Abstract: Objective To clarify which adenosine receptor subtype is the most powerful one on controlling retinal pigment epithelial cell (RPE) binding adenosine, and what is its function in RPE. Methods Total mRNA was isolated, and membrane protein was extracted from in vitro cultured human ARPE-19 cells. For all four kinds of adenosine receptors, ARA1, ARA2A, ARA2B and ARA3, their gene expressions were tested by real-time PCR while their molecules in the membrane protein were detected by Western blot assay. To check the influence of each adenosine receptor subtype on ARPE-19 cell binging ability to adenosine the cultured cells were divided into five groups, named A-E. A group was set up as untreated control, while, groups B-E were separately treated by ARA1 agonist DPCPX (50 nmol / L), ARA2A agonist SCH58261 (100 nmol/L), ARA2B agonist MRS1754 (100 nmol/L) or ARA3 agonist MRS1220 (5 μmol/L). H3-adenosine a radioactive ligand binding assay was performed and the maximum binding capacities (Bmax) were calculated in groups A-E of ARPE-19 cells. Then, ARPE-19 cells were all treated by the combination of TNF-α and IFN-γ but with or without CCPA (100 nmol/L), an ARA1 agonist. MCP-1, IP-10, IL-6, IL-10 and TGF-β in their mediums were determined by ELISA. Results Either mRNA expression or membrane localization of ARA1, ARA2A, ARA2B and ARA3 were verified by realtime PCR and Western blot assay respectively. For A-E groups of ARPE-19 cells the Bmax of adenosine binding were (2.04± 0.31), (0.44±0.06), (1.82±0.28), (2.01±0.42) and (2.06±0.44) fmol respectively; and which were statistically decreased in group B than those of all other groups (P＜0.01). Compared with control RPE, the contents of IL-6, MCP-1 and IP-10 were decreased after treatment with CCPA, and the content of IL-10 increased in RPE group (P＜0.01). There was no significant difference in TGF- β content between the two groups. Conclusion APRE-19 cells predominantly use ARA1 to absorb adenosine, and the activation of ARA1 in ARPE-19 cells inhibits its IL-6, MCP-1, and IP-10 production, which have potentially immunosuppressive effects to APRE-19 cells.

Key words: receptors, purinergic P1, retinol pigment epithelium, binding, function；A1 subtype