Photo-induced irreversible shortening and swelling of isolated cochlear outer hair cells

Living outer hair cells were irradiated under conditions of fluorescent microscopy (epi-illumination through the objective) with UVR (waveband 340-380 nm), blue light (waveband 450-490 nm) or green light (waveband 515-560 nm) in the intracellular presence or absence of the fluorescent dyes fura-2 or 2',7'-bis-(carboxyethyl) 5-(and 6-)carboxyfluorescein (BCECF). In response to UVR with or without intracellular fura-2 and to blue light in the presence of BCECF (irradiation intensities of 2-12 x 10(5) W/m2), the cells shortened and swelled within 15-30 s, accompanied by the formation of numerous cytoplasmic granulations. The cellular reactions were significantly delayed to 3 min by the addition of 1 mM of the radical scavengers p-phenylenediamine or n-propyl gallate. This protection suggests that free radicals, produced under UVR or under blue light irradiation in the presence of the sensitizer BCECF, are possible causative agents of this cell damage. The response of the photo-damaged cells, namely shortening and increase in volume, resembled the characteristics of hair cells exposed to an hypo-osmotic shock. This suggests that structural alterations of the cytoplasmic membrane and the sub-membrane cortex occurred under photo-irradiation, and that these structures can be implicated in the maintenance of the elongated cylindrical shape of the outer hair cells, possibly by maintaining intracellular hyperosmolarity.