PROTEIN-SYNTHESIS AND SECRETION BY CULTURED RETINAL-PIGMENT EPITHELIA

Protein synthesis and secretion by post-natal sheep and calf retinal p igment epithelial (RPE) cells was investigated following labelling of choroidal pieces, isolated RPE cells and RPE cells in tissue culture w ith L-[U-C-14] leucine. We show that RPE cells secrete a specific set of proteins that includes retinol binding protein (REP) and transthyre tin (TTR), which are both involved in retinol transport in blood. Usin g a two-chambered culture system we show that protein secretion by the post-natal RPE cells occurs predominantly across the apical pole of t he cells, i.e., across the surface of the cells which, in vivo, faces the retina. In agreement with results of others using foetal RPE cells (Ong, D.E., Davis, J.T., O'Day, W.T. and Bok, D. (1994) Biochemistry 33, 1835-1842) we show that REP and, to a lesser extent, TTR are also secreted predominantly across the apical pole of the cell. We have dev eloped a cell culture model for the RPE that may be used as an in vitr o model for studying transport across the blood-retinal barrier.