Urothelial function

Overactive Bladder and Cognitive Impairment: The American Urogynecologic Society and Pelvic Floor Disorders Research Foundation State-of-the-Science Conference Summary Report

IMPORTANCE

Overactive bladder (OAB) is prevalent in older adults in whom management is complicated by comorbidities and greater vulnerability to the cognitive effects of antimuscarinic medications.

OBJECTIVES

The aim of this study is to provide a comprehensive evidence-based summary of the 2021 State-of-the-Science (SOS) conference and a multidisciplinary expert literature review on OAB and cognitive impairment.

STUDY DESIGN

The American Urogynecologic Society and the Pelvic Floor Disorders Research Foundation convened a 3-day collaborative conference. Experts from multidisciplinary fields examined cognitive function, higher neural control of the OAB patient, risk factors for cognitive impairment in older patients, cognitive effects of antimuscarinic medications for OAB treatment, OAB phenotyping, conservative and advanced OAB therapies, and the need for a multidisciplinary approach to person-centered treatment. Translational topics included the blood-brain barrier, purine metabolome, mechanotransduction, and gene therapy for OAB targets.

RESULTS

Research surrounding OAB treatment efficacy in cognitively impaired individuals is limited. Short- and long-term outcomes regarding antimuscarinic effects on cognition are mixed; however, greater anticholinergic burden and duration of use influence risk. Oxybutynin is most consistently associated with negative cognitive effects in short-term, prospective studies. Although data are limited, beta-adrenergic agonists do not appear to confer the same cognitive risk.

CONCLUSIONS

The 2021 SOS summary report provides a comprehensive review of the fundamental, translational, and clinical research on OAB with emphasis on cognitive impairment risks to antimuscarinic medications. Duration of use and antimuscarinic type, specifically oxybutynin when examining OAB treatments, appears to have the most cognitive impact; however, conclusions are limited by the primarily cognitively intact population studied. Given current evidence, it appears prudent to minimize anticholinergic burden by emphasizing nonantimuscarinic therapeutic regimens in the older population and/or those with cognitive impairment.

The urothelium: a multi-faceted barrier against a harsh environment

All mucosal surfaces must deal with the challenge of exposure to the outside world. The urothelium is a highly specialized layer of stratified epithelial cells lining the inner surface of the urinary bladder, a gruelling environment involving significant stretch forces, osmotic and hydrostatic pressures, toxic substances, and microbial invasion. The urinary bladder plays an important barrier role and allows the accommodation and expulsion of large volumes of urine without permitting urine components to diffuse across. The urothelium is made up of three cell types, basal, intermediate, and umbrella cells, whose specialized functions aid in the bladder's mission. In this review, we summarize the recent insights into urothelial structure, function, development, regeneration, and in particular the role of umbrella cells in barrier formation and maintenance. We briefly review diseases which involve the bladder and discuss current human urothelial in vitro models as a complement to traditional animal studies.

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.

Pathophysiology of the underactive bladder

Underactive bladder (UAB), which has been described as a symptom complex suggestive of detrusor underactivity, is usually characterized by prolonged urination time with or without a sensation of incomplete bladder emptying, usually with hesitancy, reduced sensation on filling, and slow stream often with storage symptoms. Several causes such as aging, bladder outlet obstruction, diabetes mellitus, neurologic disorders, and nervous injury to the spinal cord, cauda equine, and peripheral pelvic nerve have been assumed to be responsible for the development of UAB. Several contributing factors have been suggested in the pathophysiology of UAB, including myogenic failure, efferent and/or afferent dysfunctions, and central nervous system dysfunction. In this review article, we have described relationships between individual contributing factors and the pathophysiology of UAB based on previous reports. However, many pathophysiological uncertainties still remain, which require more investigations using appropriate animal models.

The Mystery of the Interstitial Cells in the Urinary Bladder

Intrinsic mechanisms to restrain smooth muscle excitability are present in the bladder, and premature contractions during filling indicate a pathological phenotype. Some investigators have proposed that c-Kit⁺ interstitial cells (ICs) are pacemakers and intermediaries in efferent and afferent neural activity, but recent findings suggest these cells have been misidentified and their functions have been misinterpreted. Cells reported to be c-Kit⁺ cells colabel with vimentin antibodies, but vimentin is not a specific marker for c-Kit⁺ cells. A recent report shows that c-Kit⁺ cells in several species coexpress mast cell tryptase, suggesting that they are likely to be mast cells. In fact, most bladder ICs labeled with vimentin antibodies coexpress platelet-derived growth factor receptor α (PDGFRα). Rather than an excitatory phenotype, PDGFRα⁺ cells convey inhibitory regulation in the detrusor, and inhibitory mechanisms are activated by purines and stretch. PDGFRα⁺ cells restrain premature development of contractions during bladder filling, and overactive behavior develops when the inhibitory pathways in these cells are blocked. PDGFRα⁺ cells are also a prominent cell type in the submucosa and lamina propria, but little is known about their function in these locations. Effective pharmacological manipulation of bladder ICs depends on proper identification and further study of the pathways in these cells that affect bladder functions.

Whyever bladder tissue engineering clinical applications still remain unusual even though many intriguing technological advances have been reached?

To prevent problematic outcomes of bowel-based bladder reconstructive surgery, such as prosthetic tumors and systemic metabolic complications, research works, to either regenerate and strengthen failing organ or build organ replacement biosubstitute, have been turned, from 90s of the last century, to both regenerative medicine and tissue engineering.Various types of acellular matrices, naturally-derived materials, synthetic polymers have been used for either "unseeded" (cell free) or autologous "cell seeded" tissue engineering scaffolds. Different categories of cell sources - from autologous differentiated urothelial and smooth muscle cells to natural or laboratory procedure-derived stem cells - have been taken into consideration to reach the construction of suitable "cell seeded" templates. Current clinically validated bladder tissue engineering approaches essentially consist of augmentation cystoplasty in patients suffering from poorly compliant neuropathic bladder. No clinical applications of wholly tissue engineered neobladder have been carried out to radical-reconstructive surgical treatment of bladder malignancies or chronic inflammation-due vesical coarctation. Reliable reasons why bladder tissue engineering clinical applications so far remain unusual, particularly imply the risk of graft ischemia, hence its both fibrous contraction and even worse perforation. Therefore, the achievement of graft vascular network (vasculogenesis) could allow, together with the promotion of host surrounding vessel sprouting (angiogenesis), an effective graft blood supply, so avoiding the ischemia-related serious complications.

γEpithelial Na(+) Channel (γENaC) and the Acid-Sensing Ion Channel 1 (ASIC1) expression in the urothelium of patients with neurogenic detrusor overactivity

OBJECTIVE

To investigate the expression of two types of cation channels, γEpithelial Na(+) Channel (γENaC) and the Acid-Sensing Ion Channel 1 (ASIC1), in the urothelium of controls and in patients affected by neurogenic detrusor overactivity (NDO). In parallel, urodynamic parameters were collected and correlated to the immunohistochemical results.

PATIENTS SUBJECTS AND METHODS

Four controls and 12 patients with a clinical diagnosis of NDO and suprasacral spinal cord lesion underwent urodynamic measurements and cystoscopy. Cold-cup biopsies were frozen and processed for immunohistochemistry and Western Blot. Spearman's correlation coefficient between morphological and urodynamic data was applied. One-way anova followed by Newman-Keuls multiple comparison post hoc test was applied for Western Blot results.

RESULTS

In the controls, γENaC and ASIC1 were expressed in the urothelium with differences in their cell distribution and intensity. In patients with NDO, both markers showed consistent changes either in cell distribution and labelling intensity compared with the controls. A significant correlation between a higher intensity of γENaC expression in the urothelium of patients with NDO and lower values of bladder compliance was detected.

CONCLUSIONS

The present findings show important changes in the expression of γENaC and ASIC1 in NDO human urothelium. Notably, while the changes in γENaC might impair the mechanosensory function of the urothelium, the increase of ASIC1 might represent an attempt to compensate for the excess in local sensitivity.

Pannexin 1 channels play essential roles in urothelial mechanotransduction and intercellular signaling

Urothelial cells respond to bladder distension with ATP release, and ATP signaling within the bladder and from the bladder to the CNS is essential for proper bladder function. In other cell types, pannexin 1 (Panx1) channels provide a pathway for mechanically-induced ATP efflux and for ATP-induced ATP release through interaction with P2X₇ receptors (P2X₇Rs). We report that Panx1 and P2X₇R are functionally expressed in the bladder mucosa and in immortalized human urothelial cells (TRT-HU1), and participate in urothelial ATP release and signaling. ATP release from isolated rat bladders induced by distention was reduced by the Panx1 channel blocker mefloquine (MFQ) and was blunted in mice lacking Panx1 or P2X₇R expression. Hypoosmotic shock induced YoPro dye uptake was inhibited by MFQ and the P2X₇R blocker A438079 in TRT-HU1 cells, and was also blunted in primary urothelial cells derived from mice lacking Panx1 or P2X₇R expression. Rinsing-induced mechanical stimulation of TRT-HU1 cells triggered ATP release, which was reduced by MFQ and potentiated in low divalent cation solution (LDPBS), a condition known to enhance P2X₇R activation. ATP signaling evaluated as intercellular Ca²⁺ wave radius was significantly larger in LDPBS, reduced by MFQ and by apyrase (ATP scavenger). These findings indicate that Panx1 participates in urothelial mechanotransduction and signaling by providing a direct pathway for mechanically-induced ATP release and by functionally interacting with P2X₇Rs.

Effect of detrusor overactivity on the expression of aquaporins and nitric oxide synthase in rat urinary bladder following bladder outlet obstruction

BACKGROUND

Aquaporins (AQPs) have recently been reported to be expressed in rat and human urothelium. Nitric oxide (NO) is thought to play a role in the bladder overactivity related to bladder outlet obstruction (BOO). The purpose of this study is to investigate the effect of BOO on the expression of AQP2-3 and nitric oxide synthase (NOS) isoforms in rat urothelium.

METHODS

Female Sprague-Dawley rats (230-240 g, n = 60) were divided into 2 groups. The control group (n = 30) and the partial bladder outlet obstruction (BOO) group (n = 30). After 4 weeks, we performed a urodynamic study to measure the contraction interval and contraction pressure. The expression and cellular localization of AQP2-3, endothelial nitric oxide synthase (eNOS) and neuronal nitric oxide synthase (nNOS) were determined by Western blot and immunohistochemistry.

RESULTS

On the cystometrogram, the estimated contraction interval time (minutes, mean ± SE) was significantly lower in the BOO group (3.0 ± 0.9) than in the control group (6.3 ± 0.4; p < 0.05). AQP2 was localized in the cytoplasm of the epithelium, whereas AQP3 was found only in the cell membrane of the epithelium. The protein expression of AQP2-3, eNOS and nNOS was significantly increased in the BOO group.

CONCLUSION

Detrusor overactivity induced by BOO causes a significant increase in the expression of AQP2-3, eNOS, and nNOS in rat urinary bladder. This may imply that the AQPs and NOS isoforms have a functional role in the bladder dysfunction that occurs in association with BOO.

The effect of hyperosmolar stimuli and cyclophosphamide on the culture of normal rat urothelial cells in vitro

Highly concentrated urine may induce a harmful effect on the urinary bladder. Therefore, we considered osmolarity of the urine as a basic pathomechanism of mucosal damage. The influence of both cyclophosphamide (CYP) and hyperosmolar stimuli (HS) on the urothelium are not well described. The purpose was to evaluate the effect of CYP and HS on rat urothelial cultured cells (RUCC). 15 Wistar rats were used for RUCC preparation. RUCC were exposed to HS (2080 and 3222 mOsm/l NaCl) for 15 min and CYP (1 mg/ml) for 4 hrs. APC-labelled annexin V was used to quantitatively determine the percentage of apoptotic cells and propidium iodide (PI) as a standard flow cytometric viability probe to distinguish necrotic cells from viable ones. Annexin V-APC (+), annexin V-APC and PI (+), and PI (+) cells were analysed as apoptotic, dead, and necrotic cells, respectively. The results were presented in percentage values. The flow cytometric analysis was done on a FACSCalibur Flow Cytometer using Cell-Quest software. Treatment with 2080 and 3222 mOsm/l HS resulted in 23.7 ± 3.9% and 26.0 ± 1.5% apoptotic cells, respectively, 14.3 ± 1.4% and 19.4 ± 2.7% necrotic cells, respectively and 60.5 ± 1.4% and 48.6 ± 5.3% dead cells, respectively. The effect of CYP on RUCC was similar to the effect of HS. After CYP the apoptotic and necrotic cells were 23.1 ± 0.3% and 17.9 ± 7.4%, respectively. The percentage of dead cells was 57.7 ± 10.8%. CYP and HS induced apoptosis and necrosis in RUCC. 3222 mOsm/l HS had the most harmful effect based on the percentage of necrotic and apoptotic cells.

UV-B induced alteration in purinergic receptors and signaling on HaCaT keratinocytes

Although there are a number of recognized risk factors resulting in cutaneous malignancies, very little is known about the exact mechanism. In keratinocytes different purinergic receptors have been implicated to play essential roles in deciding the fate of the cells through regulating proliferation and differentiation. While P2Y receptors seem to control the former, P2X receptors, among which the P2X(7) receptor is associated with the induction of apoptosis, are likely to be responsible for the latter. Forty mJ/cm(2) UV-B irradiation decreased the number of viable cells as assessed using MTT assay. This irradiation decreased the amount of both P2X(1) and P2Y(2) receptors and essentially destroyed the P2X(7) receptors in surviving cells. Morphology of ATP-induced Ca(2+) transients were altered in irradiated cells compared to control. The amplitude and the rate of rise of the transients were decreased and the return to resting [Ca(2+)](i) prolonged. This observation is consistent with the finding that in control cells mostly ionotropic, while in irradiated cells mostly metabotropic receptors were underlying the response to ATP. These alterations in the expression pattern of purinergic receptors and in the Ca(2+) transients could explain the observed decreased tendency for ATP-induced apoptosis and possibly contribute to the malignant transformation of keratinocytes.

Distribution of interstitial cells of Cajal and expression of nitric oxide synthase after experimental bladder outlet obstruction in a rat model of bladder overactivity

AIMS

Recent studies have showed that interstitial cells (ICs) are widely distributed in the genitourinary tract and have suggested their involvement in spontaneous electrical activity and muscle contraction. Nitric oxide (NO) is thought to play a role in bladder overactivity related with bladder outlet obstruction (BOO). The purposes of this study were to investigate the effect of bladder overactivity induced by BOO on ICs and nitric oxide synthase (NOS) isoforms in rat urinary bladder.

METHODS

Female Sprague-Dawley rats (230-240  g, n = 40) were divided into two groups: control (group Con, n = 20) and partial BOO (group BOO, n = 20). After 4 weeks, urodynamic studies measuring contraction interval and contraction pressure were done. The cellular localization of cKit immunoreactive ICs and the expression of endothelial NOS (eNOS) and neuronal NOS (nNOS) were determined by Western blot and immunohistochemistry in the rat urinary bladder.

RESULTS

Filling cystometry studies demonstrated a reduced interval between voiding contractions and an increased voiding pressure in BOO bladders. The contraction interval time (2.9 ± 0.35  min) was significantly decreased in the BOO group compared to the control (6.1 ± 0.05; P < 0.05). The population of ICs was increased in the suburothelial and muscle layers in BOO bladders. ICs had a close contact with each other and neighboring nNOS expressing cells.

CONCLUSIONS

These results demonstrated an increased population of ICs in the BOO rat model and suggest that the functional change of ICs and NOS isoforms may contribute to the pathophysiology of bladder overactivity induced by BOO.

Basic bladder neurophysiology

Maintenance of normal lower urinary tract function is a complex process that requires coordination between the central nervous system and the autonomic and somatic components of the peripheral nervous system. This article provides an overview of the basic principles that are recognized to regulate normal urine storage and micturition, including bladder biomechanics, relevant neuroanatomy, neural control of lower urinary tract function, and the pharmacologic processes that translate the neural signals into functional results. Finally, the emerging role of the urothelium as a sensory structure is discussed.

Relationship between lower urinary tract symptoms and urinary ATP in patients with benign prostatic hyperplasia or overactive bladder

We investigated whether the improvement of lower urinary tract symptoms (LUTS) and urinary adenosine triphosphate (ATP) level were related. Fifty-seven patients and 13 normal controls were enrolled in this study. All of the male patients had benign prostatic hyperplasia (BPH), and all of the female patients had overactive bladder (OAB). We administered an alpha-1 adrenergic receptor antagonist (tamsulosin hydrochloride) for BPH, while OAB patients received an anti-muscarinic agent (propiverine hydrochloride). Before and after treatment, we examined LUTS and urinary ATP/creatinine ratio. The urinary ATP/creatinine ratio was lower in males than females in both controls and patients. In the BPH patients, administration of the alpha-1 receptor antagonist decreased LUTS and urinary ATP/creatinine ratio, and improvement of LUTS was greater in patients with a high baseline urinary ATP level. In the OAB patients, administration of the anti-muscarinic agent decreased LUTS and urinary ATP/creatinine ratio, and improvement of LUTS was greater in patients with a high baseline urinary ATP level. Improvement of LUTS by treatment with the alpha-1 receptor antagonist or the anti-muscarinic agent was related to the decrease of urinary ATP/creatinine ratio in patients with BPH or OAB. Measurement of urinary ATP can be used as a marker of pathologic bladder function.

Do vesical and voided urine have identical compositions?

OBJECTIVE

In view of the concept that the urothelium is a functioning epithelium, we investigated the hypothesis that the composition of urine is modified as it passes through the urethra from the urinary bladder to the exterior.

MATERIAL AND METHODS

The study was performed in 22 healthy volunteers (13 males, 9 females; mean age 44.6+/-6.2 years). Vesical and voided urine were collected separately; pH was determined using a pH electrode, osmolality by means of micro-osmometry and electrolytes (Na, K) using flame photometry.

RESULTS

Voided urine showed significant increases in pH, osmolality and Na and K concentrations compared to urine contained in the bladder (p < 0.05 for each). Gender and age differences were not significant.

CONCLUSIONS

Vesical urine undergoes changes in some of its components during its passage through the urethra. These findings presumably indicate that the urethral urothelium is a functioning epithelium and also that voided and vesical urine are not identical. The study raises the question to what extent is the analysis of voided urine representative of that of vesical urine?

Cell biology and physiology of the uroepithelium

The uroepithelium sits at the interface between the urinary space and underlying tissues, where it forms a high-resistance barrier to ion, solute, and water flux, as well as pathogens. However, the uroepithelium is not simply a passive barrier; it can modulate the composition of the urine, and it functions as an integral part of a sensory web in which it receives, amplifies, and transmits information about its external milieu to the underlying nervous and muscular systems. This review examines our understanding of uroepithelial regeneration and how specializations of the outermost umbrella cell layer, including tight junctions, surface uroplakins, and dynamic apical membrane exocytosis/endocytosis, contribute to barrier function and how they are co-opted by uropathogenic bacteria to infect the uroepithelium. Furthermore, we discuss the presence and possible functions of aquaporins, urea transporters, and multiple ion channels in the uroepithelium. Finally, we describe potential mechanisms by which the uroepithelium can transmit information about the urinary space to the other tissues in the bladder proper.

Distinct apical and basolateral membrane requirements for stretch-induced membrane traffic at the apical surface of bladder umbrella cells

Epithelial cells respond to mechanical stimuli by increasing exocytosis, endocytosis, and ion transport, but how these processes are initiated and coordinated and the mechanotransduction pathways involved are not well understood. We observed that in response to a dynamic mechanical environment, increased apical membrane tension, but not pressure, stimulated apical membrane exocytosis and ion transport in bladder umbrella cells. The exocytic response was independent of temperature but required the cytoskeleton and the activity of a nonselective cation channel and the epithelial sodium channel. The subsequent increase in basolateral membrane tension had the opposite effect and triggered the compensatory endocytosis of added apical membrane, which was modulated by opening of basolateral K(+) channels. Our results indicate that during the dynamic processes of bladder filling and voiding apical membrane dynamics depend on sequential and coordinated mechanotransduction events at both membrane domains of the umbrella cell.

Roles of mechanosensitive ion channels in bladder sensory transduction and overactive bladder

In the storage phase, mechanical stretch stimulates bladder afferents. These signals generate sensations and trigger voiding responses, however the precise mechanisms by which mechanical stimuli excite bladder afferents are yet to be explored. For mechanosensory transduction, the presence of mechanosensors is essential in the peripheral sensory systems including sensory nerve endings, urothelium and others. There is increasing evidence that mechanosensitive ion channels, such as degenerin/epithelial Na(+) channel (ENaC) and transient receptor potential (TRP) channel families, play key roles in the mechanosensory transduction of the urinary bladder. Pharmacological interventions targeting mechanosensitive ion channels may provide a new strategy for the treatment of bladder dysfunction.

Sensitization of pelvic afferent nerves in the in vitro rat urinary bladder-pelvic nerve preparation by purinergic agonists and cyclophosphamide pretreatment

Effects of purinergic agonists (alpha,beta-meATP and ATP) and cyclophosphamide-induced cystitis on bladder afferent nerve (BAN) activity were studied in an in vitro bladder-pelvic nerve preparation. Distension of the bladder induced spontaneous bladder contractions that were accompanied by multiunit afferent firing. Intravesical administration of 40 and 130 microM alpha,beta-meATP increased afferent firing from 27 +/- 3 to 53 +/- 6 and 61 +/- 2 spikes/s, respectively, but did not change the maximum amplitude of spontaneous bladder contractions. Electrical stimulation on the surface of the bladder elicited action potentials (AP) in BAN. alpha,beta-meATP decreased the voltage threshold from 9.0 +/- 1.2 to 3.5 +/- 0.5 V (0.15-ms pulse duration) and increased the area of the APs (82% at 80-V stimulus intensity). These effects were blocked by TNP-ATP (30 microM). ATP (2 mM) applied in the bath produced similar changes in BAN activity. These effects were blocked by bath application of PPADS (30 microM). Neither TNP-ATP nor PPADS affected BAN activity induced by distension of the bladder. Cystitis induced by pretreatment of the rats with cyclophosphamide (100 mg/kg ip) increased afferent firing in response to isotonic bladder distension (10-40 cmH(2)O), decreased the threshold, and increased the area of evoked APs. The increase in afferent firing at 10 cmH(2)O intravesical pressure was reduced 52% by PPADS. These results indicate that purinergic agonists acting on P2X receptors and cystitis induced by cyclophosphamide can increase excitability of the BANs.

Effects of propiverine and naftopidil on the urinary ATP level and bladder activity after bladder stimulation in rats

We examined the effects of propiverine hydrochloride and naftopidil on the urinary ATP level and bladder activity after bladder stimulation in rats. Thirty-nine female rats were divided into a control group, a propiverine group, and a naftopidil group. Rats in the propiverine and naftopidil groups were administered 1 ml/day of propiverine or naftopidil dissolved in water at 5mg/ml, while animals in the control group were administered 1 ml of water only. After 2 weeks, 18 rats (6 per group) underwent continuous cystometry with physiological saline or 0.1% acetic acid solution and their bladder activity was recorded. In the remaining 21 rats (7 per group), 0.1% acetic acid solution was infused into the bladder and the urinary ATP level was measured before and after stimulation (days 0-7). During cystometry with acetic acid in the control group, the interval between bladder contractions was shorter and the maximum bladder contraction pressure was higher than the results for cystometry with physiological saline. The maximum bladder contraction pressure was also increased in the naftopidil group, but such a change was not seen in the propiverine group. The urinary ATP level increased significantly in all three groups after the infusion of acetic acid, but the increase of ATP was smaller in the propiverine group (45% of control) and the naftopidil group (62% of control) than in the control group on day 0. Therefore, the inhibitory effect of propiverine and naftopidil on bladder activity may be partly due to blocking ATP release from the bladder epithelium.

A survey of commonalities relevant to function and dysfunction in pelvic and sexual organs

Micturition, defecation and sexual function are all programmed through spinal reflexes that are under descending control from higher centres. Interaction between these reflexes can clearly be perceived, and evidence is accumulating the dysfunction in one reflex is often associated with dysfunction in another. In this article, we describe some of the basic properties and neural control of the smooth muscles mediating the reflexes, reviewing the common features that underlie these reflex functions, and what changes may be responsible for dysfunction. We propose that autonomic control within the pelvis predisposes pelvic and sexual organs to crosstalk, with the consequence that diseases and conditions of the pelvis are subject to convergence on a functional level. It should be expected that disturbance of the function of one system will inevitably impact adjacent systems.

Alterations to network of NO/cGMP-responsive interstitial cells induced by outlet obstruction in guinea-pig bladder

Interstitial cells (ICs) play a role in regulating normal bladder activity. This study explores the possibility that the sub-urothelial and muscle networks of NO/cGMP-responsive ICs are altered in animals with surgically induced outflow obstruction. In sham-operated animals, the urothelium comprised NO-stimulated cGMP-positive (cGMP(+)) umbrella cells, an intermediate layer and a basal layer that stained for nNOS. cGMP(+) sub-urothelial interstitial cells (su-ICs) were found below the urothelium. cGMP(+) cells were also associated with the outer muscle layers: on the serosal surface, on the surface of the muscle bundles and within the muscle bundles. Several differences were noted in tissues from obstructed animals: (1) the number of cGMP(+) umbrella cells and intensity of staining was reduced; (2) the intermediate layer of the urothelium consisted of multiple cell layers; (3) the su-IC layer was increased, with cells dispersed being throughout the lamina propria; (4) cGMP(+) cells were found within the inner muscle layer forming nodes between the muscle bundles; (5) the number of cells forming the muscle coat (serosa) was increased; (6) an extensive network of cGMP(+) cells penetrated the muscle bundles; (7) cGMP(+) cells surrounded the muscle bundles and nodes of ICs were apparent, these nodes being associated with nerve fibres; (8) nerves were found in the lamina propria but rarely associated with the urothelium. Thus, changes occur in the networks of ICs following bladder outflow obstruction. These changes must have functional consequences, some of which are discussed.

Enhanced adenosine triphosphate release from the urothelium of patients with painful bladder syndrome: a possible pathophysiological explanation

PURPOSE

We established the level of adenosine triphosphate release by the urothelium in patients with painful bladder syndrome and compared it with that from the normal human bladder.

MATERIALS AND METHODS

Biopsies of urothelium from patients with painful bladder syndrome were subjected to stretch by 130% and 150% of the original length, and 10 Hz electric stimulation. A luciferase assay was used to quantify adenosine triphosphate release. The neurotoxin tetrodotoxin was used to block the neuronal source of adenosine triphosphate release.

RESULTS

There was a significantly greater release of adenosine triphosphate following mechanical stretch of the urothelium from painful vs control bladders. The increase in adenosine triphosphate release in painful vs control bladders was statistically significant whether expressed in absolute values (mean +/- SE 3,791.4 +/- 667.9 vs 77.6 +/- 16.2 pM gm(-1) tissue) or as an increase over baseline (282.2% +/- 24.8% vs 175.4% +/- 21.7%). Similarly there was a significant release of adenosine triphosphate following electrical field stimulation of the urothelium from painful vs control bladders (1,348.6 +/- 278.2 vs 61.7 +/- 10.1 pM gm(-1) tissue, p <0.005), representing a 278% +/- 41.5% vs 137.9% +/- 4.4% increase above baseline (p <0.005). The source of adenosine triphosphate release was nonneuronal in 89% of painful bladders and in 84% of control bladders.

CONCLUSIONS

There is a significantly increased level of adenosine triphosphate release from the urothelium of painful bladders in comparison to that from normal bladders, suggesting an important potential functional role for adenosine triphosphate in this condition.

The uroepithelial-associated sensory web

An important, but not well understood, function of epithelial cells is their ability to sense changes in their extracellular environment and then communicate these changes to the underlying nervous, connective, and muscular tissues. This communication is likely to be important for tube- and sac-shaped organs such as blood vessels, the lungs, the gut, and the bladder, whose normal function can be modulated by stimuli initiated within the epithelium. We propose that the uroepithelium, which lines the renal pelvis, ureters, and inner surface of the bladder, functions as an integral part of a 'sensory web.' Through uroepithelial-associated channels and receptors, the uroepithelium receives sensory 'inputs' such as changes in hydrostatic pressure and binding of mediators including adenosine triphosphate (ATP). These input signals stimulate membrane turnover in the outermost umbrella cell layer and release of sensory 'outputs' from the uroepithelium in the form of neurotransmitters and other mediators that communicate changes in the uroepithelial milieu to the underlying tissues, altering their function. The global consequence of this sensory web is the coordinated function of the bladder during the cycles of filling and voiding, and disruption of this web is likely to lead to bladder dysfunction.

Amiloride-sensitive ion channels in urinary bladder epithelium involved in mechanosensory transduction by modulating stretch-evoked adenosine triphosphate release

OBJECTIVES

To examine the possibility that mechanosensitive ion channels, including epithelial Na+ channels (ENaC), are implicated in mechanosensory transduction of the rat urinary bladder.

METHODS

Cystometry with continuous infusion was performed to investigate the effect of intravesically perfused amiloride (a blocker of ENaC) on micturition reflex in urethane-anesthetized female rats. Bladder strips with or without epithelium suspended in organ bath were subjected to varying degrees of mechanical stretch (up to 50%). A luciferin-luciferase assay was used to quantify the change of stretch-evoked adenosine triphosphate (ATP) release by amiloride. The ENaC gene expression was assessed by reverse transcriptase-polymerase chain reaction. The expression and localization of ENaC proteins was examined using immunofluorescent staining.

RESULTS

The intravesical perfusion of 1 mM amiloride significantly reduced the frequency of reflex voiding during bladder filling. This effect of amiloride was reversible by washing out the drug. The peak amplitude of micturition pressure was not affected by amiloride. The stretch-evoked ATP release, most of which (more than 90%) came from epithelial layer, was greatly diminished by 1 mM amiloride (from 443 to a 22% increase from basal level at 50% stretch of the original length). The alpha, beta, and gamma-ENaC subunit proteins and genes were expressed in the rat bladder epithelium.

CONCLUSIONS

The amiloride-sensitive mechanosensitive channel, including ENaC, expressed in the rat bladder epithelium might be involved in the mechanosensory transduction mechanism by controlling stretch-evoked ATP release.

The detrusor muscle: an innocent victim of bladder outlet obstruction

OBJECTIVES

Benign prostatic hyperplasia (BPH) is considered a frequent cause of bladder outlet obstruction (BOO) and lower urinary tract symptoms (LUTS), although the physiopathologic mechanism through which BPH causes LUTS is not clear. Several morphologic and functional modifications of the bladder detrusor have been described in patients with BPH and could play a direct role in determining symptoms. The opinion is spreading that the enlarged prostates in patients with LUTS is nothing more than a mere bystander. Evidence has accumulated, however, supporting the role of BPH-related BOO as the direct cause determining bladder dysfunction and indirectly causing urinary symptoms. The present review addresses the bladder response to BOO, particularly focusing on the physiopathologic cascade that links obstructive BPH to bladder dysfunction.

METHODS

A literature review of peer-reviewed articles has been performed, including both in vivo and in vitro studies on human tissue and animal model experiments.

RESULTS

Epithelial and smooth muscle cells in the bladder wall are mechanosensitive, and in response to mechanical stretch stress caused by BOO, undergo modifications of gene expression and protein synthesis. This process involves several transduction mechanisms and finally alter the ultrastructure and physiology of cell membranes, cytoskeleton, contractile proteins, mitochondria, extracellular matrix, and neuronal networks.

CONCLUSIONS

BOO is the initiator of a physiopathologic cascade leading to deep changing of bladder structure and function. Before being a direct cause of storing-phase urinary symptoms, the bladder is the first innocent victim of prostatic obstruction.

Arousing Properties of the Vulvar Epithelium

PURPOSE

The initiation of genital tactile stimulation is regarded as a precursor to sexual arousal and perhaps in women it is the most easily recognized initiator of central nervous system arousal. Unfortunately little published material details the specific mechanisms preceding arousal, beginning at the epithelial level, which are the sensory precursors to arousal. Little is known about its cutaneous receptors, nerves and the other histochemical properties of this epithelial tissue that contribute to sexual arousal. Sexual sensitivity evaluations target female genital somatosensory pathways for cutaneous sensation by testing evoked potentials of nerves, hot/cold and vibratory sensory discrimination. The anatomical bases of these several sensibilities form a subject for future investigation. We reviewed the known influences and mechanisms responsible for the arousing properties of the epithelium in the female external genitalia as well neural pathways associated with sexual arousal originating from the vulvar epithelium.

MATERIALS AND METHODS

A comprehensive review was done of published, relevant clinical and histological material in human and nonhuman vertebrate studies.

RESULTS

Tactile stimulation of the vulvar epithelium initiates changes suggesting complex integrative mechanisms. Influences of skin temperature, hormonal environment, mechanical tissue compliance and inflammation as well as the large number of transmitters and neuropeptides involved in peripheral pathways serving female sexual arousal speak of a direct sensory role.

CONCLUSIONS

Genital epithelial cells may actively participate in sensory function to initiate sexual arousal by expressing receptors and releasing neurotransmitters in response to stimuli, resulting in epithelial-neuronal interactions.

Does the composition of voided urine reflect that of the renal pelvis?

Studies have shown that the urothelium has a transport function and that urine composition changes on its way through the urinary tract. In this study, we investigated the hypothesis that the composition of voided urine differs from and does not reflect that of the renal pelvis. Urine samples were obtained from the renal pelvis and voided urine of 18 healthy volunteers (mean age 36.2+/-5.1 SD years, 10 men, 8 women). The pH was determined using a pH electrode, osmolality by means of micro-osmometry and Na and K using flame photometry. In comparison to the urine of the renal pelvis, voided urine showed significant increases in pH, osmolality and Na and K concentrations (P<0.05 for each). There were no significant differences in gender and age. This study has demonstrated that the pH, osmolality, Na and K of voided urine differ significantly from the values in the renal pelvis. Urine composition is thus modified as it passes through the urinary tract, which would support the concept of a dynamic urothelium. The composition of voided urine does not seem to compare to renal pelvic urine. This concept needs to be considered in urine analysis evaluation and its relation to renal function.

Endogenous nitric oxide/cGMP signalling in the guinea pig bladder: evidence for distinct populations of sub-urothelial interstitial cells

We have examined structures that may operate by using nitric oxide (NO)/soluble guanylyl cyclase (sGC) signalling in the lamina propria of the guinea pig bladder. Cells on the luminal surface of the urothelium and sub-urothelial interstitial cells (SU-ICs) responded to NO with a rise in cGMP. The distribution of these different cells varied between the base, lateral wall and dome. In the base, two regions were identified: areas with sparse surface urothelial cells and areas with a complete covering. A layer of cGMP-positive (cGMP(+)) cells (up to 10 cells deep) was found in the base. cGMP(+)/SU-ICs were also observed in the lateral wall. However, here, the cGMP(+) cells were confined to a layer of only 1-2 cells immediately below the basal urothelial layer (basal cGMP(+)/SU-ICs). Below these cGMP(+)/SU-ICs lay cells that had a similar structure but that showed little cGMP accumulation (deep cGMP(-)/SU-ICs). Both basal and deep SU-ICs expressed the beta1 subunit of sGC and the cGMP-dependent protein kinase I (cGKI), suggesting that the deep SU-ICs can sense NO and signal via cGMP. By using BAY 41-2272, a sensor of endogenous NO production, NO-dependent cGMP synthesis was observed primarily in the basal SU-ICs. A third population of cGKI(+)/cGMP(-) cells was seen to lie immediately below the basal urothelial layer. These cells ("necklace" cells) were less numerous than SU-ICs and extended linking processes suggesting a network. The specific functions of these structures are not known but they may contribute to the emerging multiple roles of the urothelium associated with the generation of bladder sensation.

Assessment of urodynamic bladder behavior on filling with solutions representing physiological extremes of urinary osmolarity

OBJECTIVE

Verify if there is any difference in sensitive and motor bladder response in the presence of solutions with different osmolarities, simulating physiological extremes of urinary osmolarity.

MATERIALS AND METHODS

Thirty-three patients (24 men and 9 women) with mean age of 46.4 years (8 to 87 years) took part in this study. They were all subjected to 2 consecutive urodynamic examinations. In each exam, the vesical filling was accomplished by using a hyperosmolar (1000 mOsm/L) or hypo-osmolar (100 mOsm/L) sodium chloride solution in similar speed. The sequence in which each solution was instilled was determined by a double blind draw. The urodynamic results obtained from the infusion of both solutions were compared, regardless the sequence of administration.

RESULTS

Fifteen patients (45.4%) showed detrusor hyperactivity, 12 of whom with neurological antecedents. The mean age of those with detrusor hyperactivity was 45.8 years, against 46.9 for those without hyperactivity. The infusion of the hyperosmolar/hypo-osmolar solution generated the following results, when comparing patients without vs. with detrusor hyperactivity: initial sensation of vesical filling (mL): 167.5/159.2 vs. 134.9/157.3 (p > 0.05); volume of occurrence of the first involuntary bladder contraction (mL): 163.9/151.9 (p > 0.05); detrusor micturition pressure (cm H2O): 24.0/24.4 vs. 13.8/27.5 (p > 0.05).

CONCLUSION

The vesical filling with solutions simulating extreme urinary osmolarities, accomplished with similar speed and without previous identification, did not likewise alter the sensitive and motor urodynamic behavior in the current study.

In vivo effects of botulinum toxin A on visceral sensory function in chronic spinal cord-injured rats

OBJECTIVES

To analyze the in vivo effects of botulinum toxin type A (BTX-A) on visceral sensory function in chronic spinal cord-injured (SCI) rats.

METHODS

One group of rats underwent spinal cord transection at the T8-T9 level (SCI) and the other group was left untreated. In 21 days, baseline open cystometrography (CMG) was performed. The rats were then treated intravesically with either 1 mL of 1% protamine sulfate (PS) to increase urothelial permeability or saline, followed by either 1 mL of BTX-A (20 U) or saline. CMG was repeated 48 hours after instillation, and any changes in the bladder contraction frequency and amplitude were evaluated.

RESULTS

After the instillation of PS and BTX-A or BTX-A alone, the bladder contraction frequency was significantly decreased in the SCI rats compared with the control rats (P < 0.05); no change was seen in the contraction amplitude. When normal rats were given intravesical PS and/or BTX-A, or SCI animals were treated with PS alone, neither the frequency nor the amplitude of the contractions was affected. Also, no significant differences were found in the bladder contraction frequency or amplitude of contractions in any animal treated with instillation of saline alone.

CONCLUSIONS

Intravesical BTX-A inhibits bladder sensory mechanisms by reducing the frequency of bladder contractions in an SCI rat model. Furthermore, our results suggest that intravesically applied BTX-A does not penetrate to the smooth muscle layer even after PS disruption of the bladder urothelium. These findings may have important clinical applications in treating overactive bladders after SCI.

Enhanced ATP release from rat bladder urothelium during chronic bladder inflammation: Effect of botulinum toxin A

The effects of mechanoreceptor stimulation and subsequent ATP release in cyclophosphamide evoked chronic bladder inflammation was examined to demonstrate: (1) whether inflammation modulates ATP release from bladder urothelium and (2) whether intravesical botulinum toxin A administration inhibits urothelial ATP release, a measure of sensory nerve activation. ATP release was measured from rat bladders in a Ussing chamber, an apparatus that allows one to separately measure resting and mechanoreceptor evoked (e.g. hypoosmotic stimulation) ATP release from urothelial and serosal sides of the bladder. Cystometry was utilized to correlate changes in ATP release with alterations in the frequency of voiding and non-voiding bladder contractions, in vivo measures of bladder afferent activity. The resting urothelial release of ATP was not significantly affected by either cyclophosphamide or botulinum toxin A treatment. However, evoked ATP release following hypoosmotic stimulation was significantly increased (i.e. 94%) in chronic cyclophosphamide treated bladder urothelium compared to control bladders. In addition, botulinum toxin A treatment significantly reduced hypoosmotic shock induced ATP release in cyclophosphamide treated animals by 69%. Cystometry revealed that cyclophosphamide and botulinum toxin A treatments altered non-voiding (i.e. cyclophosphamide increased, botulinum toxin A decreased) but not voiding contraction frequency suggesting that alterations in urothelial ATP release selectively diminished underlying bladder C-fiber nerve activity. Finally, intravesical instillation of botulinum toxin A did not affect ATP release from the serosal side implying that its effects were confined to the urothelial side of the bladder preparation.

A biomimetic tissue from cultured normal human urothelial cells: analysis of physiological function

The urinary bladder and associated tract is lined by the urothelium. Once considered as just an impermeable epithelium, it is becoming evident that the urothelium not only functions as a volume-accommodating urinary barrier but has additional roles, including sensory signaling. Lack of access to normal human urothelium has hampered physiological investigation, and although cell culture systems have been developed, there has been a failure to demonstrate that normal human urothelial (NHU) cells grown in vitro retain the capacity to form a functional differentiated urothelium. The aim of this study was to develop a biomimetic human urothelium from NHU cell cultures. Urothelial cells isolated from normal human urothelium and serially propagated as monolayers in serum-free culture were homogeneous and adopted a proliferative, nondifferentiated phenotype. In the presence of serum and physiological concentrations of calcium, these cells could be reproducibly induced to form stratified urothelia consisting of basal, intermediate, and superficial cells, with differential expression of cytokeratins and superficial tight junctions. Functionally, the neotissues showed characteristics of native urothelium, including high transepithelial electrical resistance of >3,000 Ω·cm2, apical membrane-restricted amiloride-sensitive sodium ion channels, basal expression of Na+-K+-ATPase, and low diffusive permeability to urea, water, and dextran. This model represents major progress in developing a biomimetic human urothelial culture model to explore molecular and functional relationships in normal and dysfunctional bladder physiology.

Expression of neuronal nitric oxide synthase (nNOS) and nitric-oxide-induced changes in cGMP in the urothelial layer of the guinea pig bladder

The urothelium plays a sensory role responding to deformation of the bladder wall; this involves the release of adenosine trisphosphate (ATP) and nitric oxide (NO), which affect afferent nerve discharge and bladder sensation. The urothelial cells responsible for producing ATP and NO and the cellular targets, other than afferent nerves, for ATP and NO remain largely unexplored. Sub-urothelial interstitial cells (SU-ICs) lie immediately below the urothelium and respond to NO with a rise in cGMP. To determine which cells might target SU-ICs by producing NO, areas of dome, lateral wall and base wall were treated with isobutyl-methyl-xanthine, exposed to the NO donor diethylamino NONOate and then fixed for immunohistochemistry. Surface urothelial cells (SUCs) in the base and dome expressed neuronal nitric oxide synthase (nNOS), whereas those in the lateral wall did not. Distinct populations of SUCs were present in the bladder base. SUCs with significant amounts of nNOS lay adjacent to cells with low levels of nNOS. In specific base regions, the few SUCs present contained nNOS within discrete intracellular particles. In the basal urothelial cell (BUC) layer of the lateral wall, nNOS-positive (NOS(+)) BUCs neither showed an elevation in cGMP in response to NO, nor expressed the beta1 sub-unit of soluble guanylate cyclase, protein kinase I or protein kinase II. Thus, they produced but did not respond to NO. The BUC layer also stained for the stem cell factor c-Kit suggesting its involvement in urothelial cell development. No NOS(+) BUCs were present in the SUC-sparse region in the bladder base. Exogenous NO produced an elevation in cGMP in SUCs and SU-ICs. The distribution and proportion of these target cells varied between the dome, lateral wall and base. cGMP(+) SU-ICs were present as a dense layer in the bladder base but were rarely seen in the lateral wall, which contained nNOS(+) BUCs. No nNOS(+) BUCs and cGMP(+) SU-ICs were apparent in the dome. The degree of complexity in nNOS distribution and NO target cells is therefore greater than has previously been described and may reflect distinct physiological functions that have yet to be identified.

Immunohistochemical evidence of vanilloid receptor 1 in normal human urinary bladder

PURPOSE

Experimental and clinical evidences have shown the importance of the vanilloid receptor 1 (TRPV1) in the lower urinary tract. In humans, this receptor has been detected in nerve endings of primary sensory neurons, smooth muscle and connective tissue cells and in the rat also in the urothelium. The aim of this study is to identify, by immunohistochemistry, the cell types expressing TRPV1 in the human urinary bladder.

MATERIAL AND METHODS

Specimens, obtained from normal urinary bladder by multiple biopsy and from ureter at the time of radical nefrectomy for renal cell carcinoma, were fixed and frozen. Full-thickness sections were processed for light and fluorescence microscopes. To label the TRPV1, three polyclonal antibodies were used: the anti-capsaicin receptor, the anti-VR1 (N-15) and the anti-VR1 (C-15).

RESULTS

Urothelium, smooth muscle cells, mast cells and endothelium were labelled and the labelling was intracytoplasmatic. In the urothelial cells, the labelling was slightly granular. In the bladder urothelium, the superficial cells were more intensely stained than the basal and club-shaped cells. VR1-positive nerve fibers were seen running single and/or in groups in the sub-urothelium and as single varicose fibers in the muscle coat, and VR1-positive nerve endings in the urothelium.

CONCLUSION

The present findings provide the evidence of the presence of TRPV1 on normal human urothelium where it could have important implications in the mechanism of action of intravesical vanilloids (capsaicin and resiniferatoxin).

Expression and function of bradykinin B1 and B2 receptors in normal and inflamed rat urinary bladder urothelium

The bladder urothelium exhibits dynamic sensory properties that adapt to changes in the local environment. These studies investigated the localization and function of bradykinin receptor subtypes B1 and B2 in the normal and inflamed (cyclophosphamide (CYP)-induced cystitis) bladder urothelium and their contribution to lower urinary tract function in the rat. Our findings indicate that the bradykinin 2 receptor (B2R) but not the bradykinin 1 receptor (B1R) is expressed in control bladder urothelium. B2R immunoreactivity was localized throughout the bladder, including the urothelium and detrusor smooth muscle. Bradykinin-evoked activation of this receptor elevated intracellular calcium (EC(50) = 8.4 nM) in a concentration-related manner and evoked ATP release from control cultured rat urothelial cells. In contrast, B1R mRNA was not detected in control rat urinary bladder; however, following acute (24 h) and chronic (8 day) CYP-induced cystitis in the rat, B1R mRNA was detected throughout the bladder. Functional B1Rs were demonstrated by evoking ATP release and increases in [Ca(2+)](i) in CYP (24 h)-treated cultured rat urothelial cells with a selective B1 receptor agonist (des-Arg(9)-bradykinin). Cystometry performed on control anaesthetized rats revealed that intravesical instillation of bradykinin activated the micturition pathway. Attenuation of this response by the P2 receptor antagonist PPADS suggests that bradykinin-induced micturition facilitation may be due in part to increased purinergic responsiveness. CYP (24 h)-treated rats demonstrated bladder hyperactivity that was significantly reduced by intravesical administration of either B1 (des-Arg(10)-Hoe-140) or B2 (Hoe-140) receptor antagonists. These studies demonstrate that urothelial expression of bradykinin receptors is plastic and is altered by pathology.

The uroepithelium: not just a passive barrier

The uroepithelium lines the inner surface of the renal pelvis, the ureters, and the urinary bladder, where it forms a tight barrier that allows for retention of urine, while preventing the unregulated movement of ions, solutes, and toxic metabolites across the epithelial barrier. In the case of the bladder, the permeability barrier must be maintained even as the organ undergoes cyclical changes in pressure as it fills and empties. Beyond furthering our understanding of barrier function, new analysis of the uroepithelium is providing information about how detergent-insoluble membrane/protein domains called plaques are formed at the apical plasma membrane of the surface umbrella cells, how mechanical stimuli such as pressure alter exocytic and endocytic traffic in epithelial cells such as umbrella cells, and how changes in pressure are communicated to the underlying nervous system.

Overexpression of epithelial sodium channels in epithelium of human urinary bladder with outlet obstruction

OBJECTIVES

To examine whether the epithelial sodium channel (ENaC) is expressed in the human urinary bladder and how its expression changes in association with outlet obstruction. Detrusor instability occurs in association with bladder outlet obstruction. The increase of afferent activity is one of the possible mechanisms for this detrusor instability. The ENaC expressed in mammals has been implicated in various mechanosensory functions.

METHODS

Specimens of urinary bladder mucosa were obtained from 9 controls and 9 patients with bladder outlet obstruction verified by the International Prostate Symptom Score, prostate volume, and urodynamic tests. In 7 patients with outlet obstruction, involuntary detrusor contraction was demonstrated. The expression and localization of ENaC proteins was examined using immunofluorescent staining. The quantification of ENaC gene expression was assessed by real-time reverse transcriptase-polymerase chain reaction.

RESULTS

The alpha-ENaC, beta-ENaC, and gamma-ENaC proteins were expressed in human urinary bladder epithelium with outlet obstruction, and the alpha-ENaC and gamma-ENaC proteins were virtually unstained in the control bladders. Alpha-ENaC, beta-ENaC, and gamma-ENaC mRNA were detected in 1, 6, and 4 of 9 control bladders, respectively. Each ENaC mRNA was clearly present in all obstructed bladders. The expression levels of each subunit in the obstructed bladders were significantly greater than those in controls. The quantified ENaC expression correlated significantly with the storage symptom score.

CONCLUSIONS

The ENaC expressed in the bladder epithelium might be implicated in the mechanosensory transduction in the bladder afferent pathways, thereby inducing detrusor instability by outlet obstruction.

Botulinum toxin A inhibits ATP release from bladder urothelium after chronic spinal cord injury

The effects of mechanoreceptor stimulation and subsequent ATP release in spinal cord injured and normal bladders was examined to demonstrate if spinal cord injury (SCI) modulates the basal or evoked release of ATP from bladder urothelium and whether intravesical botulinum toxin A (BTX-A) administration inhibits urothelial ATP release, a measure of sensory nerve activation. A Ussing chamber was used to isolate and separately measure resting and mechanoreceptor evoked (e.g. hypoosmotic stimulation) ATP release from urothelial and serosal sides of the bladder. Following spinal cord injury, resting urothelial release of ATP was ninefold higher than that of normal rats. Botulinum toxin A instillation did not significantly affect the resting release of ATP after spinal cord injury. Evoked ATP release following hypoosmotic stimulation was significantly higher in chronic spinal cord injured compared to normal rat bladders. However, botulinum toxin A treatment markedly reduced ATP release in spinal cord injured bladders by 53% suggesting that ATP release by mechanoreceptor stimulation, as opposed to basal release, occurs by exocytotic mechanisms. In contrast, there was no significant difference in basal or evoked ATP release from bladder serosa following spinal cord injury. Moreover, intravesical instillation of botulinum toxin A did not affect ATP release from the serosal side after spinal cord injury, suggesting that its effects were confined to the urothelial side of the bladder preparation. In summary: (1) increased release of ATP from the urothelium of spinal cord injured bladders may contribute to the development of bladder hyperactivity and, (2) mechanoreceptor stimulated vesicular ATP release, as opposed to basal non-vesicular release of ATP, is significantly inhibited in spinal cord injured bladders by intravesical instillation of botulinum toxin A. These results may have important relevance in our understanding of the mechanisms underlying plasticity of bladder afferent pathways following SCI.

P2Y-mediated Ca2+ response is spatiotemporally graded and synchronized in sensory neurons: a two-photon photolysis study

ATP is thought to be an initiator and modulator of noxious pain sensation. We employed two-photon photolysis to apply ATP locally and transiently, thus mimicking ATP release upon cell damage or exocytosis. Using this technique, an increase in intracellular Ca2+ concentration ([Ca2+]i) was induced via P2Y receptors in individual sensory neurons, or in a neurite region. The ATP-induced [Ca2+]i rise was attenuated by applications of either a phospholipase C inhibitor, or inhibitors for IP3 or ryanodine receptors. These results indicate that intracellular Ca2+ stores play a major role in contributing to the increase in [Ca2+]i. Spatiotemporal analysis revealed that local and transient applications of ATP increased [Ca2+]i by release from intracellular stores, but in a unique, graded, and synchronized manner. 1) As the duration of local ATP application was prolonged, the latency decreased and the magnitude of the [Ca2+]i rise increased; 2) The time course of the rising phase of the [Ca2+]i response to ATP was essentially the same over the cell body, once [Ca2+]i had started to rise. It is anticipated that sensory responses may be modulated variably, depending on the spatiotemporal characteristics of the ATP-related [Ca2+]i profile.

P2X2 and P2X3 receptor expression in human bladder urothelium and changes in interstitial cystitis

OBJECTIVE

To investigate whether the expression of P2X(3) receptors (implicated in the pathophysiology of pain) is altered in human bladder urothelium from patients with interstitial cystitis (IC, a major symptom of which is pain), and as P2X(2) receptors can be co-expressed with P2X(3) receptors, to assess their expression also.

PATIENTS AND METHODS

Bladder tissue samples were collected from patients undergoing cystectomy or radical prostatectomy. Patients with IC were diagnosed using the international criteria. RNA protein expression levels of both receptors were evaluated using reverse transcription-polymerase chain reaction (PCR), real-time quantitative PCR and Western blot analysis.

RESULTS

P2X(2) was expressed in the human urothelium, in a glycosylated form. There was less gene expression of P2X(3) in IC urothelium, whereas P2X(2) gene expression was unchanged. This contrasted with the protein expression, which was increased for both P2X(2) and P2X(3).

CONCLUSION

This is the first report of the expression of the P2X(2) receptor in human bladder urothelium. There was greater protein expression of both P2X(2) and P2X(3) in IC bladder urothelium which did not directly correlate with the gene expression. Changes in expression of P2X(2) and P2X(3) receptors may contribute to the pain that patients with IC have, and might provide novel drug targets.

Electrical characteristics of suburothelial cells isolated from the human bladder

PURPOSE

We measured the membrane electrical characteristics as well as the response to adenosine triphosphate of cells isolated from the suburothelial layer of the bladder.

MATERIALS AND METHODS

Suburothelial cells were isolated from biopsy samples of human bladder by collagenase disruption. Electrophysiological measurements were done under current and voltage clamp to record membrane potential and ionic currents using patch pipettes with a K+ based filling solution. Intracellular [Ca2+] was measured with Fura-2.

RESULTS

Cells were different from epithelial cells by their spindle-shaped appearance with projections at either end. The cells stained for vimentin but epithelial and smooth muscle cells did not. The cells had small membrane capacitance (27 +/- 16 pF) and a specific membrane resistance of 90 +/- 48 x 10(9) Omega cm2. Average membrane potential was -63 +/- 14 mV but cells showed spontaneous spikes or random fluctuations of membrane potential. A small net inward current was superimposed by a larger outward current. Inward current was attenuated by the removal of extracellular Ca. Outward current showed large spontaneous fluctuations and was greatly decreased by 30 mM tetraethyl ammonium chloride. Adenosine triphosphate (30 to 100 microM) elicited an inward current of about 50 pA and large intracellular Ca2+ transients.

CONCLUSIONS

These cells are electrically active which, in conjunction with the previous observation of connexin 43 labeling, suggests that they could act as an electrical network. A quantitative model of voltage distribution in such a network after the generation of inward current suggests that individual cells could not act as pacemakers, but rather a group of simultaneously activated cells could exert a peripheral excitatory effect that would amplify the magnitude of the original response. The implications of this in terms of bladder sensation are discussed.

Hydrostatic pressure-regulated ion transport in bladder uroepithelium

The effect of hydrostatic pressure on ion transport in the bladder uroepithelium was investigated. Isolated rabbit uroepithelium was mounted in modified Ussing chambers and mechanically stimulated by applying hydrostatic pressure across the mucosa. Increased hydrostatic pressure led to increased mucosal-to-serosal Na+ absorption across the uroepithelium via the amiloride-sensitive epithelial Na+ channel. In addition to this previously characterized pathway for Na+ absorption, hydrostatic pressure also induced the secretion of Cl- and K+ into the mucosal bathing solution under short-circuit conditions, which was confirmed by a net serosal-to-mucosal flux of 36Cl- and 86Rb+. K+ secretion was likely via a stretch-activated nonselective cation channel sensitive to 100 microM amiloride, 10 mM tetraethylammonium, 3 mM Ba2+, and 1 mM Gd3+. Hydrostatic pressure-induced ion transport in the uroepithelium may play important roles in electrolyte homeostasis, volume regulation, and mechanosensory transduction.

Expression of purinergic receptors in non-melanoma skin cancers and their functional roles in A431 cells

We investigated the use of purinergic receptors as a new treatment modality for nonmelanoma skin cancers. Purinergic receptors, which bind adenosine 5'-tri-phosphate, are expressed on human cutaneous keratinocytes. Previous work in rat and human epidermis suggested functional roles for purinergic receptors in the regulation of proliferation, differentiation, and apoptosis. Immunohistochemical analysis of frozen sections in human basal cell carcinomas and squamous cell carcinomas for P2X5, P2X7, P2Y1, P2Y2, and P2Y4 receptors was performed, accompanied by detailed analysis of archive material of tumor subtypes in paraffin sections. Functional studies were performed using a human cutaneous squamous cell carcinoma cell line (A431), where purinergic receptor subtype agonists were applied to cells and changes in cell number were quantified via a colorimetric assay. Immunostaining in paraffin sections was essentially the same as that in frozen sections, although more detail of the subcellular composition was visible. P2X5 and P2Y2 receptors were heavily expressed in basal cell carcinomas and squamous cell carcinomas. P2X7 receptors were expressed in the necrotic center of nodular basal cell carcinomas and in apoptotic cells in superficial multifocal and infiltrative basal cell carcinomas, and squamous cell carcinomas. P2Y1 receptors were only expressed in the stroma surrounding tumors. P2Y4 receptors were found in basal cell carcinomas but not in squamous cell carcinomas. P2X5 receptors appear to be associated with differentiation. The P2X7 receptor agonist benzoylbenzoyl-adenosine 5'-triphosphate and high concentrations of adenosine 5'-triphosphate (1000-5000 microM) caused a significant reduction in A431 cell number (p<0.001), whereas the P2Y2 receptor agonist uridine 5'-triphosphate caused a significant amount of proliferation (p<0.001). We have demonstrated that non-melanoma skin cancers express functional purinergic receptors and that P2X7 receptor agonists significantly reduce cell numbers in vitro.