Active radial and transverse motile responses of outer hair cells in the organ of corti

In isolated outer hair cells (OHCs) electrically induced movements of high frequencies have been described. The experiments, however, gave no information whether fast OHC motility exists in situ. In the present report, we developed a technique to prepare viable half turn explants from the guinea-pig cochlea which could be kept as organ culture. Several video imaging methods and pixel-by-pixel, digital-image subtractions allowed simultaneous observations and quantitative measurements at video rates of 688 x 512 localizations of investigated segments of the organ of Corti (OC). When living cochlea explants were exposed to an electrical a.c. field, the OHCs in the OC followed this field by shortenings and elongations of their cell bodies and by radial movements of their cuticular plates (CP). This was accompanied by radial displacements of the hair bundles. In the apical turns video stroboscopy allowed recording of in situ movements of OHCs up to auditory frequencies. In all experiments motile responses were most prominent in the three rows of the OHCs. No or less pronounced passive motile responses could be observed at the tunnel of Corti (TC) and in the inner hair cells (IHCs). Mechanical decoupling of OHCs and IHCs at the TC resulted in a loss of IHC movements, whereas OHCs were uneffected. Motility was detectable in the presence of physiological salt solutions (300 mOsm/l) and in iso-osmolar mannitol or sorbitol solutions. The electrically induced motile responses were not suppressed in the presence of dinitrophenol or cytochalasin B. Thus, the present report shows active transverse and radial motile responses of OHCs in the OC, which are electro-mechanical in situ processes. The results indicate how outer hair cell electromotility may influence hearing when it occurs within the mechanical framework of the OC.