Mechanical stimulation of individual stereocilia of living cochlear hair cells by atomic force microscopy

This paper describes the investigation of elastical properties and imaging of living cochlear hair bundles of inner (IHC) and outer hair cells (OHC) o n the level of individual stereocilia. A custom-made AFM-setup was used, al lowing to scan the mechano-sensitive structures of the inner ear under dire ct control of an upright differential interference contrast (DIC) microscop e with a water-immersion objective. Scanning electron microscopy (SEM) imag es of the identical hair bundles obtained after AFM investigation demonstra ted that forces up to 1.5 nanonewton (nN) did not cause obvious damage of t he surface morphology of the stereocilia. These are the first images of hai r bundles of living sensory cells of the organ of Corti by AFM, They displa y the tips of individual stereocilia and the typical V-shape of ciliary bun dles. Since line scans clearly show that slope and force interaction depend on the elastical properties of stereocilia, quantitative stiffness measure ments and stimulation of single transduction channels are suggested. (C) 20 00 Elsevier Science B.V. All rights reserved.