The regulation of ATP release from the urothelium by adenosine and transepithelial potential

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 degrees C. Results Distension-induced ATP release was decreased by adenosine (1-10 mu M) 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.