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RICHARD W. YOUNG, DEAN BOK; Autoradiographic Studies on the Metabolism of the Retinal Pigment Epithelium. Invest. Ophthalmol. Vis. Sci. 1970;9(7):524-536.
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The metabolism of the retinal pigment epithelium in the frog has been studied by autoradiography after the injection of tritiated cytidine, leucine + phenylalanine, vitajnin A, and galactose. The results show that the mature pigment epithelium is metabolically active. RNA in the nucleus and cytoplasm undergoes continual replacement. New RNA is produced in the nucleus. Much of it remains there, but some of it flows out into the cytoplasm. Protein synthesis occurs continually, taking place with approximately equal intensity in the nucleus and cytoplasm. Some of the protein moves into the cytoplasmic processes surrounding the visual cell outer segments. The cell's content of vitamin A also undergoes renewal. Vitamin A is taken up from the circulation and concentrated in cytoplasmic oil droplets. The metabolism of galactose is predominantly confined to the cytoplasm. Galactose is initially concentrated in the Golgi complex, but is soon released from that organelle. Much of the radioactive product is secreted into the oil droplets, where it turns over rapidly. Radioactive material incorporated into the rod outer segment discs following the injection of galactose-Hs can be identified in phagosomes in the pigment epithelium after the labeled discs have been shed from the outer segments.
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