Recovery of hair cell function after damage induced by gentamicin in organ culture of rat vestibular maculae

Here, we report the functional and morphological evidence of hair cell recovery after damages induced by gentamicin (GM) inultured explants of rat vestibular maculae. We evaluated mechano-electrical transduction (MET) function in hair cells, by measuring Ca2+ responses in the explants with fura-2 when hair bundles were stimulated. After the MET testing, hair bundles were observed in high resolution by scanning electron microscopy, or by fluorescence microscopy after staining with phalloidin-FITC (fluorescent isothiocyanate). In the control culture, the number of hair bundles on the explants gradually decreased, and the percentage of explants showing Ca2+ responses decreased and disappeared after 17 days in culture. Following GM (1-2 mM) treatment, most of the hair bundles were eliminated initially, but the hair bundles gradually increased in number during culture. Short hair bundle-like structures emerged in the areas where hair bundles had been completely lost. Consistent with the morphological observations, Ca2+ responses disappeared after GM treatment, and they gradually recovered to a peak 13-17 days after treatment and were even induced at 17 days or more in culture. Furthermore, cells accumulated FMI-43, a dye permeable through the MET channel, when Ca2+ responses recovered after GM treatment. Application of steroid hormone increased the percentage of explants showing MET activity, and enhanced the recovery of MET after GM treatment. We investigated Ki-67 immunoreactivity to detect cell proliferation and TUNEL staining to detect apoptotic cell death, Ki-67 immunoreactivity was negative after GM treatment, however TUNEL staining was positive and the positivity was GM dose dependent. Therefore, this functional recovery of transduction activity was not owing to the proliferation of hair cells but was likely the self-repair of the hair bundle. (c) 2006 Elsevier B.V. All rights reserved.