Electrically evoked motile responses of mammalian type I vestibular hair cells

Vestibular hair cells, type I and II, with membrane potentials around -64 mV were prepared from guinea pig ampullar cristae and maculae. In type I cells, current injection, application of voltage steps during membrane patch-clamping, or extracellular alternating current (ac) fields evoked fast length changes of 50 nm to 500 nm of the cell "neck." Mechanical responses were determined by computerized video techniques with contrast-enhanced digital image subtraction (DIS) and interpeak pixel counts (IPPC) or by double photodiode measurements. These techniques allowed spatial resolutions of 300 nm, 120 nm, and 50 nm, respectively. In contrast to measurements of high-frequency movements of auditory outer hair cells (OHCs), the mechanical responses of type I VHCs were restricted to low frequencies below 85 Hz. In addition to recently reported slow motility of VHCs, the present results suggest that fast mechanical VHC responses could significantly influence macular and cupular mechanics. Isometric and isotonic variants are discussed. The observed frequency maxima gap between VHCs and OHCs is suggested to contribute to a clear separation of the auditory and the vestibular sensory modality.