Synthesis and migration of ³H‐fucose‐labeled glycoproteins in the retinal pigment epithelium of albino rats, as visualized by radioautography

Abstract

3H-fucose was injected into the vitreous body of the eye(s) of 250-gm rats, which were then killed by means of an intracardiac perfusion with glutaraldehyde after intervals of 10 min, 1 and 4 hr, and 1 and 7 days. The eyes were removed and further fixed, and pieces of retina were processed for light and electron microscope radioautography. Light microscope radioautography showed that the pigment epithelial cells actively incorporated 3H-fucose label. The intensity of reaction peaked at 4 hr after injection of the label and then slowly declined. Quantitative electron microscope radioautography revealed that, at 10 min after 3H-fucose injection, over 70% of the label was localized to the Golgi apparatus, indicating that fucose residues are added to newly synthesized glycoproteins principally at this site. With time the proportion of label associated with the Golgi apparatus decreased, but that assigned to the infolded basal plasma membrane, the apical microvilli, and various apical lysosomes increased. These results indicate that in retinal pigment epithelial cells newly synthesized glycoproteins continuously migrate from the Golgi apparatus to lysosomes and to various regions of the plasma membrane. In this case, the membrane glycoproteins may play specific roles in receptor functions of the basal plasma membrane or phagocytic activities at the apical surface. Very little label migrated to Bruch's membrane, indicating either a very slow turnover or a paucity of fucose-containing glycoproteins at this site.

Synthesis of lens capsule and plasma membrane glycoproteins by lens epithelial cells and fibers in the rat

“…This suggests that fucose residues were added to the carbohydrate side chains of newly synthesized glycoproteins at this site, as has been documented in a large variety of other cell types (reviewed by Bennett, 1984;Farquhar, 19851, including other ocular cell types such as ciliary epithelial cells (Bennet and Haddad, 1986) and retinal pigment epithelial cells (Haddad and Bennett, 1987). The Golgi apparatus, as well as other organelles of the secretory pathway, tend to be less prominent in lens epithelial cells than in most other cell types (Kuwabara, 1975), but the present study suggests that they function in a similar manner.…”

“…With time after 3H-fucose injection, the plasma membranes of both the lens epithelial cells and the lens fibers became increasingly labeled, suggesting that newly synthesized glycoproteins had migrated from the Golgi apparatus to this site, a phenomenon now documented in a great variety of cell types (Bennett, 1984;Farquhar, 1985;Bennett and Haddad, 1986;Haddad and Bennett, 1987).…”

“…act. 14.6 Ci/mmol) with a technique previously described (Haddad and Bennett, 1987). The animals were killed at time intervals of 10 min; 1 and 4 hr; 1, 3,7, and 14 days; and 1, 4, 6, 10, 12, and 14.5 months after 3H-fucose injection by a 2-min intracardiac perfusion with saline followed by a 10-min perfusion with 3% glutaraldehyde in Sorensen's phosphate buffer.…”