Enzymatic heterogeneity of bovine retinal pigment epithelial cells in vivoand in vitro

Background: The retinal pigment epithelium (RPE) contains a variety of enzy mes that are involved in the metabolism of the neural retina. It has been s hown that the photoreceptor densities display regional variations. We aimed to find out whether the enzymes in the RPE also display regional differenc es. Methods: Various enzymes were localized in RPE cells in situ and in cul tured RPE cells. RPE cells of the entire tapetal region of adult and fetal bovine eyes were examined. The following enzymes were studied: Activities o f aminopeptidases A and M, dipeptidylpeptidases I and II, and gamma -glutam yltranspeptidase were localized by histochemistry. Alkaline phosphatase, di peptidylpeptidase IV, and cathepsin B were studied by histochemistry and im munocytochemistry. In addition, activities of two enzymes were localized in one cell. Results: The distribution pattern of the enzymatic activities sh owed no marked regional differences. In contrast, pronounced cell-to-cell v ariability in the activities was detected for some of the enzymes tested. T hese intercellular differences were detected already in fetal retinae of ea rly stages and persisted in RPE cultures. Conclusion: The heterogeneous dis tribution of enzymatic activities in RPE cells appears not to be caused exc lusively by stimuli from the neural retina and from the choroid, because he terogeneity starts in the early fetal period and persists in culture.