Rod photoreceptors in the human retina synthesize and secrete interstitial retinol-binding protein.

3H-fucose has been used as a probe to identify the retinal cells responsible for the synthesis of the fucose-containing glycoprotein, IRBP. While all retinal cells utilize 3H-fucose, rod photoreceptors show the highest levels of incorporation. Rods, cones and some cells in the inner nuclear layer lose 75%, 11% and 14%, respectively, of their radioactivity during the chase incubation period. Radioactivity lost during the chase incubation period can be recovered from the incubation medium and characterized immunochemically as radiolabeled IRBP. While cones and cells of the inner nuclear layer (Muller's cells?) cannot be excluded as minor contributors, the major share of radioactivity lost from rods indicates that rod photoreceptors are principally responsible for the synthesis and secretion of IRBP.