AUGMENTED STRETCH ACTIVATED ADENOSINE TRIPHOSPHATE RELEASE FROM BLADDER UROEPITHELIAL CELLS IN PATIENTS WITH INTERSTITIAL CYSTITIS

Pharmacological effects of Hachi-mi-jio-gan extract (Harncare) on the contractile response and on pharmacologically relevant receptors in the rat bladder

Hachi-mi-jio-gan extract (Harncare; HE), a galenical produced from the traditional Chinese herbal mixture Ba-Wei-Die-Huang-Wan, has been reported to improve lower urinary tract symptoms (LUTS) in patients. The present study was undertaken to clarify the pharmacological effects of HE on smooth muscle contraction and on pharmacologically relevant (muscarinic, 1,4-DHP and purinergic) receptors in the rat bladder. Additionally, the effects of repeated oral treatment with HE on the hepatic cytochrome P-450 (CYP) and on blood biochemical values in rats were examined. HE (10 mg/ml) inhibited significantly the acetylcholine-induced contraction of isolated rat bladder strips. The pD(2) value in the absence and presence of HE (10 mg/ml) was 5.14+/-0.16 and 3.99+/-0.17, respectively. HE (0.1 to 10 mg/ml) inhibited the specific binding of [N-methyl-(3)H]scopolamine methyl chloride ([(3)H]NMS), (+)-[(3)H]PN 200-110 and alphabeta-methylene ATP [2,8-(3)H]tetrasodium salt ([(3)H]alphabeta-MeATP) in the rat bladder in a concentration-dependent manner. The respective IC(50) values were 6.85+/-0.94, 7.08+/-0.72 and 1.34+/-0.23 mg/ml. Based on IC(50) values, the binding activity of HE for purinergic receptors was shown to be significantly (about 7 times) greater than that for muscarinic and 1,4-DHP receptors. Repeated oral administration of HE (10, 30 and 100 mg/kg/day) for 4 weeks had little or no effect on the level and activity of hepatic CYP or on blood biochemical values in rats. In conclusion, the present study has shown that HE exerts significant binding activity for pharmacologically relevant receptors in the rat bladder and a relaxant effect on the acetylcholine-induced contraction of isolated muscle strips. HE seemed to exhibit little pharmacokinetic interaction with drugs.

Urothelial signaling

Beyond serving as a simple barrier, there is growing evidence that the urinary bladder urothelium exhibits specialized sensory properties and play a key role in the detection and transmission of both physiological and nociceptive stimuli. These urothelial cells exhibit the ability to sense changes in their extracellular environment including the ability to respond to chemical, mechanical and thermal stimuli that may communicate the state of the urothelial environment to the underlying nervous and muscular systems. Here, we review the specialized anatomy of the urothelium and speculate on possible communication mechanisms from urothelial cells to various cell types within the bladder wall.

A refocus on the bladder as the originator of storage lower urinary tract symptoms: a systematic review of the latest literature

CONTEXT

The focus of clinical understanding and management of male storage lower urinary tract symptoms (LUTS) has shifted from the prostate to the bladder. This is mirrored by an increasing body of experimental evidence suggesting that the bladder is the central organ in the pathogenesis of LUTS.

OBJECTIVE

A systematic review of the literature available on pathophysiologic aspects of storage LUTS.

EVIDENCE ACQUISITION

Medline was searched for the period ending December 2008 for studies on human and animal tissue exploring possible functional and structural alterations underlying bladder dysfunction. Further studies were chosen on the basis of manual searches of reference lists and review papers.

EVIDENCE SYNTHESIS

Numerous recent publications on LUTS pathophysiology were identified. They were grouped into studies exploring abnormalities on urothelial/suburothelial, muscular, or central levels.

CONCLUSIONS

Studies revealed both structural and functional alterations in bladders from patients with LUTS symptoms or animals with experimentally induced bladder dysfunction. In particular, the urothelium and the suburothelial space, containing afferent nerve fibres and interstitial cells, have been found to form a functional unit that is essential in the process of bladder function. Various imbalances within this suburothelial complex have been identified as significant contributors to the generation of storage LUTS, along with potential abnormalities of central function.

Ion channel and receptor mechanisms of bladder afferent nerve sensitivity

Sensory nerves of the urinary bladder consist of small diameter A(delta) and C fibers running in the hypogastic and pelvic nerves. Neuroanatomical studies have revealed a complex neuronal network within the bladder wall. Electrophysiological recordings in vitro and in vivo have revealed several distinct classes of afferent fibers that may signal a wide range of bladder stimulations including physiological bladder filling, noxious distension, cold, chemical irritation and inflammation. The exact mechanisms that underline mechanosensory transduction in bladder afferent terminals remain ambiguous; however, a wide range of ion channels (e.g., TTX-resistant Na(+) channels, Kv channels and hyperpolarization-activated cyclic nucleotide-gated cation channels) and receptors (e.g., TRPV1, TRPM8, TRPA1, P2X(2/3), etc) have been identified at bladder afferent terminals and implicated in the generation and modulation of afferent signals. Experimental investigations have revealed that expression and/or function of these ion channels and receptors may be altered in animal models and patients with overactive and painful bladder disorders. Some of these ion channels and receptors may be potential therapeutic targets for bladder diseases.

Changes in adenosine triphosphate-stimulated ATP release suggest association between cytokine and purinergic signaling in bladder urothelial cells

OBJECTIVES

To determine whether antiproliferative factor (APF) or epidermal growth factor (EGF) can induce changes in purinergic signaling in normal bladder urothelial cells (BUCs) and/or whether antagonizing EGF activity or blocking adenosine triphosphate (ATP)-purinergic receptors can induce changes in purinergic signaling in interstitial cystitis (IC) cells.

METHODS

IC and normal BUCs were obtained from patients' bladder biopsy specimens. IC BUCs were treated with genistein, which antagonizes EGF's activity, and normal BUCs were treated with EGF, mock APF, or APF. Suramin, which antagonizes ATP activity, was used to treat the APF-treated normal BUCs. ATP release was determined by stimulating the BUCs with 30 microM ATP and then collecting the supernatant for a 3-hour period. ATP quantification was measured by luciferin-luciferase assay. Purinergic receptor P2X, ligand-gated ion channel, 3 (P2X3) expression on BUCs was determined by fluorescence-activated cell sorting.

RESULTS

Genistein treatment of IC BUCs resulted in significantly decreased ATP release, thus reverting IC cells to a normal purinergic signaling phenotype. Conversely, normal BUCs treated with EGF or APF resulted in significantly increased ATP release and P2X3 expression, converting normal BUCs to an IC phenotype. Also, suramin treatment of APF-treated normal BUCs significantly reduced ATP release.

CONCLUSIONS

Genistein and suramin reversed the augmented ATP release in IC BUCs and APF-treated normal BUCs, respectively, suggesting the possibility of intravesical use of these agents in IC treatment. EGF and APF induced augmented purinergic signaling in normal BUCs, as determined by increased ATP release and increased P2X3 expression. These data suggest an association between cytokines and purinergic signaling in human BUCs that should be explored further.

Mechanotransduction and chemosensitivity of two major classes of bladder afferents with endings in the vicinity to the urothelium

The guinea pig bladder is innervated by at least five distinct major classes of extrinsic sensory neurons. In this study, we have examined the mechanisms of mechanotransduction and chemosensitivity of two classes of bladder afferents that have their endings in the vicinity of the urothelium: stretch-sensitive muscle-mucosal mechanoreceptors and stretch-insensitive, mucosal high-responding afferents. The non-selective P2 purinoreceptor antagonist pyridoxal phosphate-6-azophenyl-2',4'-disulphonic acid did not affect stretch- or stroking-induced firing of these afferents but significantly reduced the excitatory action of alpha,beta-methylene ATP. Blocking synaptic transmission in Ca(2+)-free solution did not affect stretch-evoked firing but slightly reduced stretch-induced tension responses. Stroking-induced firing of both classes of afferents was also not affected in Ca(2+)-free solution. Of blockers of mechano-gated channels, benzamil (100 microM), but not amiloride (100 microM), Gd(3+) (100 microM) or SKF 96365 (50 microM), inhibited stretch- and stroking-induced firing. Serotonin (100 microM) applied directly onto receptive fields predominantly activated muscle-mucosal afferents. Muscarine (100 microM) and substance P (100 microM) in 24% and 36% cases activated only mucosal high-responding units. Bradykinin (10 microM), but not prostaglandin E2 (10 microM), excites predominantly mucosal units. High (80 mM) K(+) solution activated both afferent classes, but responses of mucosal units were 4 times greater. In contrast to muscle-mucosal units, most mucosal high-responding units were activated by hot Krebs solution (45-46 degrees C), low pH (pH 4) and capsaicin (3 microm). TRPV1 antagonist, capsazepine (10 microM) was without effect on mechanotransduction by mucosal high-responding afferents. The results show that mechanotransduction of these two types of afferents are not dependant upon Ca(2+)-dependent exocytotic release of mediators, or ATP, and it is likely that benzamil-sensitive stretch-activated ion channels on their endings are involved in direct mechanotransduction. The chemosensitivity to agonists and noxious stimuli differs significantly between these two major classes of bladder afferents that reflects their different physiological and pathophysiological roles in the bladder.

Adenosine receptor expression in Escherichia coli-infected and cytokine-stimulated human urinary tract epithelial cells

OBJECTIVE

To assess the expression and regulation of adenosine receptors in unstimulated, uropathogenic Escherichia coli (UPEC)-infected and cytokine-stimulated human urinary tract epithelial cells, and to examine the regulation of interleukin (IL)-6 secretion in response to A(2A) receptor activation.

MATERIALS AND METHODS

Human urinary tract epithelial cells (A498, T24 and RT4) were grown in cell culture and stimulated with a mixture of pro-inflammatory cytokines (CM) or UPEC. The expression of adenosine receptors was evaluated using semiquantitative reverse transcription-polymerase chain reaction (RT-PCR), Western blot analysis and immunocytochemistry. IL-6 secretion was measured with an enzyme-linked immunosorbent assay.

RESULTS

RT-PCR analysis showed the presence of transcripts for the A(1), A(2A) and A(2B) receptor subtypes but not for the A(3) receptor in A498 kidney epithelial cells. The expression of A(2A) receptor mRNA increased in A498 epithelial cells exposed to CM and UPEC, while A(1) and A(2B) receptor transcripts decreased or remained unchanged. Up-regulation of A(2A) receptors was confirmed at the protein level using Western blot analysis and immunocytochemistry. There was also an increase in A(2A) receptor mRNA in human bladder epithelial cells (T24 and RT4) and in mouse bladder uroepithelium in response to cytokines and UPEC. IL-6 secretion in UPEC-infected A498 cells was decreased by 38% when exposed to the A(2A) receptor agonist CGS 21680.

CONCLUSION

Our data showed a subtype-selective plasticity among adenosine receptors in urinary tract epithelial cells in response to UPEC-infection and cytokines. There was a consistent up-regulation of A(2A) receptors in kidney and bladder epithelial cells. Functionally, A(2A) receptor activation reduced UPEC-induced IL-6 secretion. These findings suggest that adenosine might be a previously unrecognized regulator of the mucosal response in urinary tract infection.

Afferent nerve regulation of bladder function in health and disease

The afferent innervation of the urinary bladder consists primarily of small myelinated (Adelta) and unmyelinated (C-fiber) axons that respond to chemical and mechanical stimuli. Immunochemical studies indicate that bladder afferent neurons synthesize several putative neurotransmitters, including neuropeptides, glutamic acid, aspartic acid, and nitric oxide. The afferent neurons also express various types of receptors and ion channels, including transient receptor potential channels, purinergic, muscarinic, endothelin, neurotrophic factor, and estrogen receptors. Patch-clamp recordings in dissociated bladder afferent neurons and recordings of bladder afferent nerve activity have revealed that activation of many of these receptors enhances neuronal excitability. Afferent nerves can respond to chemicals present in urine as well as chemicals released in the bladder wall from nerves, smooth muscle, inflammatory cells, and epithelial cells lining the bladder lumen. Pathological conditions alter the chemical and electrical properties of bladder afferent pathways, leading to urinary urgency, increased voiding frequency, nocturia, urinary incontinence, and pain. Neurotrophic factors have been implicated in the pathophysiological mechanisms underlying the sensitization of bladder afferent nerves. Neurotoxins such as capsaicin, resiniferatoxin, and botulinum neurotoxin that target sensory nerves are useful in treating disorders of the lower urinary tract.

Development, plasticity and modulation of visceral afferents

Visceral pain is the most common reason for doctor visits in the US. Like somatic pain, virtually all visceral pain sensations begin with the activation of primary sensory neurons innervating the viscera and/or the blood vessels associated with these structures. Visceral afferents also play a central role in tissue homeostasis. Recent studies show that in addition to monitoring the state of the viscera, they perform efferent functions through the release of small molecules (e.g. peptides like CGRP) that can drive inflammation, thereby contributing to the development of visceral pathologies (e.g. diabetes Razavi, R., Chan, Y., Afifiyan, F.N., Liu, X.J., Wan, X., Yantha, J., Tsui, H., Tang, L., Tsai, S., Santamaria, P., Driver, J.P., Serreze, D., Salter, M.W., Dosch, H.M., 2006. TRPV1+ sensory neurons control beta cell stress and islet inflammation in autoimmune diabetes, Cell 127 1123-1135). Visceral afferents are heterogeneous with respect to their anatomy, neurochemistry and function. They are also highly plastic in that their cellular environment continuously influences their response properties. This plasticity makes them susceptible to long-term changes that may contribute significantly to the development of persistent pain states such as those associated with irritable bowel syndrome, pancreatitis, and visceral cancers. This review examines recent insights into visceral afferent anatomy and neurochemistry and how neonatal insults can affect the function of these neurons in the adult. New approaches to the treatment of visceral pain, which focus on primary afferents, will also be discussed.

Cell signaling in interstitial cystitis/painful bladder syndrome

Evidence for several types of cell signaling abnormalities has been presented for patients with interstitial cystitis/painful bladder syndrome (IC/PBS), a poorly understood chronic painful bladder disorder for which currently there is no reliable effective therapy. Increases or decreases in various urine cytokines and growth factors have been found in patient specimens, along with abnormal expression of epithelial differentiation markers, growth factors, cell membrane proteins, neurotransmitters, and other cytokines in tissue biopsies and/or explanted bladder cells from IC/PBS patients. Some of the abnormalities found in bladder epithelial cells from IC/PBS patients have been shown to be induced in normal cells by an antiproliferative factor from IC/PBS bladder epithelial cells that binds to a functional cell membrane receptor (CKAP4/p63). Greater understanding of cell signaling events associated with this debilitating disorder may lead to the development of more effective therapies.

PACAP-mediated ATP release from rat urothelium and regulation of PACAP/VIP and receptor mRNA in micturition pathways after cyclophosphamide (CYP)-induced cystitis

Pituitary adenylate cyclase-activating peptide (PACAP) peptides are expressed in micturition pathways, and PACAP expression is regulated by urinary bladder inflammation. Previous physiological studies have demonstrated roles for PACAP27 and PACAP38 in detrusor smooth muscle (DSM) contraction and a PAC1 receptor antagonist reduced cyclophosphamide (CYP)-induced bladder hyperreflexia. To gain insight into PACAP signaling in micturition and regulation with cystitis, receptor characterization by real-time quantitative polymerase chain reaction and physiological assays were performed. PACAP receptors were identified in tissues of rat micturition pathway, including DSM, urothelium (U), and dorsal root ganglia (DRG) after acute (4 h), intermediate (48 h) or chronic (8 days) CYP-induced cystitis. PAC1 messenger RNA expression significantly (p < or = 0.05) increased in U and DSM after 48 h and chronic CYP-induced cystitis after an initial decrease at 4 h. VPAC1 and VPAC2 transcripts increased in U and DSM after acute and intermediate CYP-induced cystitis followed by a decrease in VPAC2 expression with chronic cystitis. Application of PACAP27 (100 nM) to cultured urothelial cells evoked adenosine triphosphate (ATP) release that was blocked by the PAC1 specific antagonist, M65 (1 microM). PACAP38 (100 nM) also evoked ATP release from cultured urothelial cells, but ATP release was less than that observed with PACAP27. PACAP transcripts were increased in the U with intermediate and chronic cystitis, whereas vasoactive intestinal polypeptide (VIP) expression in both tissues was very low and showed no regulation with cystitis. Regulation of PACAP, galanin, and substance P transcripts expression was observed in lumbosacral DRG, but no regulation for VIP was observed. The current data demonstrate PACAP and PAC1 regulation in micturition pathways with inflammation and PACAP-mediated ATP release from urothelium.

The neural control of micturition

Micturition, or urination, occurs involuntarily in infants and young children until the age of 3 to 5 years, after which it is regulated voluntarily. The neural circuitry that controls this process is complex and highly distributed: it involves pathways at many levels of the brain, the spinal cord and the peripheral nervous system and is mediated by multiple neurotransmitters. Diseases or injuries of the nervous system in adults can cause the re-emergence of involuntary or reflex micturition, leading to urinary incontinence. This is a major health problem, especially in those with neurological impairment. Here we review the neural control of micturition and how disruption of this control leads to abnormal storage and release of urine.

Efficacy of a novel device for assessment of autonomic sensory function in the rat bladder

PURPOSE

We developed and tested the efficacy of an implantable bladder device which, when combined with the Neurometer, can be used to assess fiber specific afferent bladder sensation in the rat.

MATERIALS AND METHODS

We developed an implantable bladder device that applies selective nerve fiber stimuli (250 Hz for small myelinated Adelta fibers and 5 Hz for unmyelinated C fibers) to the bladder mucosa in the rat to determine bladder sensory perception threshold values. We performed 3 experiments in 55 female Sprague-Dawley rats to examine the effects of our device on voiding habits, assess the interobserver reliability of the sensory perception threshold and determine the effects of intravesical administration of resiniferatoxin (Sigma) and lidocaine on the sensory perception threshold.

RESULTS

Sensory perception threshold values obtained by 2 blinded, independent observers were not different from each other (p = 0.41). Sensory perception threshold values obtained at the 2 stimulation frequencies remained constant for at least 3 weeks after device implantation. A significant increase in sensory perception threshold values after resiniferatoxin instillation was noted at a stimulus frequency of 5 Hz (p = 0.02), whereas intravesical lidocaine led to an immediate increase in the sensory perception threshold at 250 and 5 Hz. Device implantation led to an early decreased voided volume and increased frequency of voids, although these parameters returned to normal after 4 days.

CONCLUSIONS

Assessment of bladder afferent sensation with our newly developed device is feasible in rats. It provides sensory perception thresholds that appear to be fiber-type selective for autonomic bladder afferent nerves.

The use of botulinum neurotoxin type A (BoNTA) in urology

The use of Botulinum neurotoxin type A (BoNT/A) in the lower urinary tract was pioneered as early as 20 years ago with injections into the urethral sphincter reducing bladder voiding pressures, urethral pressures, and post-void residual urine. Over the past 9 years, the use of BoNT/A has revolutionised the treatment of intractable symptoms associated with the neurogenic or idiopathic overactive bladder, both in adults and children. The duration of clinical improvement is 6-11 months, is accompanied by significant amelioration of patients' quality of life and repeat bladder treatments appear to have sustained effects. Despite evidence for an effect on the afferent pathways, its mode of action in the human bladder remains largely unknown. The use of BoNT/A has also expanded into the painful bladder syndrome and in benign prostatic diseases, with promising preliminary results. This review aims to provide an insight of the use of BoNT/A in the lower urinary tract, addressing issues such as treatment outcomes and safety, mechanisms of action and potential for future research.

Hyaluronan treatment of interstitial cystitis/painful bladder syndrome

The aim of this study is to evaluate the efficacy of intravesical hyaluronan therapy in interstitial cystitis/painful bladder syndrome (IC/PBS). One hundred twenty-six patients with IC/PBS and an average disease duration of 6.1 years were treated with weekly instillations of a 50-cm3 phosphate-buffered saline solution containing 40 mg sodium hyaluronate. To be eligible for hyaluronan treatment, a positive modified potassium test was requested as a sign of a urine-tissue barrier disorder. Data were obtained by a visual analogue scale (VAS) questionnaire rating from 0 to 10 that asked for global bladder symptoms before and after therapy. Additional questions evaluated the therapeutic impact on quality of life. A positive and durable impact of hyaluronan therapy on IC/PBS symptoms was observed--103 (85%) of the patients reported symptom improvement (> or =2 VAS units). The mean initial VAS score of 8.5 decreased to 3.5 after therapy (p < 0.0001). Out of 121 patients, 67 (55%) remained with no or minimal bladder symptoms after therapy (VAS 0-2). The majority (101, 84%) reported significant improvement of their quality of life. Intravesical therapy had to be initiated again with good success in 43 patients (34.5%) as symptoms recurred after discontinuation of treatment, while the rest stayed free of symptoms for up to 5 years. In general, hyaluronan therapy was well tolerated and, with the exception of mild irritative symptoms, no adverse reactions were reported for a total of 1,521 instillations. Timely hyaluronan instillation therapy may lead to complete symptom remission or even cure in part of the IC/PBS patients, while some responders need continuous intravesical therapy. The present results suggest that selection of patients for hyaluronan therapy by potassium testing improves the outcome of intravesical therapy with a response rate of >80%.

Mechanisms by which a phytotherapeutic drug influences bladder activity in rats

PURPOSE

We investigated the mechanisms by which Eviprostat, a phytotherapeutic drug for benign prostatic hyperplasia, influences bladder activity in rats.

MATERIALS AND METHODS

A total of 42 female rats were divided into a control group and an Eviprostat group. Rats in the control group were fed a standard diet, while animals in the Eviprostat group were fed a diet containing 0.1% Eviprostat. After 2 weeks 14 rats (7 rats per group) underwent continuous cystometry with physiological saline or 0.1% acetic acid solution and bladder activity was recorded. Body weight, blood pressure, plasma monoamines and adenosine triphosphate were measured in another 14 rats (7 per group). In the remaining 14 rats (7 per group) 0.1% acetic acid solution was infused into the bladder and urinary adenosine triphosphate was measured before and after stimulation.

RESULTS

During cystometry with acetic acid the interval between bladder contractions was shorter and maximum bladder contraction pressure was higher in the control group compared with results obtained using physiological saline but such differences were not seen in the Eviprostat group. Plasma adrenaline and noradrenaline were lower in the Eviprostat group than the control group but no difference in blood pressure was observed. Urinary adenosine triphosphate was higher in the 2 groups than before stimulation but the increase was smaller in the Eviprostat group than in the control group.

CONCLUSIONS

These results suggest that Eviprostat acts to maintain low catecholamine and also inhibit pathological bladder activity by decreasing adenosine triphosphate release from the bladder.

Cyclophosphamide-induced bladder inflammation sensitizes and enhances P2X receptor function in rat bladder sensory neurons

We studied sensitization of retrogradely labeled bladder sensory neurons and plasticity of P2X receptor function in a model of cystitis using patch-clamp techniques. Saline (control) or cyclophosphamide (CYP) was given intraperitoneally to rats on days 0, 2, and 4. On day 5, lumbosacral (LS, L6-S2) or thoracolumbar (TL, T12-L2) dorsal root ganglia were removed and dissociated. Bladders from CYP-treated rats showed partial loss of the urothelium and greater myeloperoxidase activity compared with controls. Bladder neurons from CYP-treated rats were increased in size (based on whole cell capacitance) compared with controls and exhibited lower activation threshold, increased action potential width, and greater number of action potentials in response to current injection or application of purinergic agonists. Most control LS bladder neurons (>85%) responded to ATP or alpha,beta-metATP with a slowly desensitizing current; these agonists affected only half of TL neurons, producing predominantly fast/mixed desensitizing currents. CYP treatment increased the fraction of TL bladder neurons sensitive to purinergic agonists (>80%) and significantly increased current density in both LS and TL bladder neurons compared with control. Importantly, LS and TL neurons from CYP-treated rats showed a selective increase in the functional expression of heteromeric P2X(2/3) and homomeric P2X(3) receptors, respectively. Although desensitizing kinetics were slower in LS neurons from CYP-treated compared with control rats, recovery kinetics were similar. The present results demonstrate that bladder inflammation sensitizes and increases P2X receptor expression and/or function for both pelvic and lumbar splanchnic pathways, which contribute, in part, to the hypersensitivity associated with cystitis.

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.

Activation of Urothelial Transient Receptor Potential Vanilloid 4 by 4α-Phorbol 12,13-Didecanoate Contributes to Altered Bladder Reflexes in the Rat

The ion channel transient receptor potential vanilloid (TRPV) 4 can be activated by hypo-osmolarity, heat, or certain lipid compounds. Here, we demonstrate expression of functional TRPV4 protein in the urothelium lining the renal pelvis, ureters, urinary bladder, and urethra. Exposure of cultured rat urothelial cells from the urinary bladder to the TRPV4-selective agonist 4alpha-phorbol 12,13-didecanoate (4alpha-PDD) promoted Ca2+ influx, evoked ATP release, and augmented the ATP release evoked by hypo-osmolarity. In awake rats during continuous infusion cystometrograms, intravesical administration of 4alpha-PDD (10-100 microM) increased maximal micturition pressure by 51%, specifically by augmenting the portion of each intravesical pressure wave that follows high-frequency urethral oscillations and voiding. This unusual pharmacological effect was prevented by intravesical pretreatment with the nonselective ATP receptor antagonist, pyridoxal phosphate-6-azophenyl-2',4'-disulfonic acid (100 microM), systemic treatment with the selective P2X3 purinergic antagonist 5-([(3-phenoxybenzyl)[1S)-1,2,3,4-tetrahydro-1-naphthalenyl]amino]carbonyl)-1,2,4-benzenetricarboxylic acid (A317491) (250 micromol/kg), or urethane anesthesia, but was unaffected by capsaicin pretreatment (100 mg/kg s.c.) or denervation of the urethral sphincter. 4Alpha-PDD (1-100 microM) did not alter the contractility to electrical stimulation of excised bladder strips. We conclude that activation of urothelial TRPV4 by 4alpha-PDD and release of mediators such as ATP trigger a novel neural mechanism that regulates the late phase of detrusor muscle contraction after micturition. These data raise the possibility that TRPV4 channels in the urothelium could contribute to abnormal bladder activity.

Future pharmacotherapy in chronic bladder hypersensory conditions

There is a high prevalence of lower urinary tract symptoms (LUTS) in the adult population, afflicting both genders. LUTS can be thought of as a chronic hypersensory condition of the bladder. The treatment of LUTS remains largely empiric based on incomplete understanding of pathophysiology and lack of clinically effective measurement tools. Future treatments for LUTS can target intrinsic physiologic bladder defects, whether they arise from the urothelium, smooth muscle and/or nerves. The bladder and its different compartments can also have pharmacologic agents delivered in the most direct fashion through transurethral catheterization either via catheter or cystoscope. Non-bacterial-induced bladder inflammation and CNS abnormalities may also give rise to LUTS, thus representing other targets for future pharmacotherapy.

Neural Upregulation in Interstitial Cystitis

Interstitial cystitis (IC) is a syndrome of bladder hypersensitivity with symptoms of urgency, frequency, and chronic pelvic pain. Although no consensus has been reached on the underlying cause of IC, several pathophysiologic mechanisms, including epithelial dysfunction, mast cell activation, and neurogenic inflammation, have been proposed. Despite multiple different causes of urinary cystitis, the bladder's response to cystitis is limited and typical. Animal experiments have shown upregulation of proteinase-activated receptors, tryptase, beta-nerve growth factor, inducible nitric oxide synthase, nuclear transcription factor-kappaB, c-Fos, phosphodiesterase 1C, cyclic adenosine monophosphate (cAMP)-dependent protein kinase, and proenkephalin B. After the noxious stimulus has abated, downregulation of genes appears to follow. Distention of the bladder results in the release of adenosine triphosphate (ATP) from urothelial cells, which activates purinergic P2X3 receptors. Activation by ATP of P2X3-expressing afferents is a fundamental signaling factor in bladder sensation and appears to play a role in bladder reflexes. Fos proteins present in spinal cord neurons have been shown to be upregulated in animals that have undergone cyclophosphamide-induced chemical cystitis. These and other findings suggest that neural upregulation occurs both peripherally and centrally in subjects with chronic cystitis. It is unclear whether neural mechanisms and inflammation are the cause of IC or the result of other initiating events. Neural upregulation is known to play a role in the chronicity of pain, urgency, and frequency and represents an exciting area of research that may lead to additional treatments and a better understanding of IC.

Mechanisms of disease: involvement of the urothelium in bladder dysfunction

Although the urinary bladder urothelium has classically been thought of as a passive barrier to ions and solutes, a number of novel properties have been recently attributed to urothelial cells. Studies have revealed that the urothelium is involved in sensory mechanisms (i.e. the ability to express a number of sensor molecules or respond to thermal, mechanical and chemical stimuli) and can release chemical mediators. Localization of afferent nerves next to the urothelium suggests that urothelial cells could be targets for neurotransmitters released from bladder nerves or that chemicals released by urothelial cells could alter afferent nerve excitability. Taken together, these and other findings highlighted in this article suggest a sensory function for the urothelium. Elucidation of mechanisms that influence urothelial function might provide insights into the pathology of bladder dysfunction.

Apical epidermal growth factor receptor signaling: regulation of stretch-dependent exocytosis in bladder umbrella cells

The apical surface of polarized epithelial cells receives input from mediators, growth factors, and mechanical stimuli. How these stimuli are coordinated to regulate complex cellular functions such as polarized membrane traffic is not understood. We analyzed the requirement for growth factor signaling and mechanical stimuli in umbrella cells, which line the mucosal surface of the bladder and dynamically insert and remove apical membrane in response to stretch. We observed that stretch-stimulated exocytosis required apical epidermal growth factor (EGF) receptor activation and that activation occurred in an autocrine manner downstream of heparin-binding EGF-like growth factor precursor cleavage. Long-term changes in apical exocytosis depended on protein synthesis, which occurred upon EGF receptor-dependent activation of mitogen-activated protein kinase signaling. Our results indicate a novel physiological role for the EGF receptor that couples upstream mechanical stimuli to downstream apical EGF receptor activation that may regulate apical surface area changes during bladder filling.

Purinoceptors as therapeutic targets for lower urinary tract dysfunction

Lower urinary tract symptoms (LUTS) are present in many common urological syndromes. However, their current suboptimal management by muscarinic and alpha(1)-adrenoceptor antagonists leaves a significant opportunity for the discovery and development of superior medicines. As potential targets for such therapeutics, purinoceptors have emerged over the last two decades from investigations that have established a prominent role for ATP in the regulation of urinary bladder function under normal and pathophysiological conditions. In particular, evidence suggests that ATP signaling via P2X(1) receptors participates in the efferent control of detrusor smooth muscle excitability, and that this function may be heightened in disease and aging. ATP also appears to be involved in bladder sensation, via activation of P2X(3) and P2X(2/3) receptors on sensory afferent neurons, both within the bladder itself and possibly at central synapses. Such findings are based on results from classical pharmacological and localization studies in non-human and human tissues, knockout mice, and studies using recently identified pharmacological antagonists--some of which possess attributes that offer the potential for optimization into candidate drug molecules. Based on recent advances in this field, it is clearly possible that the development of selective antagonists for these receptors will occur that could lead to therapies offering better relief of sensory and motor symptoms for patients, while minimizing the systemic side effects that limit current medicines.

Dysfunction of bladder urothelium and bladder urothelial cells in interstitial cystitis

The human bladder urothelium (BU) and bladder urothelial cells (BUCs) play an important role in the normal functioning of bladder including bladder storage. Current evidence in interstitial cystitis (IC) supports multiple abnormalities in bladder urothelial physiology. These data have come primarily from human studies. The discovery of a novel protein termed the antiproliferative factor (APF) uniquely expressed by IC BUCs is extremely important. APF induces increased permeability of normal BUCs grown in culture. Furthermore, APF regulates expression of other cytokines, including upregulating heparin-binding epidermal growth factor-like growth factor and downregulating epidermal growth factor by BUCs. These cytokine abnormalities were also related to increases in purinergic (adenosine triphosphate) signaling, which could mediate increased bladder sensation. Recent studies of uroplakins, which are specialized proteins expressed only in the apical urothelial cells, suggest that uroplakins play a role in the barrier function of the BU. It is also conceivable that alterations in uroplakins may result in bladder symptoms related to increased permeability or decreased protective function. As the body of knowledge about BU and BUC function increases, novel therapies targeting urothelial cells should become clinically feasible.

Urinary bladder urothelium: Molecular sensors of chemical/thermal/mechanical stimuli

The identification of functional receptors/ion channels in bladder urothelial cells and the involvement of these sensor molecules in the release of chemical mediators (nitric oxide, NO; ATP) suggest that urothelial cells exhibit specialized sensory and signaling properties. Such mechanisms could allow these cells to respond to their chemical and physical environments and to engage in reciprocal communication with neighboring urothelial cells as well as nerves in the bladder wall. These and other findings highlight the functional importance of the urinary bladder urothelium and suggest that perturbations in urothelial targets and/or cell-cell interactions may lead to a number of urinary tract abnormalities.

Mechanisms of disease: role of purinergic signaling in the pathophysiology of bladder dysfunction

Although the 'purinergic nerve hypothesis' proposed by Burnstock in the early 1970s was met with considerable skepticism, it is now accepted that certain neurons use a purine nucleotide or nucleoside such as ATP or adenosine as a neurotransmitter. Likewise, early studies indicated that the human bladder is devoid of purinergic nerves mediating contraction; however, later studies demonstrated that purinergic nerve-mediated bladder contraction is increased in pathologic conditions such as interstitial cystitis. Cloning and sequencing studies have revealed four subtypes of adenosine receptors and eight subtypes of P2Y receptors, all of which are G-protein-coupled receptors. There are no reports of the cellular location of these receptors in the human bladder. P2X receptors are ligand-gated ion channels, and seven subunits have been cloned and sequenced. Immunohistochemical studies have determined that P2X(1,2,4) subunits are on detrusor-muscle cells, P2X(1-3,5) subunits are on bladder nerves and P2X(2,3,5) subunits are on bladder urothelial cells. Development of purinergic antagonist drugs with selectivity for P2X(1) receptors on detrusor muscle cells might be useful for treatment of detrusor overactivity. Antagonists with selectivity for P2X(3) receptors on bladder sensory nerves might be clinically beneficial for treatment of urinary urgency, and perhaps chronic pelvic pain.

EGF and HB-EGF modulate inward potassium current in human bladder urothelial cells from normal and interstitial cystitis patients

Interstitial cystitis (IC) is an idiopathic condition characterized by bladder hyperalgesia. Studies have shown cytokine and purinergic signaling abnormalities in cultured bladder urothelial cells (BUC) from IC patients. We performed single-cell electrophysiological studies in both normal and IC BUC. A strongly inward rectifying potassium current with conductance of the Kir2.1 channel was identified in normal BUC. This current was significantly reduced in IC BUC. Kir2.1 protein and mRNA were detected in both IC and normal BUC. Epidermal growth factor (EGF) caused a dose-dependent decrease in the inward potassium current in normal BUC. EGF is secreted in higher amounts by IC BUC and is known to decrease Kir2.1 conductance by phosphorylation of Kir2.1. Genistein, a nonspecific phosphorylation inhibitor, increased the inward potassium current in IC BUC and blocked the effect of EGF on normal BUC. Treatment of IC BUC with heparin-binding epidermal growth factor-like growth factor (HB-EGF), previously shown to be secreted in lower amounts by IC BUC, significantly increased inward potassium current. These data show that the inward potassium current in BUC can be modulated by EGF and HB-EGF. Changes in BUC membrane potassium conductance caused by altered levels of EGF and HB-EGF may therefore play a role in the pathophysiology of IC.

Symposium Report on Urothelial Dysfunction: Pathophysiology and Novel Therapies

PURPOSE

The basic premise of this symposium (Workshop 7) at the 2004 International Continence Society meeting in Paris was to elucidate different mechanisms of urothelial cell pathology, explore their impact on bladder function and discuss novel therapeutic interventions.

RESULTS

The topics included 1) urothelial structure and function, 2) the role of adenosine triphosphate in urothelial signaling and cystitis, 3) lamina propria myofibroblasts and purinergic receptors, 4) antiproliferative factor involvement in interstitial cystitis, 5) the urothelium as a reservoir for bacterial infections, 6) radiation cystitis, nitric oxide and gene therapy, and 7) intravesical treatments.

DISCUSSION

It was agreed that the urothelium can no longer be regarded merely as a passive barrier separating urine from the underlying tissues. The epithelial cells of the urothelium form part of an integrated network that also includes afferent and possibly efferent nerves, and suburothelial myofibroblasts. It has a central role in several functions, including bladder wall sensation, local blood flow modulation, pathogen removal and active barrier provision. These functions are achieved through several autocrine and paracrine pathways that involve transmitter release from the urothelium and its ability to integrate incoming signals through its battery of membrane receptors. Several pathological processes were discussed using this knowledge, including the role of small glycoproteins released during interstitial cystitis, the molecular basis of radiation induced urothelial damage, the origin of recurrent urinary tract infections and the mode of action of potential intravesical treatments for overactive bladder.

CONCLUSIONS

Overall it was concluded that the urothelium has a key role in regulating lower urinary tract physiology and pathology.

New theories in interstitial cystitis

Interstitial cystitis (IC) is a chronic symptom-complex characterized by pathological sensation of the bladder (i.e. bladder pain in addition to augmented sensory signals such as urinary frequency and urgency) without evidence of bacterial cystitis or other identifiable lower urinary tract disease. Patients with IC typically describe feeling the urge to void frequently, as well as pain in the bladder and/or urethra. The painful sensation may be described as burning, pressure, sharp, or aching, and is often difficult for the patient to localize precisely. Multiple theories as to the cause of IC have been proposed with varying degrees of evidence. The current body of literature supports the idea that IC is associated with an intrinsic pathology of the bladder urothelial cells. The identification and complete characterization of antiproliferative factor (APF), which is uniquely expressed by urothelial cells in bladders affected by IC, are major advances in the understanding of IC. Additionally, urothelial cells have been likened to neurons because of their ability to express neuronal receptors and release neurotransmitters. The purinergic pathway has been shown to be upregulated in urothelial cells in bladders affected by IC. These new findings should help to direct the development of newer clinical treatments for IC. A complete understanding of IC will only be possible with parallel advances in both basic and clinical sciences.

Kinetics of urothelial ATP release

Recent reports have proposed that the urothelium can sense mechanical stretch and communicate this information to sensory afferent neurons by the release of ATP into the vicinity of P2X-containing neurons. This report investigates the bidirectional release of ATP by in vitro rabbit urothelium. ATP was measured using the luciferin-luciferase assay. Immediately after washing of both sides of the epithelium, there was a linear increase in ATP content in the mucosal compartment with a rate of 23 +/- 6.5 fmol x min(-1) x cm(-2) (n = 18). Serosal ATP content increased as a saturating exponential function, suggesting a constant rate of release and degradation of ATP by ectonucleotidases/exonucleotidases. The presence of a serosal ectonucleotidase/exonucleotidases was demonstrated by the time-dependent decrease in exogenously added ATP. The maximum rate of hydrolysis was 11 pmol x min(-1) x cm(-2) with a K(m) of 0.49 microM. The time course of serosal ATP release was modeled as a constant rate of release (d: mol x min(-1) x cm(-2)) and rate constant of hydrolysis (k(h): min(-)). In control conditions d was 18 fmol x min(-1) x cm(-2) and k(h) of 0.056 +/- 0.01 min(-) (n = 18). Steady-state serosal chamber content is 370 +/- 90 fmol/cm(2), and concentration is 50 +/- 1.2 x 10(-12) M. Stretching the tissue resulted in a transient fivefold increase in the rate of mucosal ATP release and a transient sixfold increase in serosal ATP release. Half-osmotic strength solutions increased mucosal release by 10-fold and serosal release by 5-fold. Tissue damage resulted in a step-increase in mucosal chamber ATP content by 6.6 +/- 1 pmol/cm(2) and serosal chamber ATP by 0.1 +/- 0.06 pmol/cm(2) (n = 5).

Botulinum A Toxin Intravesical Injections in the Treatment of Painful Bladder Syndrome: A Pilot Study

OBJECTIVE

We evaluated the efficacy and tolerability of botulinum A toxin (BTX-A) intravesical injections in patients affected by painful bladder syndrome with increased urinary frequency, refractory to conventional treatment modalities.

METHODS

Twelve women and two men were prospectively included in the study. Under short general anaesthesia patients were given injections of 200 U of commercially available BTX-A diluted in 20 ml 0.9% NaCl. Injections were performed submucosally in the trigone and bladder floor under cystoscopic control. Voiding chart, the Visual Analog Scale (VAS) for pain, and urodynamics were performed before treatment and 1 and 3 mo afterward.

RESULTS

Overall, 12 patients (85.7%) reported subjective improvement at 1 and 3 mo follow-up. The mean VAS score was significantly reduced at 1 and 3 mo after treatment (p<0.05 for both); at the same time points daytime and nighttime urinary frequency significantly decreased (p<0.01 and p<0.05, respectively), and bladder cystometric capacity significantly increased (p<0.01). Two patients reported incomplete bladder emptying. We did not detect any systemic side effects during or after treatment.

CONCLUSIONS

The results of this pilot study indicate that BTX-A intravesical injections are effective in the short-term management of painful bladder syndrome. By modulating afferent C-fiber activity within the bladder walls, BTX-A significantly improves urodynamic parameters and reduces bladder pain and urinary frequency.

Characterization of adenosine receptors in the human bladder carcinoma T24 cell line

The molecular and pharmacological properties of adenosine receptors in the T24 human bladder epithelial carcinoma cell line were assessed by Reverse Transcriptase-Polymerase Chain Reaction (RT-PCR), Ca2+ Flux, cAMP production and interleukin-8 measurements. RT-PCR experiments detected the presence of transcripts for the adenosine A1, A2A and A2B receptors but not for the adenosine A3 subtype. Application of specific adenosine receptor ligands resulted in concentration-dependent increases in intracellular calcium ([Ca2+]i) with the following order of potency and EC50 values: 5'-N-Ethylcarboxamidoadenosine (NECA) (1153+/-214)>5'-(N-Cyclopropyl)carboxamidoadenosine (CPCA) (1436+/-186)>adenosine (4823+/-932). This rank order of potency is typical of adenosine A2B receptors. In addition, select adenosine receptor antagonists N-(4-acetylphenyl)-2-[4-(2,3,6,7-tetrahydro-2,6 dioxo-1,3-dipropyl-1H-purin-8-yl)phenoxy]acetamide (MRS 1706), 8-[4-[((4-Cyano[2,6-]-phenyl)carbamoylmethyl)oxy]phenyl]-1,3-di(n-propyl)-xanthine (MRS 1754), 1,3-Diethyl-8-phenylxanthine (DPCPX), 1,3-Diethyl-8-phenylxanthine (DPX), Alloxazine, 8-(3-Chlorostyryl)caffeine (CSC), and Theophylline blocked the NECA-induced calcium responses. Additionally, NECA, CPCA, and adenosine stimulated cAMP formation with a rank order of potency characteristic of adenosine A2B receptors. The select adenosine A2A antagonist, 5-amino-7-(phenylethyl)-2-(2-furyl)-pyrazolo[4,3-e]-1,2,4-triazolo[1,5-c] pyrimidine (SCH 58261) failed to antagonize the NECA response, whereas the potent and highly selective adenosine A2B antagonists MRS 1754 and MRS 1706 inhibited NECA-stimulated cAMP production. Lastly, NECA-induced interleukin-8 secretion was inhibited by MRS 1754. Taken together, these data indicate that [Ca2+]i accumulation and cAMP production as well as interleukin-8 secretion is mediated through the adenosine A2B receptor in the T24 cell line.

Interstitial Cystitis Versus Detrusor Overactivity: A Comparative, Randomized, Controlled Study of Cystometry Using Saline and 0.3 M Potassium Chloride

PURPOSE

We compared cystometric findings in interstitial cystitis and detrusor overactivity using 0.3 M KCl and 0.9% normal saline.

MATERIALS AND METHODS

Female patients with established diagnoses of IC (7 patients according to NIDDK criteria) and urodynamically proven DO (10 patients) underwent consecutive cystometrograms using 0.9% normal saline and 0.3 M KCl, the order of which was randomized for each patient. Individual CMGs were performed by separate investigators, and patients and investigators were blinded to the order in which the solutions were used and to the results of the other CMG. The results were analyzed on a comparative basis using a 2-tailed t test for comparison of the means and a Kolmogorov-Smirnov z test was used for group comparison. A ROC curve was used to plot sensitivity to the false-positive rate.

RESULTS

Irrespective of the diagnosis or the type of infusion used, the volume at FDV was slightly lower with the first CMG compared to the second (mean 76.1 vs 94.2 ml) but did not reach statistical significance (p = 0.20). However, Cmax was similar for first and second CMGs (mean 214 vs 213.2 ml, p = 0.98). Although lower with KCl, there was no significant difference in FDVs obtained with either solution (mean 78.2 vs 92.2 ml for KCl and NS, respectively, p = 0.33). However, KCl produced a significant reduction in Cmax across the whole group (mean 244.5 vs 182.7 ml, p = 0.008). This was most marked in the DO group in which there was a 23% reduction in Cmax with KCl compared to NS, while the IC group showed only a 15% reduction in mean Cmax. The ROC curve, comparing Cmax values for NS with KCl cutoff values of 15% and 30%, resulted in poor positive predictive values (51% and 66%, respectively) for comparative cystometry in distinguishing IC from DO.

CONCLUSIONS

The 0.3 M KCl reduces Cmax in IC and DO, the effect being more pronounced in DO. Urothelial hyperpermeability is not specific to IC. Comparative cystometry using NS and 0.3 M KCl does not help to differentiate IC from DO.

Integrative control of the lower urinary tract: preclinical perspective

Storage and periodic expulsion of urine is regulated by a neural control system in the brain and spinal cord that coordinates the reciprocal activity of two functional units in the lower urinary tract (LUT): (a) a reservoir (the urinary bladder) and (b) an outlet (bladder neck, urethra and striated muscles of the urethral sphincter). Control of the bladder and urethral outlet is dependent on three sets of peripheral nerves: parasympathetic, sympathetic and somatic nerves that contain afferent as well as efferent pathways. Afferent neurons innervating the bladder have A-delta or C-fibre axons. Urine storage reflexes are organized in the spinal cord, whereas voiding reflexes are mediated by a spinobulbospinal pathway passing through a coordination centre (the pontine micturition centre) located in the brainstem. Storage and voiding reflexes are activated by mechanosensitive A-delta afferents that respond to bladder distension. Many neurotransmitters including acetylcholine, norepinephrine, dopamine, serotonin, excitatory and inhibitory amino acids, adenosine triphosphate, nitric oxide and neuropeptides are involved in the neural control of the LUT. Injuries or diseases of the nervous system as well as disorders of the peripheral organs can produce LUT dysfunctions including: (1) urinary frequency, urgency and incontinence or (2) inefficient voiding and urinary retention. Neurogenic detrusor overactivity is triggered by C-fibre bladder afferent axons, many of which terminate in the close proximity to the urothelium. The urothelial cells exhibit 'neuron-like' properties that allow them to respond to mechanical and chemical stimuli and to release transmitters that can modulate the activity of afferent nerves.

Detrusor overactivity induced by intravesical application of adenosine 5'-triphosphate under different delivery conditions in rats

OBJECTIVES

To investigate the effects of intravesical application of adenosine 5'-triphosphate (ATP) on bladder activity to elucidate the role of urothelial barrier function and ecto-ATPase activity in the ATP-mediated mechanism inducing detrusor overactivity.

METHODS

Continuous cystometry by an intravesical catheter inserted from the bladder dome was performed in conscious female rats.

RESULTS

ATP solutions adjusted to pH 6.0 did not elicit significant detrusor overactivity at a concentration of 60 mM. However, in bladders pretreated with protamine sulfate (10 mg/mL) to increase urothelial permeability, ATP solution (pH 6.0) induced detrusor overactivity by decreasing the intercontraction intervals. These irritant effects of ATP after protamine treatment were antagonized by P2X receptor antagonists, such as pyridoxal-5-phosphate-6-azophenyl-2',4'-disulfonic acid (70 micromol/kg) and 2',3'-O-(2,4,6, trinitrophenyl) ATP (30 micromol/kg). These were also suppressed in rats pretreated with systemic capsaicin (125 mg/kg subcutaneously). Alpha,beta-methylene ATP (5 mM, pH 6.0) or ATP (60 mM, pH6) after intravesical infusion of 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (5 mM, pH 6.0), an ecto-ATPase inhibitor, induced detrusor overactivity without protamine pretreatment, but the reduction in intercontraction intervals was smaller compared with that with ATP after protamine treatment.

CONCLUSIONS

Low permeability of bladder epithelium and ecto-ATPase activity can prevent ATP activation of subepithelial P2X receptors to induce bladder overactivity. Thus, enhanced penetration of endogenous ATP owing to urothelial damage may contribute to urinary frequency and bladder pain in hypersensitive bladder disorders such as interstitial cystitis.

A double-blind, randomized controlled trial of cystometry using saline versus 0.3 M potassium chloride infusion in women with overactive bladder syndrome

AIM

To evaluate the effect of 0.3 M potassium chloride on cystometric parameters by comparing it with normal saline as a filling solution in women with overactive bladder (OAB).

PATIENTS AND METHODS

Twenty-three women with significant OAB symptoms underwent consecutive cystometrograms (CMGs) using 0.9% normal saline (NS) and 0.3 M potassium chloride (KCl), the order of which was randomized for each patient. Individual CMGs were performed by separate investigators and both patients and investigators were blinded to the order in which each solution was given and to the results of the other CMG.

RESULTS

Regardless of the nature of the filling solution, the order in which the CMGs were performed had little influence on either first desire to void (FDV, mean 83.5 ml vs. 117.8 ml for first and second CMGs respectively, P = 0.10) or on maximum cystometric capacity (Cmax, mean 265.0 ml vs. 264.4 ml, P = 0.98). KCl produced a significant (24%) reduction in mean Cmax compared to NS (mean 228.6 ml vs. 300.8 ml, P = 0.001), irrespective of the order of infusion.

CONCLUSION

This comparative study using 0.3 M KCl versus NS as filling solutions suggests that intravesical potassium may not simply act on urothelial sensory nerve endings; it may also stimulate detrusor muscle contraction. These findings may influence the interpretation of the potassium sensitivity test in patients with OAB symptoms, particularly in those suspected of having interstitial cystitis.

Role of the urothelium in urinary bladder dysfunction following spinal cord injury

A consequence of spinal cord injury is a change in bladder reflex pathways resulting in the emergence of detrusor hyperreflexia and increased activity of the urethral sphincter. A basis for some of these alterations could be changes in the environment of bladder sensory nerve endings at the target organ. Recent evidence suggests that the urothelium (the lining of the urinary bladder) plays a prominent role in modulating bladder sensory nerve ending excitability. It is conceivable that factors and processes affecting the plasticity of bladder neurons after spinal cord injury may be partly due to changes occurring in the urothelium. Although the urothelium has classically been thought of as a passive barrier to ions/solutes, a number of novel properties have been recently attributed to these cells. Our work and that of others clearly demonstrates that the urothelium exhibits both "sensor" (expression of sensor molecules or response to thermal, mechanical and chemical stimuli) as well as "transducer" (release of factors/transmitters) properties. Taken together, these and other findings discussed in this chapter suggest a sensory function for the urothelium and that alterations in urothelial properties may contribute to afferent abnormalities following spinal cord injury.

Effect of botulinum toxin on detrusor overactivity induced by intravesical adenosine triphosphate and capsaicin in a rat model

OBJECTIVES

To assess the effects of intravesical injection of botulinum toxin type A (BTX) on a model of detrusor overactivity induced by intravesical infusions of adenosine triphosphate (ATP) and capsaicin. BTX has recently been used clinically to treat overactive bladder syndromes without a precise knowledge of the mechanism of action.

METHODS

Twelve Sprague-Dawley rats underwent BTX injections. Six received 1.0 U and 6 received 0.5 U. BTX injections were done at bladder tube placement. Ten rats received saline injections as controls. After 48 hours of recovery, all 22 animals underwent awake, conscious cystometrography (CMG), performed using both saline and ATP (20 mM) intravesical infusion at 0.074 mL/min. In another 4 rats, capsaicin (100 microM) was infused intravesically before and after the BTX injections. The CMG parameters calculated included bladder contraction pressures and contraction frequencies (contractions per minute or Herz).

RESULTS

Intravesical saline CMG produced a contraction frequency of 0.78 +/- 0.10 Hz. Intravesical ATP doubled this voiding frequency to 1.45 +/- 0.18 Hz (P = 0.003). BTX treatment at 1.0 U reduced the frequency to 0.91 +/- 0.13 Hz (P = 0.02). BTX injection significantly decreased the bladder contraction pressure during saline and ATP CMG. However, 0.5 U BTX did not decrease ATP-induced overactivity; therefore, in the capsaicin experiments, 1.0 U BTX was used. Although BTX tended to reverse detrusor overactivity secondary to intravesical capsaicin, this difference was not statistically significant.

CONCLUSIONS

Intravesical infusion of either ATP or capsaicin can induce detrusor overactivity. BTX was more effective in blocking the effect of ATP than of capsaicin, although BTX injection did show a trend in reducing the contraction frequencies and amplitudes induced by capsaicin. The clinical utility of using BTX to treat overactive bladder syndromes and bladder hypersensory states, especially those that may be caused by an augmentation of the purinergic pathway, should be studied further.

P2X2 and P2X3 receptor expression in postnatal and adult rat urinary bladder and lumbosacral spinal cord

P2X receptors mediate the effects of ATP in micturition and nociception. During postnatal maturation, a spinobulbospinal reflex and voluntary voiding replace primitive voiding reflexes. This may involve changes in neuroactive compounds and receptors in bladder reflex pathways. We examined P2X2 and P2X3 receptors in bladder and spinal cord from postnatal (P0-P36, indicating number of days) and adult Wistar rats. Western blot of whole bladders for P2X2 and P2X3 expression was performed. Immunostaining for P2X2 and P2X3 receptors in urothelium and detrusor smooth muscle whole mounts and spinal cord sections was examined. Western blot demonstrated an age-dependent decrease (R(2) = 0.96, P Collapse

Key Words

• postnatal development
• micturition reflexes
• sacral parasympathetic nucleus
• dorsal commissure
• dorsal horn

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MESH Headings

• Aging/metabolism
• Animals
• Female
• Lumbosacral Region
• Male
• Rats
• Rats, Wistar
• Receptors, Purinergic P2/metabolism
• Receptors, Purinergic P2X2
• Receptors, Purinergic P2X3
• Spinal Cord/metabolism
• Tissue Distribution
• Urinary Bladder/metabolism

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Grants

• DK-060481 NIDDK NIH HHS
• NS-040796 NINDS NIH HHS
• R01 DK065989 NIDDK NIH HHS
• R56 DK060481 NIDDK NIH HHS
• R29 DK051369 NIDDK NIH HHS
• DK-065989 NIDDK NIH HHS
• R01 DK060481 NIDDK NIH HHS
• R01 NS040796 NINDS NIH HHS
• DK-051369 NIDDK NIH HHS
• R01 DK051369 NIDDK NIH HHS

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Affiliation(s)

Simon Studeny Department of Neurology, Anatomy and
Ali Torabi Department of Neurology, Anatomy and
Margaret A. Vizzard Department of Neurology, Anatomy and Neurobiology, University of Vermont, College of Medicine, Burlington, Vermont, VT 05405

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More than just a barrier: urothelium as a drug target for urinary bladder pain

Although the urinary bladder urothelium has classically been thought of as a passive barrier to ions/solutes, a number of novel properties have been recently attributed to these cells. Studies have revealed that the urothelium is involved in sensory mechanisms (i.e., ability to express a number of sensor molecules or respond to thermal, mechanical, and chemical stimuli) and can release chemical mediators. Localization of afferent nerves next to the urothelium suggests these cells may be targets for transmitters released from bladder nerves or that chemicals released by urothelial cells may alter afferent excitability. Taken together, these and other findings highlighted in this review suggest a sensory function for the urothelium. Elucidation of mechanisms impacting on urothelial function may provide insights into the pathology of bladder dysfunction.

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.

Two pathways for ATP release from host cells in enteropathogenic Escherichia coli infection

We previously reported that enteropathogenic Escherichia coli (EPEC) infection triggered a large release of ATP from the host cell that was correlated with and dependent on EPEC-induced killing of the host cell. We noted, however, that under some circumstances, EPEC-induced ATP release exceeded that which could be accounted for on the basis of host cell killing. For example, EPEC-induced ATP release was potentiated by noncytotoxic agents that elevate host cell cAMP, such as forskolin and cholera toxin, and by exposure to hypotonic medium. These findings and the performance of the EPEC espF mutant led us to hypothesize that the CFTR plays a role in EPEC-induced ATP release that is independent of cell death. We report the results of experiments using specific, cell-permeable CFTR activators and inhibitors, as well as transfection of the CFTR into non-CFTR-expressing cell lines, which incriminate the CFTR as a second pathway for ATP release from host cells. Increased ATP release via CFTR is not accompanied by an increase in EPEC adherence to transfected cells. The CFTR-dependent ATP release pathway becomes activated endogenously later in EPEC infection, and this activation is mediated, at least in part, by generation of extracellular adenosine from the breakdown of released ATP.

ATP and purinergic receptor-dependent membrane traffic in bladder umbrella cells

The umbrella cells that line the bladder are mechanosensitive, and bladder filling increases the apical surface area of these cells; however, the upstream signals that regulate this process are unknown. Increased pressure stimulated ATP release from the isolated uroepithelium of rabbit bladders, which was blocked by inhibitors of vesicular transport, connexin hemichannels, ABC protein family members, and nucleoside transporters. Pressure-induced increases in membrane capacitance (a measure of apical plasma membrane surface area where 1 microF approximately equals 1 cm2) were inhibited by the serosal, but not mucosal, addition of apyrase or the purinergic receptor antagonist PPADS. Upon addition of purinergic receptor agonists, increased capacitance was observed even in the absence of pressure. Moreover, knockout mice lacking expression of P2X2 and/or P2X3 receptors failed to show increases in apical surface area when exposed to hydrostatic pressure. Treatments that prevented release of Ca2+ from intracellular stores or activation of PKA blocked ATPgammaS-stimulated changes in capacitance. These results indicate that increased hydrostatic pressure stimulates release of ATP from the uroepithelium and that upon binding to P2X and possibly P2Y receptors on the umbrella cell, downstream Ca2+ and PKA second messenger cascades may act to stimulate membrane insertion at the apical pole of these cells.