A quantitative comparison of mechanoelectrical transduction in vestibular and auditory hair cells of neonatal mice.

Vestibular hair cells (VHCs) and cochlear outer hair cells (OHCs) of neonatal mice were stimulated by a fluid jet directed at their stereociliary bundles. Relations between the force exerted by the jet, bundle displacement, and the resulting transducer current were studied. The mean maximum transducer conductance in VHCs (2.6 nS) was about half that of the OHCs (5.5 nS), with the largest recorded values being 4.1 nS and 9.2 nS, respectively. In some OHCs activity of a single, 112 pS transducer channel was observed, allowing an estimate of the maximum number of channels: up to 36 in VHCs and 82 in OHCs, corresponding to about one transducer channel per tip link. The VHC bundles required about 330 nm of tip displacement to activate 90% of the maximum transducer conductance, compared to 150 nm for the OHC bundles. This corresponded to 2 deg of rotation about their pivots for both, due to the greater length of the VHC bundles. The VHC bundles' translational stiffness was one-seventh of that of the OHCs. Conversion to rotational stiffness almost abolished this difference. Rotation of the hair bundle rather than translation determines the gating of the transducer channels, independent of bundle height or origin of the cells.