Mechanical fluctuations in saccular hair cells by optical techniques

Hair cells of the auditory and vestibular systems are capable of detecting sub-nanometer deflections due to vibrations. In certain species and under specific conditions, they are also known to spontaneously oscillate without external stimulation. Mechanical input is converted into electrical signals by mechanically gated ion channels that open upon the deflection of hair bundles located on top of the hair cell somae. We studied in vitro the mechanical fluctuations occurring inside of hair cells from the sacculus of the American bullfrog under different conditions. The hair cells were analyzed by wide field light microscopy, obtaining optical sections. Spatial distribution of light intensity was recorded, as a means of tracking movement of various sub-cellular structures. We observed hair cells during spontaneous oscillations of the hair bundle and under stimulation of the efferent nerves. These conditions were achieved by properly adjusting the immersion solutions and employing a suction electrode for neuronal activation. Prominent mechanical motion was registered in the lower area of the cell body, close to where the synaptic boutons from innervating neurons are located. This indicates the presence of active motility in the hair cell soma, which has not hitherto been reported.