Extracellular Ca2+ regulates the stimulus-elicited ATP release from urothelium.

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.

The involvement of urothelial alpha1A adrenergic receptor in controlling the micturition reflex.

The current study was undertaken in an attempt to characterize the functional properties of urothelial alpha1A adrenergic receptors, especially in modulating the micturition reflex. The expression of alpha1A receptors in rat bladder was analyzed by immunohistochemistry and Western blotting. As a functional study, we obtained continuous infusion cystometrograms in conscious rats using noradrenaline (NA) and subtype selective alpha1 adrenergic receptor antagonists, tamsulosin (alpha1A/alpha1D selective) and silodosin (alpha1A superselective). Alpha1A receptors were immunohistochemically detected in rat urothelium. Intravesical infusion of NA (60 microM) significantly shortened the intercontraction interval (ICI). Pretreatment with tamsulosin at a dose of 0.4 microg/kg i.v. abolished intravesical NA infusioninduced reduction of ICI. Neither intravesical infusion of tamsulosin (20 microM) nor that of silodosin (0.2 microM) significantly altered ICI. After intravesical infusion of silodosin, intravesical NA infusion did not affect ICI. Urothelial alpha1A receptors might modulate bladder afferent activity under pathophysiological conditions with augmented concentrations of NA in blood or urine.

Urothelium EP1 receptor facilitates the micturition reflex in mice.

We investigated the presence of EP1 receptor in the urothelium and its role in micturition reflex by examining the effect of intravesical administration of prostaglandin E(2) (PGE2), an EP1 agonist (ONO-DI-004), acetic acid, and capsaicin. Age-matched EP1-KO mice and C57BL/6 wild-type (WT) mice were used. Western blots and standard immunohistochemical procedures were performed. Cystometrygram (CMG) was performed without anesthesia in a restraining cage. ATP release from the cultured urothelium cells was performed using luciferin-luciferase luminometry. The EP1 receptor was found to be present in the urothelium. In WT mice, PGE2 infusion shortened the intercontraction interval (ICI) in a dose-dependent fashion; however, it did not alter the ICI in EP1-KO mice. The EP1 agonist significantly shortened the ICI in WT mice, but not in EP1-KO mice. Acetic acid and capsaicin shortened the ICI in both WT mice and EP1-KO mice. EP1 agonist, PGE2 and capsaicin provoked ATP release from cultured urothelial cells. These results suggest that EP1 receptor was present in bladder urothelium, and could be activated by PGE2 to release ATP. EP1 receptor in urothelium might be important for reflex voiding in pathological conditions.

Activation of alpha1D adrenergic receptors in the rat urothelium facilitates the micturition reflex.

PURPOSE: Previous studies have revealed that the activation of alpha(1) adrenergic receptors in urothelial cells releases neurotransmitters. We determined if alpha(1D) adrenergic receptors are expressed in the urothelium of the rat bladder and if inhibition of these receptors affects reflex voiding. MATERIALS AND METHODS: Female Wistar rats were used in the experiments. Receptor expression was evaluated by Western blot. The effects of receptor activation were studied using cystometrograms, measurement of adenosine triphosphate concentrations in the bladder lumen and afferent nerve recording. The alpha(1D) antagonist naftopidil (0.75 to 1.66 mg/kg) was administered intravenously into the external jugular vein. RESULTS: The expression of alpha(1D) adrenergic receptors was detected in urothelial tissue with Western blot and immunohistochemistry. The alpha(1D) receptor antagonist naftopidil prolonged the intercontraction interval during continuous infusion cystometrograms in conscious rats (143% of the control value) and suppressed the excitatory effect of intravesical infusion of acetic acid (0.1%) on the intercontraction interval (220%). Naftopidil inhibited the bladder afferent nerve activity induced by bladder distention (32.0%) and acetic acid infusion (30.4%), and decreased adenosine triphosphate levels in the bladder perfusate during bladder distention (36.6%). CONCLUSIONS: Endogenous catecholamines appear to act on alpha(1D) receptors in the urothelium to facilitate mechanosensitive bladder afferent nerve activity and reflex voiding.

Decidualization induces the expression and activation of an extracellular protease neuropsin in mouse uterus.

Uterine decidualization is accompanied by the remodeling of the cell-matrix and cell-cell interactions around the endometrial stromal cells to allow an appropriate invasion of trophoblasts. This remodeling is thought to require the proteolysis of extracellular matrix proteins or cell adhesion molecules; however, the molecular mechanism remains poorly understood. In this study, decidualization induced the expression and activation of an extracellular serine protease neuropsin in the mouse uterus. Although nonpregnant uteri contained little neuropsin, the protein content and enzymatic activity increased markedly and peaked at the midgestational period in pregnant uteri. Neuropsin expression and activity was also upregulated in artificially induced deciduomata but not in nondecidualized pseudopregnant uteri. Neuropsin is the first extracellular protease to show the evident induction of expression and activity by decidualization and might contribute to the remodeling of extracellular components after decidualization.