Accumulating evidence shows that the epithelial cells in urinary bladder (urothelium) serve as a sensory organ in micturition and/or in nociception pathway by releasing ATP in response to mechanical and/or chemical stimuli. Here, we compared the effects of capsaicin, acetylcholine, and prostaglandin E(2) receptor EP1 agonist (ONO-DI-004) on the urothelial ATP release in primary cultured mouse urothelial cells in low Ca(2+) medium. All of these chemicals induced a gradual ATP release from urothelium, implying that the downstream Ca(2+) release from endoplasmic reticulum could trigger the ATP release. Consistent with this suggestion, blockade of inositol 1,4,5-triphosphate receptor reduced the distention-induced ATP release from urothelial tissues. The distention-induced ATP release was not affected by tetrodotoxin. However, an increase in extracellular Ca(2+) diminished both chemical- and distention-induced ATP release from urothelium. Thus raising the extracellular Ca(2+) concentration was found to inhibit stimulation-evoked ATP urothelial release.