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C Friedman, X Zhang, AM Laties, CH Mitchell; Ecto-Nucleotidases on RPE Cells: a Potential Source of Extracellular Adenosine . Invest. Ophthalmol. Vis. Sci. 2002;43(13):900.
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Purpose: Stimulation of adenosine receptors on RPE cells can modify phagocytosis and may influence transport across the cells. The source of adenosine capable of stimulating these receptors is unknown, but in other cells, released ATP is converted to adenosine through a series of extracellular enzymes. As RPE cells can release ATP, this study investigates the presence and activity of ecto-nucleotidases in RPE cells. Methods: A polyclonal antibody to CD-39 (ecto-apyrase; ATP to ADP to AMP) was tested in mouse retina. Ecto-5’nucleotidase (AMP to adenosine) activity was investigated with the lead precipitate reaction on the ARPE-19 line of cultured human RPE cells and albino rat sections. RT-PCR was performed on RNA from ARPE-19 cells with primers for CD39 and CD73 (ecto-5’nucleotidase). Results: CD39 was identified immunohistochemically on both apical and basolateral membranes of mouse RPE. Activity of 5’nucleotidase was detected on non-permeabilized ARPE-19 cells, consistent with extracellular activity from ecto-5’nucleotidase. Activity of 5’nucleotidase was also detected throughout sections of rat RPE cells, although it was not possible to distinguish between an apical and basolateral location. Preliminary RT-PCR data suggests that mRNA transcripts for both CD39 and CD73 are present in ARPE-19 cells. Conclusion: These results suggest that RPE cells possess the ecto-enzymes capable of converting released ATP into adenosine. This could serve as a source of extracellular adenosine capable of stimulating receptors.
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