title: Degradation of extracellular ATP by the retinal pigment epithelium.
abstract: Stimulation of ATP or adenosine receptors causes important physiological changes in retinal pigment epithelial (RPE) cells that may influence their relationship to the adjacent photoreceptors. While RPE cells have been shown to release ATP, the regulation of extracellular ATP levels and the production of dephosphorylated purines is not clear. This study examined the degradation of ATP by RPE cells and the physiological effects of the adenosine diphosphate (ADP) that result. ATP was readily broken down by both cultured human ARPE-19 cells and the apical membrane of fresh bovine RPE cells. The compounds ARL67156 and betagamma-mATP inhibited this degradation in both cell types. RT-PCR analysis of ARPE-19 cells found mRNA message for multiple extracellular degradative enzymes; ectonucleotide pyrophosphatase/phosphodiesterase eNPP1, eNPP2, and eNPP3; the ectoATPase ectonucleoside triphosphate diphosphohydrolase NTPDase2, NTPDase3, and some message for NTPDase1. Considerable levels of ADP bathed RPE cells, consistent with a role for NTPDase2. ADP and ATP increased levels of intracellular Ca(2+). Both responses were inhibited by thapsigargin and P2Y(1) receptor inhibitor MRS 2179. Message for both P2Y(1) and P2Y(12) receptors was detected in ARPE-19 cells. These results suggest that extracellular degradation of ATP in subretinal space can result in the production of ADP. This ADP can stimulate P2Y receptors and augment Ca(2+) signaling in the RPE.
authors.affiliation: Dept. of Physiology, University of Pennsylvania, Philadelphia, PA 19104-6085, USA.
authors.forename: David
authors.initials: D
authors.lastname: Reigada
authors.forename: Wennan
authors.initials: W
authors.lastname: Lu
authors.forename: Xiulan
authors.initials: X
authors.lastname: Zhang
authors.forename: Constantin
authors.initials: C
authors.lastname: Friedman
authors.forename: Klara
authors.initials: K
authors.lastname: Pendrak
authors.forename: Alice
authors.initials: A
authors.lastname: McGlinn
authors.forename: Richard A
authors.initials: RA
authors.lastname: Stone
authors.forename: Alan M
authors.initials: AM
authors.lastname: Laties
authors.forename: Claire H
authors.initials: CH
authors.lastname: Mitchell
mesh_terms: D000244:Adenosine Diphosphate / Q000494:pharmacology; D000251:Adenosine Triphosphatases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000493:pharmacokinetics*; D000818:Animals; D015703:Antigens, CD / Q000235:genetics / Q000378:metabolism; D001081:Apyrase / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling / Q000502:physiology; D002417:Cattle; D002460:Cell Line; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005110:Extracellular Space / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic; D005956:Glucose-6-Phosphate Isomerase / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D006023:Glycoproteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D006801:Humans; D008565:Membrane Proteins / Q000378:metabolism; D009097:Multienzyme Complexes / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D043264:Phosphodiesterase I; D010727:Phosphoric Diester Hydrolases / Q000235:genetics / Q000378:metabolism*; D010857:Pigment Epithelium of Eye / Q000166:cytology / Q000201:enzymology*; D011687:Purines / Q000378:metabolism; D011755:Pyrophosphatases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D018048:Receptors, Purinergic P2 / Q000378:metabolism; D058472:Receptors, Purinergic P2Y1; D058925:Receptors, Purinergic P2Y12; D020133:Reverse Transcriptase Polymerase Chain Reaction; D000099189:Lysophospholipase D
chemical_list: D000244:Adenosine Diphosphate; D000251:Adenosine Triphosphatases; D000255:Adenosine Triphosphate; D015703:Antigens, CD; D001081:Apyrase; D002118:Calcium; D004791:Enzyme Inhibitors; D005956:Glucose-6-Phosphate Isomerase; D006023:Glycoproteins; D008565:Membrane Proteins; D009097:Multienzyme Complexes; D043264:Phosphodiesterase I; D010727:Phosphoric Diester Hydrolases; D011687:Purines; D011755:Pyrophosphatases; D018048:Receptors, Purinergic P2; D058472:Receptors, Purinergic P2Y1; D058925:Receptors, Purinergic P2Y12; D000099189:Lysophospholipase D; C427944:ENPP3 protein, human; C546382:P2RY1 protein, human; C548576:P2RY12 protein, human; C065962:ectonucleotide pyrophosphatase phosphodiesterase 1; C027201:ectoATPase; C067869:CD39 antigen