title: The regulation of ATP release from the urothelium by adenosine and transepithelial potential.
abstract: WHAT'S KNOWN ON THE SUBJECT? AND WHAT DOES THE STUDY ADD?: Stretch of the urothelium, as occurs during bladder filling, is associated with a release of ATP that is postulated to act as a sensory neurotransmitter. The regulation of ATP release is poorly understood and in particular if there is a feedback mechanism provided by ATP itself. Adenosine, a breakdown product of ATP, is a potent inhibitor of stretch-induced ATP release, acting through and A1 receptor; endogenous levels are about 0.6μM. Data are consistent with ATP release relying on the rise of intracellular Ca2+. Transepithelial potential also controls ATP release, also acting via an A1 receptor-dependent pathway.
  
  
  OBJECTIVE
  To test the hypothesis that distension-induced ATP release from the bladder urothelium is regulated by adenosine as well as changes to transurothelial potential (TEP). To examine the role of changes to intracellular [Ca(2+) ] in ATP release.
  
  
  METHODS
  Rabbit urothelium/suburothelium membranes were used in an Ussing chamber system. Distension was induced by fluid removal from the chamber bathing the serosal (basolateral) membrane face. The TEP and short-circuit current were measured. ATP was measured in samples aspirated from the serosal chamber by a luciferin-luciferase assay. Intracellular [Ca(2+) ] was measured in isolated urothelial cells using the fluorochrome Fura-2. All experiments were performed at 37°C.
  
  
  RESULTS
  Distension-induced ATP release was decreased by adenosine (1-10 μm) and enhanced by adenosine deaminase and A1- (but not A2-) receptor antagonists. Distension-induced ATP release was reduced by 2-APB, nifedipine and capsazepine; capsaicin induced ATP release in the absence of distension. ATP and capsaicin, but not adenosine, generated intracellular Ca(2+) transients; adenosine did not affect the ATP-generated Ca(2+) transient. ATP release was dependent on a finite transepithelial potential. Changes to TEP, in the absence of distension, generated ATP release that was in turn reduced by adenosine.
  
  
  CONCLUSIONS
  Adenosine exerts a powerful negative feedback control of ATP release from the urothelium via A1 receptor activation. Distension-induced ATP release may be mediated by a rise of the intracellular [Ca(2+) ]. Modulation of distension-induced ATP release by adenosine and TEP may have a common pathway.
authors.affiliation: Department of Pharmacology, University of Cambridge, Cambridge, UK.
authors.forename: Bryony M
authors.initials: BM
authors.lastname: Dunning-Davies
authors.forename: Christopher H
authors.initials: CH
authors.lastname: Fry
authors.forename: Dina
authors.initials: D
authors.lastname: Mansour
authors.forename: Douglas R
authors.initials: DR
authors.lastname: Ferguson
mesh_terms: D000241:Adenosine / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D005456:Fluorescent Dyes; D016257:Fura-2; D011817:Rabbits; D043682:Receptor, Adenosine A1 / Q000378:metabolism; D001743:Urinary Bladder / Q000378:metabolism*; D019459:Urothelium / Q000378:metabolism*
chemical_list: D005456:Fluorescent Dyes; D043682:Receptor, Adenosine A1; D000255:Adenosine Triphosphate; D000241:Adenosine; D002118:Calcium; D016257:Fura-2