Enzymatic heterogeneity of bovine retinal pigment epithelial cells in vivo and in vitro.
BACKGROUND
The retinal pigment epithelium (RPE) contains a variety of enzymes that are involved in the metabolism of the neural retina. It has been shown that the photoreceptor densities display regional variations. We aimed to find out whether the enzymes in the RPE also display regional differences.


METHODS
Various enzymes were localized in RPE cells in situ and in cultured RPE cells. RPE cells of the entire tapetal region of adult and fetal bovine eyes were examined. The following enzymes were studied: Activities of aminopeptidases A and M, dipeptidylpeptidases I and II, and gamma-glutamyltranspeptidase were localized by histochemistry. Alkaline phosphatase, dipeptidylpeptidase IV, and cathepsin B were studied by histochemistry and immunocytochemistry. In addition, activities of two enzymes were localized in one cell.


RESULTS
The distribution pattern of the enzymatic activities showed no marked regional differences. In contrast, pronounced cell-to-cell variability in the activities was detected for some of the enzymes tested. These intercellular differences were detected already in fetal retinae of early stages and persisted in RPE cultures.


CONCLUSIONS
The heterogeneous distribution of enzymatic activities in RPE cells appears not to be caused exclusively by stimuli from the neural retina and from the choroid, because heterogeneity starts in the early fetal period and persists in culture.
Anatomisches Institut der Eberhard-Karls-Universität, Tübingen, Germany. eleonore.froehlich@anatu.uni-tuebingen.de
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Fröhlich
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Klessen
D000469:Alkaline Phosphatase / Q000378:metabolism; D000626:Aminopeptidases / Q000378:metabolism; D000818:Animals; D018826:CD13 Antigens / Q000378:metabolism; D002401:Cathepsin B / Q000378:metabolism; D002417:Cattle; D002478:Cells, Cultured; D004152:Dipeptidyl-Peptidases and Tripeptidyl-Peptidases / Q000378:metabolism; D004798:Enzymes / Q000378:metabolism*; D005333:Fetus; D043384:Glutamyl Aminopeptidase; D006651:Histocytochemistry; D007124:Immunoenzyme Techniques; D010857:Pigment Epithelium of Eye / Q000166:cytology / Q000201:enzymology*; D014018:Tissue Distribution; D005723:gamma-Glutamyltransferase / Q000378:metabolism
D004798:Enzymes; D005723:gamma-Glutamyltransferase; D000469:Alkaline Phosphatase; D000626:Aminopeptidases; D018826:CD13 Antigens; D043384:Glutamyl Aminopeptidase; D004152:Dipeptidyl-Peptidases and Tripeptidyl-Peptidases; D002401:Cathepsin B