Polarity of 11-cis retinal release from cultured retinal pigment epithelium

PURPOSE. Petal bovine retinal pigment epithelium (RPE) was grown on porous supports to investigate the polarity of 11-cis retinal (RAL) release from t hese cells and the influence that the interphotoreceptor retinoid-binding p rotein (IRBP) has on this process. METHODS. [H-3]all-trans retinol (ROL) was delivered to the basal surface of the cultured RPE by serum retinol-binding protein (RBP). Apo IRBP was adde d to either the apical or basal medium, or was absent from the incubation e ntirely. RESULTS. The greatest level of [H-3]11-cis RAL was detected in the apical m edium but only when apo IRBP was present there. When apo IRBP was present o nly in the basal medium, or was absent from the incubation entirely low lev els of [H-3]11-cis RAL were released apically and basally CONCLUSIONS. if 11-cis RAL release were constitutive, one would expect to f ind elevated levels of this retinoid in the apical and basal media in the a bsence of apo IRBP. Instead, the enhancement of [H-3]11-cis RAL release int o the apical, but not the basal, medium in the presence of apo IRBP suggest s that [H-3]11-cis RAL release is polarized and dependent on the presence o f apo IRBP. It is postulated, therefore, that a mechanism such as an IRBP m embrane receptor in the apical plasma membrane may be responsible for this polarity.