title: Intracellular adenosine inhibits IgE-dependent degranulation of human skin mast cells.
abstract: OBJECTIVE
  Adenosine (ADO) can enhance and inhibit mast cell degranulation. Potentiation of degranulation occurs at relatively low concentrations of ADO (10−6–10−5 M) through triggering of A3AR, whereas, inhibition occurs at higher concentrations of ADO reportedly through triggering of A2aAR. However, the discrepancy in the concentration of ADO that inhibits degranulation and that required to trigger ADORs suggests a different mechanism. The purpose of this study is to determine the mechanism by which ADO inhibits human mast cell degranulation.
  
  
  METHODS
  We compare the effectiveness of A2aAR specific antagonist ZM241385 and equilibrative nucleoside transporter inhibitors Dipyridamole and NBMPR in preventing ADO-mediated inhibition of FcεRI-induced degranulation of human skin mast cells (hSMCs). Western blotting is done to analyze the effect of ADO on FcεRI-induced Syk phosphorylation.
  
  
  RESULTS
  Dipyridamole and NBMPR completely and dose-dependently prevented ADO from inhibiting FcεRI-induced degranulation in all hSMC preparations. In contrast, ZM241385 at 10−5 M was effective in only 3 of 10 hSMC preparations. Moreover, NBMPR was effective even in those hSMC preparations not responsive to ZM241385. ADO inhibited degranulation induced by FcεRI crosslinking, but not that induced by complement component 5a (C5a), Substance P or calcium ionophore. Accordingly, ADO significantly attenuated FcεRI-induced phosphorylation of Syk at the critical activating tyrosine (Y525).
  
  
  CONCLUSIONS
  Blocking the influx of ADO, but not A2aAR signals, is necessary and sufficient to prevent ADO from inhibiting FcεRI-induced mast cell degranulation. Thus, ADO specifically inhibits FcεRI-induced degranulation of hSMCs primarily by an intracellular mechanism that requires its influx via equilibrative nucleoside transporter 1 (ENT1).
authors.forename: Gregorio
authors.initials: G
authors.lastname: Gomez
authors.forename: Vincent
authors.initials: V
authors.lastname: Nardone
authors.forename: Sahar
authors.initials: S
authors.lastname: Lotfi-Emran
authors.forename: Wei
authors.initials: W
authors.lastname: Zhao
authors.forename: Lawrence B
authors.initials: LB
authors.lastname: Schwartz
mesh_terms: D000241:Adenosine / Q000502:physiology* / Q000633:toxicity; D015550:Cell Degranulation / Q000276:immunology*; D002478:Cells, Cultured; D015536:Down-Regulation / Q000276:immunology*; D004357:Drug Synergism; D006801:Humans; D007073:Immunoglobulin E / Q000378:metabolism* / Q000502:physiology; D007424:Intracellular Fluid / Q000276:immunology / Q000378:metabolism; D008407:Mast Cells / Q000276:immunology / Q000378:metabolism*; D033703:Nucleoside Transport Proteins / Q000502:physiology; D017455:Receptors, IgE / Q000502:physiology; D015398:Signal Transduction / Q000276:immunology; D012867:Skin / Q000166:cytology / Q000276:immunology*
chemical_list: D033703:Nucleoside Transport Proteins; D017455:Receptors, IgE; D007073:Immunoglobulin E; D000241:Adenosine