Spontaneous and electrically induced movements of ampullary kinocilia and stereovilli

In the transparent vestibular organ of young eels, isolated in toto, movements of individual kinocilia and hair bundles of the frontal ampulla were recorded by photodiodes and a video system. Flagella-like oscillations of kinocilia occurred spontaneously when preparations deteriorated and could be induced regularly in fresh preparations by pressing onto the tip of the cilium. Upon step-like electrical polarization of the epithelium hair bundles deflected in a tonic, pointer-like manner. When the apical membrane was hyperpolarized the hair bundles deflected towards the kinocilium (positive deflection) amounting to about 0.6 degrees when the polarization was made strong enough to cause saturating responses in the ampullary nerve. In response to sinusoidal voltage the amplitude of the hair bundle deflection declined by -4 dB/octave for frequencies above 1.3 Hz. When the kinocilium was disconnected from the bundle of stereovilli by transient reduction of divalent cations, voltage induced deflections occurred, of both the kinocilium and the stereovilli. Reducing the extracellular Ca-activity seemed to destabilize the electrically induced deflections; blocking the oxidative metabolism (CN-) had no effect. The induced deflections only disappeared upon chemical fixation by glutaraldehyde or treatment with triton X-100. Surface tension and electrostriction of the cell membrane are discussed as possible force generators.