGTA. In low calcium the angular deflection of the shortest hair was significantly reduced from that observed in normal media. The resting inward tilt of the hairs in the bundle, however, did not change. Scanning electron microscopy verified an almost complete destruction of tip links after exposure to low calcium. These results suggest that tip links contribute significantly to the relative motion of stereocilia and exhibit the mechanical properties of a relatively stiff linkage.