Removal of urothelium affects bladder contractility and release of ATP but not release of NO in rat urinary bladder

Mechanotransduction in the urothelium: ATP signalling and mechanoreceptors

The urothelium, which covers the inner surface of the bladder, is continuously exposed to a complex physical environment where it is stimulated by, and responds to, a wide range of mechanical cues. Mechanically activated ion channels endow the urothelium with functioning in the conversion of mechanical stimuli into biochemical events that influence the surface of the urothelium itself as well as suburothelial tissues, including afferent nerve fibres, interstitial cells of Cajal and detrusor smooth muscle cells, to ensure normal urinary function during the cycle of filling and voiding. However, under prolonged and abnormal loading conditions, the urothelial sensory system can become maladaptive, leading to the development of bladder dysfunction. In this review, we summarize developments in the understanding of urothelial mechanotransduction from two perspectives: first, with regard to the functions of urothelial mechanotransduction, particularly stretch-mediated ATP signalling and the regulation of urothelial surface area; and secondly, with regard to the mechanoreceptors present in the urothelium, primarily transient receptor potential channels and mechanosensitive Piezo channels, and the potential pathophysiological role of these channels in the bladder. A more thorough understanding of urothelial mechanotransduction function may inspire the development of new therapeutic strategies for lower urinary tract diseases.

Urothelium removal does not impact mucosal activity in response to muscarinic or adrenergic receptor stimulation

The inner lining of the urinary bladder (urothelium and lamina propria, or bladder mucosa) has an important role as a tissue barrier between stored urine and the underlying smooth muscle, as well as in the modulation and regulation of bladder contractility. However, the individual influence of the apical urothelial layer on the contractile activity of this tissue is uncertain. The aim of this experiment was to identify the contractile activity of the lamina propria after removal of the urothelium. Several methods were used to mechanically disrupt the urothelium, including dabbing the tissue with a paper towel, longitudinal swipes with a cotton bud, or a longitudinal scrape with the edge of a scalpel. Hematoxylin-eosin staining was utilized to determine the level of removal of the apical urothelial cells. Spontaneous contractile activity was measured in organ baths, and responses to the agonists carbachol and isoprenaline were obtained. Three longitudinal swipes with a cotton bud was found to be the optimal method to remove the majority of the urothelium without damaging the lamina propria. Upon removal of the urothelium, the spontaneous activity of the tissue was unaltered. Similarly, responses to carbachol (1 µM) and isoprenaline (1 µM) were not affected after removal of the urothelium. The urothelium can be effectively removed without damaging the lamina propria. This apical tissue layer is not responsible for mediating the increases to spontaneous phasic activity or tonic contractions of the bladder mucosa (urothelium with lamina propria) when muscarinic or adrenergic receptors are stimulated. This research presents the lamina propria as the important cell layer mediating the overall contractile activity of the bladder wall.

The nitric oxide-cyclic guanosine monophosphate pathway inhibits the bladder ATP release in response to a physiological or pathological stimulus

The release of ATP from the epithelium of the urinary bladder (urothelium) in response to mechanical/chemical stimuli contributes to the visceral sensation in the micturition reflex. The nitric oxide (NO)-mediated induction of cyclic guanosine monophosphate (cGMP) has been detected in urothelial cells and may inhibit the micturition reflex. However, the function of the NO-cGMP pathway in the regulation of urothelial ATP release remains poorly understood in contrast to its effects on smooth muscles or primary afferent nerves. Therefore, we investigated the relevance of the NO-cGMP pathway to ATP release on the mucosal side in the present study. The administration of l-arginine (NO precursor) or NOC 12 (NO donor) significantly reduced ATP release to the mucosal side at a physiologically normal urine storage pressure (5 cmH2 O). L-NAME (NO synthase inhibitor) significantly increased the distention-induced release of ATP. The phosphodiesterase-5 inhibitor, sildenafil, which increases cGMP levels, inhibited distention-induced ATP release. Furthermore, sildenafil significantly reduced ATP release in response to the administration of lipopolysaccharide. These results suggest that the NO-cGMP pathway inhibited urothelial ATP release during the storage phase under both physiological and pathological conditions.

ATP shows more potential as a urinary biomarker than acetylcholine and PGE2 , but its concentration in urine is not a simple function of dilution

AIMS

To determine whether the amount of ATP, prostaglandin E₂ (PGE₂ ), and acetylcholine (ACh) in voided urine are influenced enough by that released within the lower urinary tract (LUT) for them to be useful biomarkers of bladder function.

METHODS

Participants without LUT symptoms collected total urine voids at 15, 30, 60, and 120 min (20 males/23 females) and 240 min (18 males/26 females) following the previous void. Aliquots of urine were immediately frozen at -20°C and later used to measure ATP (luciferin-luciferase), PGE₂ (enzyme-linked immunosorbent assay), ACh (mass spectrometry), creatinine (colorimetric), and lactose dehydrogenase (colorimetric).

RESULTS

The amount of ATP in voided urine correlated strongly with the rate of urine production, suggesting that the majority, if not all, the ATP in voided urine has an LUT, and likely bladder, origin. In contrast, there appeared to be no significant net LUTs release of creatinine or ACh into the urine. PGE₂ was intermediate with an LUT component that increased with urine production rate and contributed about 25% of the total at 1 ml/min in women but a smaller fraction in men.

CONCLUSION

Whereas the majority of the ATP measured within the voided urine originates in the LUT, ACh reflects that extracted from the plasma in the kidneys and PGE₂ is a mixture of both sources. ATP has the most potential as a biomarker of benign bladder disorders. Expressing urinary ATP concentration relative to creatinine concentration is questioned in light of these results.

Voiding Dysfunction in Old Male Rats Associated With Enlarged Prostate and Irregular Afferent-Triggered Reflex Responses

Purpose

This study was conducted to evaluate the hypothesis that an enlarged prostate in old rats may lead to complications associated with voiding dysfunction involving ionotropic P2X2/3-type purinergic receptors

Methods

Intact animals were divided into male young (MYR; 8–10 weeks old) and male old (MOR; 20 months old) rats. The animals underwent simultaneous detrusor electromyography (EMG) and suprapubic cystometry (CMG) under urethane anesthesia. Immunofluorescence techniques were used to evaluate prostatic autonomic innervation and P2X3R expression in bladder urothelial cells. The functional role of P2X3R was characterized by intramuscular application of AF-353, a selective P2X2/3R antagonist.

Results

The prostate index significantly increased in MOR, suggestive of an enlarged prostate affecting micturition patterns. Significant EMG and CMG differences were found between MYR and MOR. Higher immunoreactivity for P2X2/3R in the urothelial layer and for prostatic neurofilaments was seen in MOR. Systemic inhibition of P2X2/3R had minimal effects on MYR responsiveness, but improved voiding function in MOR with a marked decrease of intravesical pressure and bladder contractile responses.

Conclusions

The data support the hypothesis that an enlarged prostate in MOR may contribute to voiding dysfunction involving activation of P2X2/3R, which enhances a prostate-bladder reflex. This reflex may increase bladder afferent transmission and activation of increased prostate innervation, leading to voiding dysfunction.

The Urothelium: Life in a Liquid Environment

The urothelium, which lines the renal pelvis, ureters, urinary bladder, and proximal urethra, forms a high-resistance but adaptable barrier that surveils its mechanochemical environment and communicates changes to underlying tissues including afferent nerve fibers and the smooth muscle. The goal of this review is to summarize new insights into urothelial biology and function that have occurred in the past decade. After familiarizing the reader with key aspects of urothelial histology, we describe new insights into urothelial development and regeneration. This is followed by an extended discussion of urothelial barrier function, including information about the roles of the glycocalyx, ion and water transport, tight junctions, and the cellular and tissue shape changes and other adaptations that accompany expansion and contraction of the lower urinary tract. We also explore evidence that the urothelium can alter the water and solute composition of urine during normal physiology and in response to overdistension. We complete the review by providing an overview of our current knowledge about the urothelial environment, discussing the sensor and transducer functions of the urothelium, exploring the role of circadian rhythms in urothelial gene expression, and describing novel research tools that are likely to further advance our understanding of urothelial biology.

Modulatory effects of intravesical P2X2/3 purinergic receptor inhibition on lower urinary tract electromyographic properties and voiding function of female rats with moderate or severe spinal cord injury

OBJECTIVES

To evaluate the role that intravesical P2X2/3 purinergic receptors (P2X2/3Rs) play in early and advanced neurogenic lower urinary tract (LUT) dysfunction after contusion spinal cord injury (SCI) in female rats.

MATERIALS AND METHODS

Female Sprague-Dawley rats received a thoracic Th8/Th9 spinal cord contusion with either force of 100 kDy (cN); moderate) or 150 kDy (cN; severe); Sham rats had no injury. Evaluations on urethane-anesthetised rats were conducted at either 2 or 4 weeks after SCI. LUT electrical signals and changes in bladder pressure were simultaneously recorded using cystometry and a set of custom-made flexible microelectrodes, before and after intravesical application of the P2X2/3R antagonist AF-353 (10 μM), to determine the contribution of P2X2/3R-mediated LUT modulation.

RESULTS

Severe SCI significantly increased bladder contraction frequency, and reduced both bladder pressure amplitude and intraluminal-pressure high-frequency oscillations (IPHFO). Intravesical P2X2/3R inhibition did not modify bladder pressure or IPHFO in the Sham and moderate-SCI rats, although did increase the intercontractile interval (ICI). At 2 weeks after SCI, the Sham and moderate-SCI rats had significant LUT electromyographic activity during voiding, with a noticeable reduction in LUT electrical signals seen at 4 weeks after SCI. Intravesical inhibition of P2X2/3R increased the ICI in the Sham and moderate-SCI rats at both time-points, but had no effect on rats with severe SCI. The external urethral sphincter (EUS) showed strong and P2X2/3R-independent electrical signals in the Sham and moderate-SCI rats in the early SCI stage. At 4 weeks after SCI, the responsiveness of the EUS was significantly attenuated, independently of SCI intensity.

CONCLUSIONS

This study shows that electrophysiological properties of the LUT are progressively impaired depending on SCI intensity and that intravesical P2X2/3R inhibition can attenuate electrical activity in the neurogenic LUT at early, but not at semi-chronic SCI. This translational study should be useful for planning clinical evaluations.

Fiber type-specific afferent nerve activity induced by transient contractions of rat bladder smooth muscle in pathological states

Bladder smooth muscle shows spontaneous phasic contractions, which undergo a variety of abnormal changes depending on pathological conditions. How abnormal contractions affect the activity of bladder afferent nerves remains to be fully tested. In this study, we examined the relationship between transient increases in bladder pressure, representing transient contraction of bladder smooth muscle, and spiking patterns of bladder afferent fibers of the L6 dorsal root, in rat pathological models. All recordings were performed at a bladder pressure of approximately 10 cmH₂O by maintaining the degree of bladder filling. In the cyclophosphamide-induced model, both Aδ and C fibers showed increased sensitivity to transient bladder pressure increases. In the prostaglandin E2-induced model, Aδ fibers, but not C fibers, specifically showed overexcitation that was time-locked with transient bladder pressure increases. These fiber type-specific changes in nerve spike patterns may underlie the symptoms of urinary bladder diseases.

Changes in Adenosine Triphosphate and Nitric Oxide in the Urothelium of Patients with Benign Prostatic Hyperplasia and Detrusor Underactivity

PURPOSE

We investigated changes in the levels of adenosine triphosphate and nitric oxide in the urothelium of men with detrusor underactivity and benign prostatic hyperplasia.

MATERIALS AND METHODS

We prospectively enrolled in study 30 men who planned to undergo surgical treatment for benign prostatic hyperplasia. The 15 patients with a bladder contractility index less than 100 were assigned to the detrusor underactivity group while the 15 with a bladder contractility index more than 100 were assigned to the no detrusor underactivity group. Bladder mucosal specimens were collected at surgical prostate resection, and adenosine triphosphate and endothelial nitric oxide synthase were analyzed in these specimens. The levels of adenosine triphosphate and endothelial nitric oxide synthase were compared between the 2 groups. The correlation of urodynamic parameters with adenosine triphosphate and endothelial nitric oxide synthase was assessed in all patients.

RESULTS

Mean ± SEM endothelial nitric oxide synthase did not significantly differ between the detrusor underactivity and no underactivity groups (3.393 ± 0.969 vs 1.941 ± 0.377 IU/ml, p = 0.247). However, the mean level of adenosine triphosphate in the detrusor underactivity group was significantly lower than in the no detrusor underactivity group (1.289 ± 0.320 vs 9.262 ± 3.285 pmol, p = 0.011). In addition, in all patients adenosine triphosphate positively correlated with the bladder contractility index (r = 0.478, p = 0.018) and with detrusor pressure on maximal flow (r = 0.411, p = 0.046).

CONCLUSIONS

Adenosine triphosphate was significantly decreased in the urothelium in men with detrusor underactivity and benign prostatic hyperplasia, reflecting the change in detrusor function.

Octodon degus, a new model to study the agonist and plexus-induced response in the urinary bladder

Urinary bladder function consists in the storage and controlled voiding of urine. Translational studies require animal models that match human characteristics, such as Octodon degus, a diurnal rodent. This study aims to characterize the contractility of the detrusor muscle and the morphology and code of the vesical plexus from O. degus. Body temperature was measured by an intra-abdominal sensor, the contractility of detrusor strips was evaluated by isometric tension recording, and the vesical plexus was studied by electrical field stimulation (EFS) and immunofluorescence. The animals showed a diurnal chronotype as judged from core temperature. The myogenic contractile response of the detrusor muscle to increasing doses of KCl reached its maximum (31.04 mN/mm²) at 60 mM. In the case of cumulative dose-response of bethanecol, the maximum response (37.42 mN/mm²) was reached at 3.2 × 10^-4 M. The response to ATP was clearly smaller (3.8 mN/mm²). The pharmacological dissection of the EFS-induced contraction identified ACh and sensory fibers as the main contributors to this response. The neurons of the vesical plexus were located mainly in the trigone area, grouped in big and small ganglia. Out of them, 48.1 % of the neurons were nitrergic and 62.7 % cholinergic. Our results show functional and morphological similarities between the urinary bladder of O. degus and that of humans.

Mucosal modulation of contractility in bladder strips from normal and overactive rat models and the effect of botulinum toxin A on overactive bladder strips

AIMS

To investigate the local, regulatory role of the mucosa on bladder strip contractility from normal and overactive bladders and to examine the effect of botulinum toxin A (BoNT-A).

METHODS

Bladder strips from spontaneously hyperactive rat (SHR) or normal rats (Sprague Dawley, SD) were dissected for myography as intact or mucosa-free preparations. Spontaneous, neurogenic and agonist-evoked contractions were investigated. SHR strips were incubated in BoNT-A (3 h) to assess effects on contractility.

RESULTS

Spontaneous contraction amplitude, force-integral or frequency were not significantly different in SHR mucosa-free strips compared with intacts. In contrast, spontaneous contraction amplitude and force-integral were smaller in SD mucosa-free strips than in intacts; frequency was not affected by the mucosa. Frequency of spontaneous contractions in SHR strips was significantly greater than in SD strips. Neurogenic contractions in mucosa-free SHR and SD strips at higher frequencies were smaller than in intact strips. The mucosa did not affect carbachol-evoked contractions in intact versus mucosa-free strips from SHR or SD bladders. BoNT-A reduced spontaneous contractions in SHR intact strips; this trend was also observed in mucosa-free strips but was not significant. Neurogenic and carbachol-evoked contractions were reduced by BoNT-A in mucosa-free but not intact strips. Depolarisation-induced contractions were smaller in BoNT-A-treated mucosa-free strips.

CONCLUSIONS

The mucosal layer positively modulates spontaneous contractions in strips from normal SD but not overactive SHR bladder strips. The novel finding of BoNT-A reduction of contractions in SHR mucosa-free strips indicates actions on the detrusor, independent of its classical action on neuronal SNARE complexes.

The Role of the Mucosa in Normal and Abnormal Bladder Function

The internal face of the detrusor smooth muscle wall of the urinary bladder is covered by a mucosa, separating muscle from the hostile environment of urine. However, the mucosa is more than a very low permeability structure and offers a sensory function that monitors the extent of bladder filling and composition of the urine. The mucosa may be considered as a single functional structure and comprises a tight epithelial layer under which is a basement membrane and lamina propria. The latter region itself is a complex of afferent nerves, blood vessels, interstitial cells and in some species including human beings a muscularis mucosae. Stress on the bladder wall through physical or chemical stressors elicits release of chemicals, such as ATP, acetylcholine, prostaglandins and nitric oxide that modulate the activity of either afferent nerves or the muscular components of the bladder wall. The release and responses are graded so that the mucosa forms a dynamic sensory structure, and there is evidence that the gain of this system is increased in pathologies such as overactive bladder and bladder pain syndrome. This system therefore potentially provides a number of drug targets against these conditions, once a number of fundamental questions are answered. These include how is mediator release regulated; what are the intermediate roles of interstitial cells that surround afferent nerves and blood vessels; and what is the mode of communication between urothelium and muscle - by diffusion of mediators or by cell-to-cell communication?

A1 Adenosine Receptor-Mediated Inhibition of Parasympathetic Neuromuscular Transmission in Human and Murine Urinary Bladder

The potential role of A1 adenosine receptors in modulating neuromuscular transmission in the detrusor muscle of the urinary bladder has been tested in human and murine preparations with the intent to determine the viability of using adenosine receptor agonists as adjuncts to treat overactive bladder. In human detrusor muscle preparations, contractile responses to electrical field stimulation were inhibited by the selective A1 adenosine receptor agonists 2-chloro-N(6)-cyclopentyladenosine, N(6)-cyclopentyladenosine (CPA), and adenosine (rank order of potency: 2-chloro-N(6)-cyclopentyladenosine > CPA > adenosine). Pretreatment with 8-cyclopentyl-3-[3-[[4(fluorosulphonyl)benzoyl]oxy]propyl]-1-propylxanthine, an irreversible A1 antagonist, blocked the effects of CPA, thus confirming the role of A1 receptors in human detrusor preparations. In murine detrusor muscle preparations, contractions evoked by electrical field stimulation were reduced by CPA or adenosine. Amplitudes of the P2X purinoceptor-mediated excitatory junctional potentials (EJPs) recorded with intracellular microelectrodes were reduced in amplitude by CPA and adenosine with no effect on the spontaneous EJP amplitudes, confirming the prejunctional action of these agents. 8-Cyclopentyltheophylline, a selective A1 receptor antagonist, reversed the effects of CPA on EJP amplitudes with no effect of spontaneous EJPs, confirming the role of A1 receptors in mediating these effects.

Receptors involved in the modulation of guinea pig urinary bladder motility by prostaglandin D2

BACKGROUND AND PURPOSE

We have described a urothelium-dependent release of PGD2 -like activity which had inhibitory effects on the motility of guinea pig urinary bladder. Here, we have pharmacologically characterized the receptors involved and localized the sites of PGD2 formation and of its receptors.

EXPERIMENTAL APPROACH

In the presence of selective DP and TP receptor antagonists alone or combined, PGD2 was applied to urothelium-denuded diclofenac-treated urinary bladder strips mounted in organ baths. Antibodies against PGD2 synthase and DP1 receptors were used with Western blots and for histochemistry.

KEY RESULTS

PGD2 inhibited nerve stimulation -induced contractions in strips of guinea pig urinary bladder with estimated pIC50 of 7.55 ± 0.15 (n = 13), an effect blocked by the DP1 receptor antagonist BW-A868C. After blockade of DP1 receptors, PGD2 enhanced the contractions, an effect abolished by the TP receptor antagonist SQ-29548. Histochemistry revealed strong immunoreactivity for PGD synthase in the urothelium/suburothelium with strongest reaction in the suburothelium. Immunoreactive DP1 receptors were found in the smooth muscle of the bladder wall with a dominant localization to smooth muscle membranes.

CONCLUSIONS AND IMPLICATIONS

In guinea pig urinary bladder, the main effect of PGD2 is an inhibitory action via DP1 receptors localized to the smooth muscle, but an excitatory effect via TP receptors can also be evoked. The urothelium with its suburothelium might signal to the smooth muscle which is rich in PGD2 receptors of the DP1 type. The results are important for our understanding of regulation of bladder motility.

ATP release from freshly isolated guinea-pig bladder urothelial cells: a quantification and study of the mechanisms involved

OBJECTIVES

To quantify the amount of ATP released from freshly isolated bladder urothelial cells, study its control by intracellular and extracellular calcium and identify the pathways responsible for its release.

MATERIALS AND METHODS

Urothelial cells were isolated from male guinea-pig urinary bladders and stimulated to release ATP by imposition of drag forces by repeated pipetting. ATP was measured using a luciferin-luciferase assay and the effects of modifying internal and external calcium concentration and blockers of potential release pathways studied.

RESULTS

Freshly isolated guinea-pig urothelial cells released ATP at a mean (sem) rate of 1.9 (0.1) pmoles/mm(2) cell membrane, corresponding to about 700 pmoles/g of tissue, and about half [49 (6)%, n = 9) of the available cell ATP. This release was reduced to a mean (sem) of 0.46 (0.08) pmoles/mm(2) (160 pmoles/g) with 1.8 mm external calcium, and was increased about two-fold by increasing intracellular calcium. The release from umbrella cells was not significantly different from a mixed intermediate and basal cell population, suggesting that all three groups of cells release a similar amount of ATP per unit area. ATP release was reduced by ≈ 50% by agents that block pannexin and connexin hemichannels. It is suggested that the remainder may involve vesicular release.

CONCLUSIONS

A significant fraction of cellular ATP is released from isolated urothelial cells by imposing drag forces that cause minimal loss of cell viability. This release involves multiple release pathways, including hemichannels and vesicular release.

Signalling molecules in the urothelium

The urothelium was long considered to be a silent barrier protecting the body from the toxic effects of urine. However, today a number of dynamic abilities of the urothelium are well recognized, including its ability to act as a sensor of the intravesical environment. During recent years several pathways of these urothelial abilities have been proposed and a major part of these pathways includes release of signalling molecules. It is now evident that the urothelium represents only one part of the sensory web. Urinary bladder signalling is finely tuned machinery of signalling molecules, acting in autocrine and paracrine manner, and their receptors are specifically distributed among different types of cells in the urinary bladder. In the present review the current knowledge of the formation, release, and signalling effects of urothelial acetylcholine, ATP, adenosine, and nitric oxide in health and disease is discussed.

Cascade bioassay evidence for the existence of urothelium-derived inhibitory factor in Guinea pig urinary bladder

Our aim was to investigate whether guinea pig urothelium-derived bioactivities compatible with the existence of urothelium-derived inhibitory factor could be demonstrated by in vitro serial bioassay and whether purinergic P1 receptor agonists, nitric oxide, nitrite or prostaglandins might explain observed activities. In a cascade superfusion system, urothelium-denuded guinea pig ureters were used as bioassay tissues, recording their spontaneous rhythmic contractions in presence of scopolamine. Urothelium-intact or -denuded guinea pig urinary bladders were used as donor tissues, stimulated by intermittent application of carbachol before or during the nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME), the adenosine/P1 nucleoside receptor antagonist 8-(p-sulfophenyl)theophylline (8-PST) or the cyclo-oxygenase inhibitor diclofenac infused to bath donor and bioassay tissues. The spontaneous contractions of bioassay ureters were unaltered by application of carbachol 1-5 µM in the presence of scopolamine 5-30 µM. When carbachol was applied over the urothelium-denuded bladder, the assay ureter contraction rate was unaltered. Introducing carbachol over the everted urothelium-intact bladder significantly inhibited the contraction frequency of the assay ureter, suggesting the transfer of an inhibitory activity from the bladder to the assay ureter. The transmissible inhibitory activity was not markedly antagonized by L-NAME, 8-PST or diclofenac, while L-NAME nearly abolished nitrite release from the urothelium-intact bladder preparations. We suggest that urothelium-derived inhibitory factor is a transmissible entity over a significant distance as demonstrated in this novel cascade superfusion assay and seems less likely to be nitric oxide, nitrite, an adenosine receptor agonist or subject to inhibition by administration of a cyclo-oxygenase inhibitor.

NTPDase3 and ecto-5'-nucleotidase/CD73 are differentially expressed during mouse bladder cancer progression

According to the World Health Organization, bladder cancer is the seventh most common cancer among men in the world. The current treatments for this malignancy are not efficient to prevent the recurrence and progression of tumors. Then, researches continue looking for better therapeutic targets which can end up in new and more efficient treatments. One of the recent findings was the identification that the purinergic system was involved in bladder tumorigenesis. The ectonucleotidases, mainly ecto-5'-nucleotidase/CD73 have been revealed as new players in cancer progression and malignity. In this work, we investigated the NTPDase3 and ecto-5'-nucleotidase/CD73 expression in cancer progression in vivo. Bladder tumor was induced in mice by the addition of 0.05 % of N-butyl-N-(hydroxybutyl)-nitrosamine (BBN) in the drinking water for 4, 8, 12, 18, and 24 weeks. After this period, mice bladders were removed for histopathology analysis and immunofluorescence assays. The bladder of animals which has received BBN had alterations, mainly inflammation, in initial times of tumor induction. After 18 weeks, mice's bladder has developed histological alterations similar to human transitional cell carcinoma. The cancerous urothelium, from mice that received BBN for 18 and 24 weeks, presented a weak immunostaining to NTPDase3, in contrast to an increased expression of ecto-5'-nucleotidase/CD73. The altered expression of NTPDase3 and ecto-5'-nucleotidase/CD73 presented herein adds further evidence to support the idea that alterations in ectonucleotidases are involved in bladder tumorigenesis and reinforce the ecto-5'-nucleotidase/CD73 as a future biomarker and/or a target for pharmacological therapy of bladder cancer.

The purinergic component of human bladder smooth muscle cells' proliferation and contraction under physiological stretch

OBJECTIVE

To investigate whether cyclic stretch induces proliferation and contraction of human smooth muscle cells (HBSMCs), mediated by P2X purinoceptor 1 and 2 and the signal transduction mechanisms of this process.

METHODS

HBSMCs were seeded on silicone membrane and stretched under varying parameters; (equibiaxial elongation: 2.5%, 5%, 10%, 15%, 20%, 25%), (Frequency: 0.05Hz, 0.1Hz, 0.2Hz, 0.5Hz, 1Hz). 5-Bromo-2-deoxyuridine assay was employed for proliferative studies. Contractility of the cells was determined using collagen gel contraction assay. After optimal physiological stretch was established; P2X1 and P2X2 were analyzed by real time polymerase chain reaction and Western Blot. Specificity of purinoceptors was maintained by employing specific inhibitors; (NF023 for P2X1, and A317491for P2X2), in some experiments.

RESULTS

Optimum proliferation and contractility were observed at 5% and 10% equibiaxial stretching respectively, applied at a frequency of 0.1Hz; At 5% stretch, proliferation increased from 0.837±0.026 (control) to 1.462±0.023%, p<0.05. Mean contraction at 10% stretching increased from 31.7±2.3%, (control) to 78.28 ±1.45%, p< 0.05. Expression of P2X1 and P2X2 was upregulated after application of stretch. Inhibition had effects on proliferation (1.232±0.051, p<0.05 NF023) and (1.302±0.021, p<0.05 A314791) while contractility was markedly reduced (68.24±2.31, p<0.05 NF023) and (73.2±2.87, p<0.05 A314791). These findings shows that mechanical stretch can promote magnitude-dependent proliferative and contractile modulation of HBSMCs in vitro, and P2X1 and 2 are at least partially responsible in this process.

Urinary ATP may be a dynamic biomarker of detrusor overactivity in women with overactive bladder syndrome

BACKGROUND

Nowadays, there is a considerable bulk of evidence showing that ATP has a prominent role in the regulation of human urinary bladder function and in the pathophysiology of detrusor overactivity. ATP mediates nonadrenergic-noncholinergic detrusor contractions in overactive bladders. In vitro studies have demonstrated that uroepithelial cells and cholinergic nerves from overactive human bladder samples (OAB) release more ATP than controls. Here, we compared the urinary ATP concentration in samples collected non-invasively from OAB women with detrusor overactivity and age-matched controls.

METHODS

Patients with neurologic diseases, history of malignancy, urinary tract infections or renal impairment (creatinine clearance <70 ml/min) were excluded. All patients completed a 3-day voiding diary, a 24 h urine collection and blood sampling to evaluate creatinine clearance. Urine samples collected during voluntary voids were immediately freeze-preserved for ATP determination by the luciferin-luciferase bioluminescence assay; for comparison purposes, samples were also tested for urinary nerve growth factor (NGF) by ELISA.

RESULTS

The urinary content of ATP, but not of NGF, normalized to patients' urine creatinine levels (ATP/Cr) or urinary volume (ATP.Vol) were significantly (P<0.05) higher in OAB women with detrusor overactivity (n = 34) than in healthy controls (n = 30). Significant differences between the two groups were still observed by boosting urinary ATP/Cr content after water intake, but these were not detected for NGF/Cr. In OAB patients, urinary ATP/Cr levels correlated inversely with mean voided volumes determined in a 3-day voiding diary.

CONCLUSION

A high area under the receiver operator characteristics (ROC) curve (0.741; 95% CI 0.62-0.86; P<0.001) is consistent with urinary ATP/Cr being a highly sensitive dynamic biomarker for assessing detrusor overactivity in women with OAB syndrome.

Diabetic plasticity of non-adrenergic non-cholinergic and P2X-mediated rat bladder contractions

We investigated the plasticity effects of diabetes mellitus and diuresis on the non-adrenergic non-cholinergic (NANC) and purinergic (P2X-type) contractile responses in longitudinal rat bladder strips. Female Sprague-Dawley rats received streptozotocin to induce diabetes, or sucrose in water to induce diuresis as a control condition for polyuria. Experiments were carried out at four weeks after treatments, using bladders from non-treated rats as control. Urinary bladder strips were electrically stimulated throughout the experiments to generate neurally evoked contractions (NEC). In all cases, P2X-mediated purinergic contractions were evaluated at the beginning and end of the stimulations with α,β-methylene-adenosine triphosphate (α,βMeATP). The NANC responses were assessed by using two independent protocols. First, cholinergic receptors were activated with carbachol (CCh), followed by inhibition of the muscarinic component with atropine. In the second protocol, the application order for CCh and atropine was reversed. The NANC response, unmasked with the application of atropine, and the P2X purinergic contractions were analyzed. NANC contractions in diabetic bladder strips are more resistant to the desensitizing effects caused by activation of cholinergic receptors. In early stages of experimental diabetes, NANC responses in diabetic strips are less sensitive to functional inhibition mediated by the cholinergic activation. However, P2X-mediated purinergic contractions are more sensitive to desensitization in diabetic or diuretic bladders. For instance preventing muscarinic receptor activation with atropine does not counteract the desensitization of purinergic contractions in either diabetic or diuretic strips. We suggest that diabetes may induce a plasticity of the NANC and P2X-mediated bladder contractile responses. The first one may be associated with diabetic neuropathic damage to bladder nerves, while impaired P2X purinergic contractions might be associated with detrusor hypertrophy observed in diabetic and diuretic strips.

Urothelial signaling

The urothelium, which lines the inner surface of the renal pelvis, the ureters, and the urinary bladder, not only forms a high-resistance barrier to ion, solute and water flux, and pathogens, but also functions as an integral part of a sensory web which receives, amplifies, and transmits information about its external milieu. Urothelial cells have the ability to sense changes in their extracellular environment, and respond to chemical, mechanical and thermal stimuli by releasing various factors such as ATP, nitric oxide, and acetylcholine. They express a variety of receptors and ion channels, including P2X3 purinergic receptors, nicotinic and muscarinic receptors, and TRP channels, which all have been implicated in urothelial-neuronal interactions, and involved in signals that via components in the underlying lamina propria, such as interstitial cells, can be amplified and conveyed to nerves, detrusor muscle cells, and ultimately the central nervous system. The specialized anatomy of the urothelium and underlying structures, and the possible communication mechanisms from urothelial cells to various cell types within the bladder wall are described. Changes in the urothelium/lamina propria ("mucosa") produced by different bladder disorders are discussed, as well as the mucosa as a target for therapeutic interventions.

How does the urothelium affect bladder function in health and disease? ICI-RS 2011

The urothelium is a multifunctional tissue that not only acts as a barrier between the vesical contents of the lower urinary tract and the underlying tissues but also acts as a sensory organ by transducing physical and chemical stresses to the attendant afferent nervous system and underlying smooth muscle. This review will consider the nature of the stresses that the urothelium can transduce; the transmitters that mediate the transduction process; and how lower urinary pathologies, including overactive bladder syndrome, painful bladder syndrome and bacterial infections, are associated with alterations to this sensory system. In particular, the role of muscarinic receptors and the TRPV channels system will be discussed in this context. The urothelium also influences the contractile state of detrusor smooth muscle, both through modifying its contractility and the extent of spontaneous activity; potential pathways are discussed. The potential role that the urothelium may play in bladder underactivity is introduced, as well as potential biomarkers for the condition that may cross the urothelium to the urine. Finally, consideration is given to vesical administration of therapeutic agents that influence urinary tract function and how the properties of the urothelium may determine the effectiveness of this mode of delivery.

Plasticity of non-adrenergic non-cholinergic bladder contractions in rats after chronic spinal cord injury

The purpose of this study was to examine the pharmacologic plasticity of cholinergic, non-adrenergic non-cholinergic (NANC), and purinergic contractions in neurogenic bladder strips from spinal cord injured (SCI) rats. Bladder strips were harvested from female rats three to four weeks after T(9)-T(10) spinal cord transection. The strips were electrically stimulated using two experimental protocols to compare the contribution of muscarinic and NANC/purinergic contractions in the presence and the absence of carbachol or muscarine. The endpoints of the study were: (1) percent NANC contraction that was unmasked by the muscarinic antagonist 4-DAMP, and (2) P2X purinergic contraction that was evoked by α,β-methylene ATP. NANC contraction accounted for 78.5% of the neurally evoked contraction in SCI bladders. When SCI bladder strips were treated with carbachol (10 μM) prior to 4-DAMP (500 nM), the percent NANC contraction decreased dramatically to only 13.1% of the neurally evoked contraction (P=0.041). This was accompanied by a substantial decrease in α,β-methylene ATP evoked P2X contraction, and desensitization of purinergic receptors (the ratio of subsequent over initial P2X contraction decreased from 97.2% to 42.1%, P=0.0017). Sequential activation of the cholinergic receptors with carbachol (or with muscarine in neurally intact bladders) and unmasking of the NANC response with 4-DAMP switched the neurally evoked bladder contraction from predominantly NANC to predominantly cholinergic. We conclude that activation of muscarinic receptors (with carbachol or muscarine) blocks NANC and purinergic contractions in neurally intact or in SCI rat bladders. The carbachol-induced inhibition of the NANC contraction is expressed more in SCI bladders compared to neurally intact bladders. Along with receptor plasticity, this change in bladder function may involve P2X-independent mechanisms.

Porcine bladder urothelial, myofibroblast, and detrusor muscle cells: characterization and ATP release

ATP is released from the bladder mucosa in response to stretch, but the cell types responsible are unclear. Our aim was to isolate and characterize individual populations of urothelial, myofibroblast, and detrusor muscle cells in culture, and to examine agonist-stimulated ATP release. Using female pig bladders, urothelial cells were isolated from bladder mucosa following trypsin-digestion of the luminal surface. The underlying myofibroblast layer was dissected, minced, digested, and cultured until confluent (10–14 days). A similar protocol was used for muscle cells. Cultures were used for immunocytochemical staining and/or ATP release investigations. In urothelial cultures, immunoreactivity was present for the cytokeratin marker AE1/AE3 but not the contractile protein α-smooth muscle actin (α-SMA) or the cytoskeletal filament vimentin. Neither myofibroblast nor muscle cell cultures stained for AE1/AE3. Myofibroblast cultures partially stained for α-SMA, whereas muscle cultures were 100% stained. Both myofibroblast and muscle stained for vimentin, however, they were morphologically distinct. Ultrastructural studies verified that the suburothelial layer of pig bladder contained abundant myofibroblasts, characterized by high densities of rough endoplasmic reticulum. Baseline ATP release was higher in urothelial and myofibroblast cultures, compared with muscle. ATP release was significantly stimulated by stretch in all three cell populations. Only urothelial cells released ATP in response to acid, and only muscle cells were stimulated by capsaicin. Tachykinins had no effect on ATP release. In conclusion, we have established a method for culture of three cell populations from porcine bladder, a well-known human bladder model, and shown that these are distinct morphologically, immunologically, and pharmacologically.

Antimuscarinics suppress adenosine triphosphate and prostaglandin E2 release from urothelium with potential improvement in detrusor overactivity in rats with cerebral infarction

PURPOSE

Antimuscarinics improve detrusor overactivity. We evaluated the effects and action mechanisms of imidafenacin (Kyorin Pharmaceutical, Tokyo, Japan), a novel therapeutic agent for overactive bladder with antimuscarinic activity, on mediator release from urothelium and detrusor overactivity induced by cerebral infarction.

MATERIALS AND METHODS

Bladder hydrodistention was achieved by intravesical infusion of Krebs solution. Bladder adenosine triphosphate and prostaglandin E(2) were measured in the presence and absence of anticholinergics using luciferin-luciferase assay and enzyme-linked immunoassay, respectively. Cerebral infarction was induced in rats by occluding the left middle cerebral artery. The effects of intravenous imidafenacin on bladder function were examined using cystometry in rats with cerebral infarction and in those pretreated with resiniferatoxin.

RESULTS

Increased intravesical adenosine triphosphate and prostaglandin E(2) were shown by induced distention of isolated rat bladders. Imidafenacin and darifenacin (Kemprotec, Middlesbrough, United Kingdom) significantly suppressed the increases in adenosine triphosphate and prostaglandin E(2). Decreased bladder capacity was observed in rats with cerebral infarction. Detrusor overactivity was suppressed with a minimum intravenous dose of 0.001 mg/kg imidafenacin. The effects of imidafenacin were not noted in rats pretreated with resiniferatoxin.

CONCLUSIONS

Results support the hypothesis or suggest that imidafenacin improves cerebral infarction induced detrusor overactivity by suppressing peripheral C-fibers. This effect is thought to be associated with suppression of the release of adenosine triphosphate and prostaglandin E(2) from the urothelium.

Expression and distribution of ectonucleotidases in mouse urinary bladder

Background

Normal urinary bladder function requires bidirectional molecular communication between urothelium, detrusor smooth muscle and sensory neurons and one of the key mediators involved in this intercellular signaling is ATP. Ectonucleotidases dephosphorylate nucleotides and thus regulate ligand exposure to P2X and P2Y purinergic receptors. Little is known about the role of these enzymes in mammalian bladder despite substantial literature linking bladder diseases to aberrant purinergic signaling. We therefore examined the expression and distribution of ectonucleotidases in the mouse bladder since mice offer the advantage of straightforward genetic modification for future studies.

Principal Findings

RT-PCR demonstrated that eight members of the ectonucleoside triphosphate diphosphohydrolase (NTPD) family, as well as 5′-nucleotidase (NT5E) are expressed in mouse bladder. NTPD1, NTPD2, NTPD3, NTPD8 and NT5E all catalyze extracellular nucleotide dephosphorylation and in concert achieve stepwise conversion of extracellular ATP to adenosine. Immunofluorescent localization with confocal microscopy revealed NTPD1 in endothelium of blood vessels in the lamina propria and in detrusor smooth muscle cells, while NTPD2 was expressed in cells localized to a region of the lamina propria adjacent to detrusor and surrounding muscle bundles in the detrusor. NTPD3 was urothelial-specific, occurring on membranes of intermediate and basal epithelial cells but did not appear to be present in umbrella cells. Immunoblotting confirmed NTPD8 protein in bladder and immunofluorescence suggested a primary localization to the urothelium. NT5E was present exclusively in detrusor smooth muscle in a pattern complementary with that of NTPD1 suggesting a mechanism for providing adenosine to P1 receptors on the surface of myocytes.

Conclusions

Ectonucleotidases exhibit highly cell-specific expression patterns in bladder and therefore likely act in a coordinated manner to regulate ligand availability to purinergic receptors. This is the first study to determine the expression and location of ectonucleotidases within the mammalian urinary bladder.