DISTRIBUTION OF ACTIN AND TUBULIN IN OUTER HAIR-CELLS ISOLATED FROM DEVELOPING RAT COCHLEA - A QUANTITATIVE STUDY

In the organ of Corti, outer hair cells (OHCs) are sensory effecters r esponsible for the high sensitivity and sharp tuning of the cochlea, W hilst the distribution and organization of actin and tubulin in adult OHCs have been extensively studied, less is known about developing OHC s. In this study we use a quantitative cytometric approach on rat isol ated OHCs to measure the distribution of these cytoskeletal proteins f rom the first stages of development (postnatal day 5) to the adult sta ge, We report a general decrease in both actin and tubulin concentrati ons during OHC maturation, Actin first decreases in the apical domain, and then in the medio-basal domain, In the apical domain, this could be related to the physiological reduction in the number of stereocilia occurring during ciliogenesis, In the medio-basal domain, the decreas e, accompanied by a redistribution of actin toward the lateral wall, i s possibly related to the general reorganization of cytoplasmic organe lles, to the maturation of the cortical lattice, and to cell growth, T ubulin concentration decreases regularly in both the apical and the me dio-basal domains, This developmental change in tubulin concentration could be due to the regression of the kinocilium that occurs by the en d of ciliogenesis, and, as argued for actin, to the general reorganiza tion of cytoplasmic organelles, and to cell growth.