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Keywords:

  • urothelium;
  • distension;
  • ATP release;
  • adenosine;
  • transepithelial potential

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.

Objectives

  • 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 [Ca2+] in ATP release.

Materials and 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 [Ca2+] 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 Ca2+ transients; adenosine did not affect the ATP-generated Ca2+ 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.

Conclusion

  • 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 [Ca2+].
  • Modulation of distension-induced ATP release by adenosine and TEP may have a common pathway.