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 apic al end of the basilar papilla were maintained in culture medium and or iented so that the sensory hair bundles were viewed in profile. A wate r-jet was used to stimulate the hair bundle and stroboscopic illuminat ion allowed slow motion viewing of sensory hair motion at the bundle e dges. Motion of the tallest stereocilium in the bundle was set to a cr iterion angular deflection and the excursion of the shortest stereocil ium was measured. These measurements were made in a sample of hair cel ls maintained in culture medium containing either near normal levels o f calcium or very low calcium levels supplemented with EGTA. In low ca lcium the angular deflection of the shortest hair was significantly re duced from that observed in normal media. The resting inward tilt of t he hairs in the bundle, however, did not change. Scanning electron mic roscopy verified an almost complete destruction of tip links after exp osure to low calcium. These results suggest that tip links contribute significantly to the relative motion of stereocilia and exhibit the me chanical properties of a relatively stiff linkage. (C) 1998 Elsevier S cience B.V. All rights reserved.