Sulfate and galactose metabolism in differentiating ciliary body and iris epithelia: autoradiographic and ultrastructural studies.

Immature and adult rat eyes were bisected and incubated with 35-SO4 and 3-U-galactose in short-term pulse-chase experiments. Autoradiographs (ARG) of the tissue revealed that very little sulfate is incorporated by the peripheral neural retina, the pigment epithelia of the retina, ciliary body, or iris. The inner, inverted optic cup cells at the ora serrata, i.e., those that are undergoing differentiation into the unpigmented epithelium of the ciliary body, incorporate large amounts of 35-sulfate into "fixable" macromolecules. The sulfate label is chased from the apically located Golgi apparatus to the basal surface of these cells within one hour. Ultrastructurally, these cells are beginning to develop lateral and basal invaginations of the plasma membrane characteristic of the adult secretory epithelial cells. Electron microscopic ARG show label associated with the plasma membranes. The sulfated macro-molecules at this site appear to be glycolipids and glycoproteins rather than glycosaminoglycans. The preferential synthesis of these macromolecules and their placement at the cellular site of aqueous humor production suggests a role for these sulfated substances in establishing, and perhaps maintaining, that secretory process. 3-H-galactose was incorporated into "fixable" macromolecules to some degree by all the neuroepithelial cells. After chase incubation, ARG showed a high concentration of label in differentiated retinal pigment epithelium (RPE), but not in undiffenentiated peripheral RPE. Ciliary body unpigmented and pigment epithelium, and iris muscle cells incorporate galactose, but to a lesser degree than either RPE or corneal endothelial cells.