Expression of muscarinic and nicotinic acetylcholine receptors in the mouse urothelium

Intracellular signaling pathways of muscarinic acetylcholine receptor-mediated detrusor muscle contractions

Acetylcholine plays an essential role in the regulation of detrusor muscle contractions, and antimuscarinics are widely used in the management of overactive bladder syndrome. However, several adverse effects limit their application and patients' compliance. Thus, this study aimed to further analyze the signal transduction of M2 and M3 receptors in the murine urinary bladder to eventually find more specific therapeutic targets. Experiments were performed on adult male wild-type, M2, M3, M2/M3, or Gαq/11 knockout (KO), and pertussis toxin (PTX)-treated mice. Contraction force and RhoA activity were measured in the urinary bladder smooth muscle (UBSM). Our results indicate that carbamoylcholine (CCh)-induced contractions were associated with increased activity of RhoA and were reduced in the presence of the Rho-associated kinase (ROCK) inhibitor Y-27632 in UBSM. CCh-evoked contractile responses and RhoA activation were markedly reduced in detrusor strips lacking either M2 or M3 receptors and abolished in M2/M3 KO mice. Inhibition of Gαi-coupled signaling by PTX treatment shifted the concentration-response curve of CCh to the right and diminished RhoA activation. CCh-induced contractile responses were markedly decreased in Gαq/11 KO mice; however, RhoA activation was unaffected. In conclusion, cholinergic detrusor contraction and RhoA activation are mediated by both M2 and M3 receptors. Furthermore, whereas both Gαi and Gαq/11 proteins mediate UBSM contraction, the activation at the RhoA-ROCK pathway appears to be linked specifically to Gαi. These findings may aid the identification of more specific therapeutic targets for bladder dysfunctions.NEW & NOTEWORTHY Muscarinic acetylcholine receptors are of utmost importance in physiological regulation of micturition and also in the development of voiding disorders. We demonstrate that the RhoA-Rho-associated kinase (ROCK) pathway plays a crucial role in contractions induced by cholinergic stimulation in detrusor muscle. Activation of RhoA is mediated by both M2 and M3 receptors as well as by Gi but not Gq/11 proteins. The Gi-RhoA-ROCK pathway may provide a novel therapeutic target for overactive voiding disorders.

Recessive CHRM5 variant as a potential cause of neurogenic bladder

Neurogenic bladder is caused by disruption of neuronal pathways regulating bladder relaxation and contraction. In severe cases, neurogenic bladder can lead to vesicoureteral reflux, hydroureter, and chronic kidney disease. These complications overlap with manifestations of congenital anomalies of the kidney and urinary tract (CAKUT). To identify novel monogenic causes of neurogenic bladder, we applied exome sequencing (ES) to our cohort of families with CAKUT. By ES, we have identified a homozygous missense variant (p.Gln184Arg) in CHRM5 (cholinergic receptor, muscarinic, 5) in a patient with neurogenic bladder and secondary complications of CAKUT. CHRM5 codes for a seven transmembrane-spanning G-protein-coupled muscarinic acetylcholine receptor. CHRM5 is shown to be expressed in murine and human bladder walls and is reported to cause bladder overactivity in Chrm5 knockout mice. We investigated CHRM5 as a potential novel candidate gene for neurogenic bladder with secondary complications of CAKUT. CHRM5 is similar to the cholinergic bladder neuron receptor CHRNA3, which Mann et al. published as the first monogenic cause of neurogenic bladder. However, functional in vitro studies did not reveal evidence to strengthen the status as a candidate gene. Discovering additional families with CHRM5 variants could help to further assess the genes' candidate status.

Mirabegron and solifenacin are effective for the management of the increased urinary frequency induced by psychological stress in female mice

Evidence to support the effectiveness of β3-adrenoceptor agonist mirabegron and anti-muscarinic solifenacin in the management of bladder dysfunction caused by psychological stress is lacking. This study investigates whether mirabegron or solifenacin reduces the bladder overactivity caused by water avoidance stress (WAS) in mice. Female mice were exposed to WAS for 1 h/day for 10 days and received either placebo, solifenacin or mirabegron in drinking water. Controls were age-matched without stress exposure. Voiding behaviour and functional isolated whole bladder responses during distension and in response to pharmacological agents and electrical field stimulation was investigated. Urinary frequency was significantly increased following stress. Mice treated with mirabegron or solifenacin displayed significantly fewer voiding events compared to the stressed mice, and voiding frequency in drug-treated animals was comparable to unstressed controls. The maximal contractile responses of bladders to carbachol were significantly enhanced by stress and reduced by mirabegron but not solifenacin. The frequency of phasic bladder contractions following stimulation with carbachol was significantly enhanced following stress and remained elevated in the mirabegron treated group. However, treatment with solifenacin significantly reduced the frequency of phasic contractions to unstressed control levels. Solifenacin and mirabegron are beneficial in reducing the overall voiding dysfunction caused by WAS in mice.

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.

Methylglyoxal, a Reactive Glucose Metabolite, Induces Bladder Overactivity in Addition to Inflammation in Mice

Diabetic bladder dysfunction (DBD) is one of the most common complication of diabetes. Methylglyoxal (MGO), a highly reactive dicarbonyl compound formed as a by-product of glycolysis, is found at high levels in plasma of diabetic patients. Here, we explored the effects of chronic administration of MGO on micturition pattern (cystometry) and bladder contractility in vitro in healthy male C57/BL6 mice. Methylglyoxal was given at 0.5% in drinking water for 4 weeks. Exposure to MGO led to bladder tissue disorganization, edema of lamina propria, partial loss of urothelium and multiple leukocyte infiltrates. Filling cystometry revealed significant increases of micturition frequency and number of non-voiding contractions (NVCs) in the MGO group, clearly indicating an overactive bladder profile. Bladder contractions induced by electrical-field stimulation (EFS) and carbachol were significantly higher in the MGO group, while the muscarinic M₂ and M₃ mRNA expressions remained unchanged between groups. Additionally, MGO exposure induced upregulation of TRPA1 and down-regulation of TRPV1 and TRPV4 in bladder tissues. Methylglyoxal did not change the mRNA expression of the advanced glycation end products receptor (RAGE), but markedly increased its downstream NF-κB - iNOS signaling. The mRNA expression of cyclooxygenase-2 (COX-2) and reactive-oxygen species (ROS) levels remained unchanged. Altogether, our data show that 4-week MGO intake in mice produces an overactive bladder phenotype in addition to bladder inflammation and increased NF-kB/iNOS signaling. TRPA1 up-regulation and TRPV1/TRPV4 down-regulation may account for the MGO-induced bladder overactivity. Scavengers of MGO could be an option to ameliorate bladder dysfunction in diabetic conditions.

Expression of components of the urothelial cholinergic system in bladder and cultivated primary urothelial cells of the pig

BACKGROUND

Porcine urinary bladders are widely used for uro-pharmacological examinations due to their resemblance to the human organ. However, characterisations of the porcine urothelium at the molecular level are scarce up to now. As it has become clear over the last years that this tissue plays an important role in the signaling-pathways of the bladder, we examined whether the transporter and receptor pattern (with focus on the transmitter acetylcholine) is comparable to the human urothelium. With regard to in vitro studies, we also investigated if there is a difference between the native tissue and cultivated primary urothelial cells in culture.

METHODS

Urothelium from German Landrace and Göttingen Minipig bladders was collected. One part of the German Landrace tissue was used for cultivation, and different passages of the urothelial cells were collected. The actual mRNA expression of different transporters and receptors was examined via quantitative real-time PCR. These included the vesicular acetylcholine transporter (VAChT), the choline acetyl transferase (ChAT), organic cation transporters 1-3 (OCT1-3), organic anion transporting polypeptide 1A2 (OATP1A2), P-glycoprotein (ABCB1), the carnitine acetyl-transferase (CarAT), as well as the muscarinic receptors 1-5 (M1-5).

RESULTS

There is a strong qualitative resemblance between the human and the porcine urothelium with regard to the investigated cholinergic receptors, enzymes and transporters. CarAT, OCT1-3, OATP1A2 and ABCB1 could be detected in the urothelium of both pig races. Moreover, all 5 M-receptors were prominent with an emphasis on M2 and M3. VAChT and ChAT could not be detected at all. Cultures of the derived urothelial cells showed decreased expression of all targets apart from ABCB1 and CarAT.

CONCLUSIONS

Based on the expression pattern of receptors, transporters and enzymes of the cholinergic system, the porcine urinary bladder can be regarded as a good model for pharmacological studies. However, cultivation of primary urothelial cells resulted in a significant drop in mRNA expression of the targets. Therefore, it can be concluded that the intact porcine urothelium, or the whole pig bladder, may be appropriate models for studies with anticholinergic drugs, whereas cultivated urothelial cells have some limitation due to significant changes in the expression levels of relevant targets.

Molecular Determinants Conferring the Stoichiometric-Dependent Activity of α-Conotoxins at the Human α9α10 Nicotinic Acetylcholine Receptor Subtype

α9α10 nicotinic acetylcholine receptors (nAChRs) putatively exist at different stoichiometries. We systematically investigated the molecular determinants of α-conotoxins Vc1.1, RgIA#, and PeIA inhibition at hypothetical stoichiometries of the human α9α10 nAChR. Our results suggest that only Vc1.1 exhibits stoichiometric-dependent inhibition at the α9α10 nAChR. The hydrogen bond between N154 of α9 and D11 of Vc1.1 at the α9(+)-α9(-) interface is responsible for the stoichiometric-dependent potency of Vc1.1.

Increased expression of neuregulin 1 in the urothelium of rat bladder with partial bladder outlet obstruction

Background

This study determined whether changes in the expression of neuregulin (NRG) 1, erbB2 tyrosine kinase (ErbB2) and the M2 muscarinic receptor in the urothelium and detrusor muscle of the rat bladder were associated with partial bladder outlet obstruction (PBOO).

Methods

Male Sprague-Dawley rats (body weight 250–300 g) were used and subdivided into control (n = 10) and PBOO groups (n = 20). PBOO was induced for 21 days, and the expression of NRG1, ErbB2 and M2 muscarinic receptor mRNA and protein was evaluated using reverse transcriptase-polymerase chain reaction (RT-PCR) and western blotting, respectively.

Results

In the urothelium of rat bladder samples, protein expression and mRNA expression of NRG1, ErbB2 and M2 muscarinic receptor were significantly increased in the PBOO group compared to the control group (p < 0.05). Only mRNA expression levels of NRG1/ ErbB2 were higher in the detrusor muscle of the PBOO group compared to the control group (p < 0.05).

Conclusions

Our study demonstrated remarkable changes in the expression of NRG1/ErbB2 receptor mRNA and protein in the urothelium and muscle layer. These results suggest that NRG1 overexpression plays some kind of role against the PBOO-induced upregulated muscarinic receptors in detrusor overactivity.

Urothelium update: how the bladder mucosa measures bladder filling

AIM

This review critically evaluates the evidence on mechanoreceptors and pathways in the bladder urothelium that are involved in normal bladder filling signalling.

METHODS

Evidence from in vitro and in vivo studies on (i) signalling pathways like the adenosine triphosphate pathway, cholinergic pathway and nitric oxide and adrenergic pathway, and (ii) different urothelial receptors that are involved in bladder filling signalling like purinergic receptors, sodium channels and TRP channels will be evaluated. Other potential pathways and receptors will also be discussed.

RESULTS

Bladder filling results in continuous changes in bladder wall stretch and exposure to urine. Both barrier and afferent signalling functions in the urothelium are constantly adapting to cope with these dynamics. Current evidence shows that the bladder mucosa hosts essential pathways and receptors that mediate bladder filling signalling. Intracellular calcium ion increase is a dominant factor in this signalling process. However, there is still no complete understanding how interacting receptors and pathways create a bladder filling signal. Currently, there are still novel receptors investigated that could also be participating in bladder filling signalling.

CONCLUSIONS

Normal bladder filling sensation is dependent on multiple interacting mechanoreceptors and signalling pathways. Research efforts need to focus on how these pathways and receptors interact to fully understand normal bladder filling signalling.

Two differentially structured collagen scaffolds for potential urinary bladder augmentation: proof of concept study in a Göttingen minipig model

Background

The repair of urinary bladder tissue is a necessity for tissue loss due to cancer, trauma, or congenital abnormalities. Use of intestinal tissue is still the gold standard in the urological clinic, which leads to new problems and dysfunctions like mucus production, stone formation, and finally malignancies. Therefore, the use of artificial, biologically derived materials is a promising step towards the augmentation of this specialised tissue. The aim of this study was to investigate potential bladder wall repair by two collagen scaffold prototypes, OptiMaix 2D and 3D, naïve and seeded with autologous vesical cells, as potential bladder wall substitute material in a large animal model.

Methods

Six Göttingen minipigs underwent cystoplastic surgery for tissue biopsy and cell isolation followed by implantation of unseeded scaffolds. Six weeks after the first operation, scaffolds seeded with the tissue cultured autologous urothelial and detrusor smooth muscle cells were implanted into the bladder together with additional unseeded scaffolds for comparison. Cystography and bladder ultrasound were performed to demonstrate structural integrity and as leakage test of the implantation sites. Eighteen, 22, and 32 weeks after the first operation, two minipigs respectively were sacrificed and the urinary tract was examined via different (immunohistochemical) staining procedures and the usage of two-photon laser scanning microscopy.

Results

Both collagen scaffold prototypes in vivo had good ingrowth capacity into the bladder wall including a quick lining with urothelial cells. The ingrowth of detrusor muscle tissue, along with the degradation of the scaffolds, could also be observed throughout the study period.

Conclusions

We could show that the investigated collagen scaffolds OptiMaix 2D and 3D are a potential material for bladder wall substitution. The material has good biocompatible properties, shows a good cell growth of autologous cells in vitro, and a good integration into the present bladder tissue in vivo.

Acetylcholinesterase Inhibitors and Drugs Acting on Muscarinic Receptors- Potential Crosstalk of Cholinergic Mechanisms During Pharmacological Treatment

BACKGROUND

Pharmaceuticals with targets in the cholinergic transmission have been used for decades and are still fundamental treatments in many diseases and conditions today. Both the transmission and the effects of the somatomotoric and the parasympathetic nervous systems may be targeted by such treatments. Irrespective of the knowledge that the effects of neuronal signalling in the nervous systems may include a number of different receptor subtypes of both the nicotinic and the muscarinic receptors, this complexity is generally overlooked when assessing the mechanisms of action of pharmaceuticals.

METHODS

We have search of bibliographic databases for peer-reviewed research literature focused on the cholinergic system. Also, we have taken advantage of our expertise in this field to deduce the conclusions of this study.

RESULTS

Presently, the life cycle of acetylcholine, muscarinic receptors and their effects are reviewed in the major organ systems of the body. Neuronal and non-neuronal sources of acetylcholine are elucidated. Examples of pharmaceuticals, in particular cholinesterase inhibitors, affecting these systems are discussed. The review focuses on salivary glands, the respiratory tract and the lower urinary tract, since the complexity of the interplay of different muscarinic receptor subtypes is of significance for physiological, pharmacological and toxicological effects in these organs.

CONCLUSION

Most pharmaceuticals targeting muscarinic receptors are employed at such large doses that no selectivity can be expected. However, some differences in the adverse effect profile of muscarinic antagonists may still be explained by the variation of expression of muscarinic receptor subtypes in different organs. However, a complex pattern of interactions between muscarinic receptor subtypes occurs and needs to be considered when searching for selective pharmaceuticals. In the development of new entities for the treatment of for instance pesticide intoxication, the muscarinic receptor selectivity needs to be considered. Reactivators generally have a muscarinic M2 receptor acting profile. Such a blockade may engrave the situation since it may enlarge the effect of the muscarinic M3 receptor effect. This may explain why respiratory arrest is the major cause for deaths by esterase blocking.

Brain region-specific effects of immobilization stress on cholinesterases in mice

Brain acetylcholinesterase (AChE) variant AChE_R expression increases with acute stress, and this persists for an extended period, although the timing, strain and laterality differences, have not been explored previously. Acute stress transiently increases acetylcholine release, which in turn may increase activity of cholinesterases. Also the AChE gene contains a glucocorticoid response element (GRE), and stress-inducible AChE transcription and activity changes are linked to increased glucocorticoid levels. Corticotropin-releasing hormone knockout (CRH-KO) mice have basal glucocorticoid levels similar to wild type (WT) mice, but much lower levels during stress. Hence we hypothesized that CRH is important for the cholinesterase stress responses, including butyrylcholinesterase (BChE). We used immobilization stress, acute (30 or 120 min) and repeated (120 min daily × 7) in 48 male mice (24 WT and 24 CRH-KO) and determined AChE_R, AChE and BChE mRNA expression and AChE and BChE activities in left and right brain areas (as cholinergic signaling shows laterality). Immobilization decreased BChE mRNA expression (right amygdala, to 0.5, 0.3 and 0.4, × control respectively) and AChE_R mRNA expression (to 0.5, 0.4 and 0.4, × control respectively). AChE mRNA expression increased (1.3, 1.4 and 1.8-fold, respectively) in the left striatum (Str). The AChE activity increased in left Str (after 30 min, 1.2-fold), decreased in right parietal cortex with repeated stress (to 0.5 × control). BChE activity decreased after 30 min in the right CA3 region (to 0.4 × control) but increased (3.8-fold) after 120 min in the left CA3 region. The pattern of changes in CRH-KO differed from that in WT mice.

Overactive bladder in children

Overactive bladder (OAB) is a ubiquitous syndrome that is defined by urinary urgency with, or without urinary incontinence. OAB is observed in all parts of the world, with a prevalence of 5-12% in children (5-10 years of age) and a prevalence of 0.5% in older adolescents (16-18 years of age). Published data indicate that around a third of children with OAB are likely to become adults with similar complaints. Studies in children and in adults with OAB indicate that these individuals are more likely to also have anxiety, depression and attention deficit problems, and that appropriate treatment of these comorbidities can often improve the patient's OAB symptoms. Furthermore, data from twin studies and familial surveys seem to indicate a genetic component of OAB. Pharmacological treatments of OAB in children have improved in the past 5 years, moving beyond anticholinergic agents and including the off-label use of α-blockers, β3-agonists and intravesical botulinum toxin. Use of several different electrical stimulation techniques is also effective, both as first-line treatments, and for patients with treatment-refractory symptoms. Overall the outlook of children with OAB seems to be improving, with a greater understanding of the pathophysiology of this syndrome. Treatment modalities that target the source of the underlying problem, especially in children, are likely to provide the best patient outcomes.

The orphan pentameric ligand-gated ion channel pHCl-2 is gated by pH and regulates fluid secretion in Drosophila Malpighian tubules

Pentameric ligand-gated ion channels (pLGICs) constitute a large protein superfamily in metazoa whose role as neurotransmitter receptors mediating rapid, ionotropic synaptic transmission has been extensively studied. Although the vast majority of pLGICs appear to be neurotransmitter receptors, the identification of pLGICs in non-neuronal tissues and homologous pLGIC-like proteins in prokaryotes points to biological functions, possibly ancestral, that are independent of neuronal signalling. Here, we report the molecular and physiological characterization of a highly divergent, orphan pLGIC subunit encoded by the pHCl-2 (CG11340) gene, in Drosophila melanogaster We show that pHCl-2 forms a channel that is insensitive to a wide array of neurotransmitters, but is instead gated by changes in extracellular pH. pHCl-2 is expressed in the Malpighian tubules, which are non-innervated renal-type secretory tissues. We demonstrate that pHCl-2 is localized to the apical membrane of the epithelial principal cells of the tubules and that loss of pHCl-2 reduces urine production during diuresis. Our data implicate pHCl-2 as an important source of chloride conductance required for proper urine production, highlighting a novel role for pLGICs in epithelial tissues regulating fluid secretion and osmotic homeostasis.

Phosphocholine - an agonist of metabotropic but not of ionotropic functions of α9-containing nicotinic acetylcholine receptors

We demonstrated previously that phosphocholine and phosphocholine-modified macromolecules efficiently inhibit ATP-dependent release of interleukin-1β from human and murine monocytes by a mechanism involving nicotinic acetylcholine receptors (nAChR). Interleukin-1β is a potent pro-inflammatory cytokine of innate immunity that plays pivotal roles in host defence. Control of interleukin-1β release is vital as excessively high systemic levels cause life threatening inflammatory diseases. In spite of its structural similarity to acetylcholine, there are no other reports on interactions of phosphocholine with nAChR. In this study, we demonstrate that phosphocholine inhibits ion-channel function of ATP receptor P2X7 in monocytic cells via nAChR containing α9 and α10 subunits. In stark contrast to choline, phosphocholine does not evoke ion current responses in Xenopus laevis oocytes, which heterologously express functional homomeric nAChR composed of α9 subunits or heteromeric receptors containing α9 and α10 subunits. Preincubation of these oocytes with phosphocholine, however, attenuated choline-induced ion current changes, suggesting that phosphocholine may act as a silent agonist. We conclude that phophocholine activates immuno-modulatory nAChR expressed by monocytes but does not stimulate canonical ionotropic receptor functions.

Anti-hypersensitive effect of intramuscular administration of αO-conotoxin GeXIVA[1,2] and GeXIVA[1,4] in rats of neuropathic pain

αO-conotoxin GeXIVA (GeXIVA) is a potent antagonist of α9α10 nicotinic acetylcholine receptors (nAChRs), which has four Cys residues and three disulfide isomers. Among the 3 isomers, both GeXIVA[1,2] (bead isomer) and GeXIVA[1,4] (ribbon isomer) showed potent block on α9α10 nAChRs with close low nanomolar IC50s. Here we report that anti-hypersensitive effects of the bead and ribbon isomers in the chronic constriction injury (CCI) model of neuropathic pain and acute pain model of tail flick test. Treatment was started and continued for 7 or 14days after the development of hyperalgesia which was induced by CCI surgery. GeXIVA[1,2] and GeXIVA[1,4] significantly reduced mechanical allodynia in CCI rats without tolerance, in which GeXIVA[1,2] remained up to two weeks after intramuscular administration of the toxins was ceased. The pain reliever effect of GeXIVA[1,2] on neuropathic rats was slightly better than GeXIVA[1,4]. The two isomers did not suppress the acute thermal pain behaviors significantly when they were tested in the tail flick model by intramuscular bolus injection. Both GeXIVA[1,2] and GeXIVA[1,4] had no significant effect on performance of rats in the accelerating rotarod test after intramuscular injections. This suggests that αO-conotoxin GeXIVA[1,2] and GeXIVA[1,4] may offer new strategies to the treatment of neuropathic pain.

Expression of brain derived-neurotrophic factor and granulocyte-colony stimulating factor in the urothelium: relation with voiding function

BACKGROUND

We designed this experiment to elucidate the relationship between the expression of brain derived-neurotrophic factor (BDNF), the expression of granulocyte-colony stimulating factor (G-CSF), and the development of overactive bladder (OAB). In our previous study, the urothelium was observed to be more than a simple mechanosensory receptor and was found to be a potential therapeutic target for OAB. Moreover, neuregulin-1 and BDNF were found to be potential new biomarkers of OAB. Here, we investigated the relationship between changes in the voiding pattern and the expression of BDNF and G-CSF in the urothelium and evaluated the effects of 5-hydroxymethyl tolterodine (5-HMT) on rats with bladder outlet obstruction (BOO).

METHODS

A total of 100 Sprague-Dawley rats were divided into the following groups: 20 control rats; 40 BOO rats; and 40 BOO rats administered 5-HMT (0.1 mg/kg). After BOO was induced for 4 weeks, the rats were assessed by cystometrography. The changes in BDNF and G-CSF expression were examined in both separated urothelial tissues and in cultured urothelial cells by reverse transcription polymerase chain reaction (RT-PCR).

RESULTS

BOO rats showed increased non-voiding activity [NVA; (number/10 voidings)] and bladder weight and decreased micturition volume (MV), micturition interval (MI), and micturition time (MT) relative to the controls. Moreover, the 5-HMT administration rats showed decreased NVA and bladder weight and increased MV and MI in comparison to the BOO rats. BDNF and G-CSF expression was increased in BOO rats and decreased following 5-HMT administration. In this model, voiding dysfunction developed as a result of BOO. As a therapeutic agent for OAB, the administration of 5-HMT improved the voiding dysfunction.

CONCLUSIONS

BDNF and G-CSF might modulate voiding patterns through micturition pathways and might be involved only in the urothelium. Moreover, the expression of both genes in the urothelium might be related to voiding dysfunction in OAB patients. Thus, the urothelium has an important role in the manifestation of voiding symptoms.

Role of Nicotinic Acetylcholine Receptor α3 and α7 Subunits in Detrusor Overactivity Induced by Partial Bladder Outlet Obstruction in Rats

Purpose:

To investigate the role of α3 and α7 nicotinic acetylcholine receptor subunits (nAChRs) in the bladder, using a rat model with detrusor overactivity induced by partial bladder outlet obstruction (BOO).

Methods:

Forty Sprague-Dawley rats were used: 10 were sham-operated (control group) and 30 were observed for 3 weeks after partial BOO. BOO-induced rats were further divided into 3 groups: Two groups of 10 rats each received intravesicular infusions with hexamethonium (HM group; n=10) or methyllycaconitine (MLC group; n=10), which are antagonists for α3 and α7 nAChRs, respectively. The remaining BOO-induced rats received only saline infusion (BOO group; n=10). Based on the contraction interval measurements using cystometrogram, the contraction pressure and nonvoiding bladder contractions were compared between the control and the three BOO-induced groups. Immunofluorescent staining and Western blotting were used to analyze α3 and α7 nAChRs levels.

Results:

The contraction interval of the MLC group was higher than that of the BOO group (P<0.05). Nonvoiding bladder contraction almost disappeared in the HM and MLC groups. Contraction pressure increased in the BOO group (P<0.05) compared with the control group and decreased in the HM and MLC groups compared with the BOO group (P<0.05). Immunofluorescence staining showed that the α3 nAChR signals increased in the urothelium, and the α7 nAChR signals increased in the urothelium and detrusor muscle of the BOO group compared with the control group. Western blot analysis showed that both α3 and α7 nAChR levels increased in the BOO group (P<0.05).

Conclusions:

Alpha3 and α7 nAChRs are associated with detrusor overactivity induced by BOO. Furthermore, nAChR antagonists could help in clinically improving detrusor overactivity.

Laser-capture microdissection for analysis of cell type-specific gene expression of muscarinic receptor subtypes in the rat bladder with cyclophosphamide-induced cystitis

PURPOSE

This study examined whether the laser-capture microdissection (LCM) method can achieve separation of urothelial cells from detrusor cells or superficial urothelial cells from intermediate/basal urothelial cells, using α-smooth muscle actin (SMA) and cytokeratin 20 (CK20). In addition, we investigated the changes in expression of muscarinic receptors in laser-captured urothelial and detrusor cells in rats with chronic cystitis.

METHODS

Female SD rats were injected with cyclophosphamide (75 mg/kg) intraperitoneally at day 1, 4, 7 and 10 to induce chronic cystitis. Saline was injected in the same protocol for controls. Bladder specimens were cut at 8 μm thickness, fixed in 70% ethanol and lightly stained by hematoxylin and eosin, and then superficial urothelium, intermediate/basal urothelium and detrusor muscles were laser-captured separately. Real-time PCR was performed to examine expressions of α-SMA, CK20, muscarinic 2 receptors (M2R) and muscarinic 3 receptors (M3R).

RESULTS

The expression of α-SMA mRNA in detrusor muscle cells was 200 times higher than that in urothelial cells in controls. CK20 mRNA expression in apical urothelial cells was 55 times more than that in detrusor muscle and four times more than that in intermediate/basal urothelial cells. Expressions of M2R and M3R mRNA were increased in urothelial cells and decreased in detrusor muscles following chronic cystitis.

CONCLUSIONS

The LCM could be useful for tissue collection of detrusor muscle and different layers of urothelial cells with minimal contamination of other cell types, and cell type-specific changes in molecular expression could accurately be analyzed. Increased expression of urothelial MR might enhance urothelial-afferent interactions to induce bladder overactivity/pain conditions associated with bladder inflammation.

Therapeutic modulation of urinary bladder function: multiple targets at multiple levels

Storage dysfunction of the urinary bladder, specifically overactive bladder syndrome, is a condition that occurs frequently in the general population. Historically, pathophysiological and treatment concepts related to overactive bladder have focused on smooth muscle cells. Although these are the central effector, numerous anatomic structures are involved in their regulation, including the urothelium, afferent and efferent nerves, and the central nervous system. Each of these structures involves receptors for—and the urothelium itself also releases—many mediators. Moreover, hypoperfusion, hypertrophy, and fibrosis can affect bladder function. Established treatments such as muscarinic antagonists, β-adrenoceptor agonists, and onabotulinumtoxinA each work in part through their effects on the urothelium and afferent nerves, as do α1-adrenoceptor antagonists in the treatment of voiding dysfunction associated with benign prostatic hyperplasia; however, none of these treatments are specifically targeted to the urothelium and afferent nerves. It remains to be explored whether future treatments that specifically act at one of these structures will provide a therapeutic advantage.

Signalling molecules in the urothelium

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

Purinergic and muscarinic modulation of ATP release from the urothelium and its paracrine actions

The urothelium is a newly recognized sensory structure that detects bladder fullness. Pivotal to this sensory role is the release of ATP from the urothelium. However, the routes for urothelial ATP release, its modulation by receptor-mediated pathways, and the autocrine/paracrine role of ATP are poorly understood, especially in native tissue. We examined the action of key neurotransmitters: purinergic and muscarinic agonists on ATP release and its paracrine effect. Guinea pig and human urothelial mucosa were mounted in a perfusion trough; superfusate ATP was measured using a luciferin-luciferase assay, and tissue contractions were recorded with a tension transducer. Intracellular Ca²⁺ was measured in isolated urothelial cells with fura-2. The P2Y agonist UTP but not the P2X agonist α,β-methylene-ATP generated ATP release. The muscarinic agonist carbachol and the M₂-preferential agonist oxotremorine also generated ATP release, which was antagonized by the M₂-specific agent methoctramine. Agonist-evoked ATP release was accompanied by mucosal contractions. Urothelial ATP release was differentially mediated by intracellular Ca²⁺ release, cAMP, exocytosis, or connexins. Urothelium-attached smooth muscle exhibited spontaneous contractions that were augmented by subthreshold concentrations of carbachol, which had little direct effect on smooth muscle. This activity was attenuated by desensitizing P2X receptors on smooth muscle. Urothelial ATP release was increased in aging bladders. Purinergic and muscarinic agents produced similar effects in human urothelial tissue. This is the first demonstration of specific modulation of urothelial ATP release in native tissue by purinergic and muscarinic neurotransmitters via distinct mechanisms. Released ATP produces paracrine effects on underlying tissues. This process is altered during aging and has relevance to human bladder pathologies.

Orally administered nicotine induces urothelial hyperplasia in rats and mice

Tobacco smoking is a major risk factor for multiple human cancers including urinary bladder carcinoma. Tobacco smoke is a complex mixture containing chemicals that are known carcinogens in humans and/or animals. Aromatic amines a major class of DNA-reactive carcinogens in cigarette smoke, are not present at sufficiently high levels to fully explain the incidence of bladder cancer in cigarette smokers. Other agents in tobacco smoke could be excreted in urine and enhance the carcinogenic process by increasing urothelial cell proliferation. Nicotine is one such major component, as it has been shown to induce cell proliferation in multiple cell types in vitro. However, in vivo evidence specifically for the urothelium is lacking. We previously showed that cigarette smoke induces increased urothelial cell proliferation in mice. In the present study, urothelial proliferative and cytotoxic effects were examined after nicotine treatment in mice and rats. Nicotine hydrogen tartrate was administered in drinking water to rats (52 ppm nicotine) and mice (514 ppm nicotine) for 4 weeks and urothelial changes were evaluated. Histopathologically, 7/10 rats and 4/10 mice showed simple hyperplasia following nicotine treatment compared to none in the controls. Rats had an increased mean BrdU labeling index compared to controls, although it was not statistically significantly elevated in either species. Scanning electron microscopic visualization of the urothelium did not reveal significant cytotoxicity. These findings suggest that oral nicotine administration induced urothelial hyperplasia (increased cell proliferation), possibly due to a mitogenic effect of nicotine and/or its metabolites.

Urothelial signaling

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

Regulation of glutamate release by heteromeric nicotinic receptors in layer V of the secondary motor region (Fr2) in the dorsomedial shoulder of prefrontal cortex in mouse

We studied how nicotinic acetylcholine receptors (nAChRs) regulate glutamate release in the secondary motor area (Fr2) of the dorsomedial murine prefrontal cortex, in the presence of steady agonist levels. Fr2 mediates response to behavioral situations that require immediate attention and is a candidate for generating seizures in the frontal epilepsies caused by mutant nAChRs. Morphological analysis showed a peculiar chemoarchitecture and laminar distribution of pyramidal cells and interneurons. Tonic application of 5 µM nicotine on Layer V pyramidal neurons strongly increased the frequency of spontaneous glutamatergic excitatory postsynaptic currents. The effect was inhibited by 1 µM dihydro-β-erythroidine (which blocks α4-containing nAChRs) but not by 10 nM methyllicaconitine (which blocks α7-containing receptors). Excitatory postsynaptic currents s were also stimulated by 5-iodo-3-[2(S)-azetidinylmethoxy]pyridine, selective for β2-containing receptors, in a dihydro-β-erythroidine -sensitive way. We next studied the association of α4 with different populations of glutamatergic terminals, by using as markers the vesicular glutamate transporter type (VGLUT) 1 for corticocortical synapses and VGLUT2 for thalamocortical projecting fibers. Immunoblots showed higher expression of α4 in Fr2, as compared with the somatosensory cortex. Immunofluorescence showed intense VGLUT1 staining throughout the cortical layers, whereas VGLUT2 immunoreactivity displayed a more distinct laminar distribution. In Layer V, colocalization of α4 nAChR subunit with both VGLUT1 and VGLUT2 was considerably stronger in Fr2 than in somatosensory cortex. Thus, in Fr2, α4β2 nAChRs are expressed in both intrinsic and extrinsic glutamatergic terminals and give a major contribution to control glutamate release in Layer V, in the presence of tonic agonist levels.

Alteration in TRPV1 and Muscarinic (M3) receptor expression and function in idiopathic overactive bladder urothelial cells

AIM

To examine function of both cholinergic (muscarinic) and TRPV1 receptors in human bladder urothelial (HBUC) from non-neurogenic overactive bladder (OAB) patients as compared to control subjects.

METHODS

Primary HBUC cultures were derived from cystoscopic biopsies from OAB and control subjects. Muscarinic and TRPV1 function was assessed by acetylcholine (5 μm) or capsaicin (0.5 μm) evoked ATP release, measured by luciferase assay. Overall, expression of TRPV1 and muscarinic M3 receptors in bladder urothelial cells was accomplished using western immunoblotting.

RESULTS

Our findings revealed that the response to acetylcholine in OAB HBUC cultures (which was blocked by the nonselective muscarinic antagonist, atropine methyl nitrate or AMN) was not significantly different than from controls. The acetylcholine M3 receptor was slightly decreased as compared to control. In contrast, OAB HBUC cultures exhibited a capsaicin hypersensitivity and augmented release of ATP (3.2 fold higher), which was blocked by the antagonist capsazepine. The increase in capsaicin sensitivity correlated with increased urothelial TRPV1 expression.

CONCLUSION

Though characterized in a small number of subjects, augmented release of urothelial-derived transmitters such as ATP could 'amplify' signalling between and within urothelial cells and nearby afferent nerves.

Latest treatment for lower urinary tract dysfunction: therapeutic agents and mechanism of action

Recent studies suggest that antimuscarinics might suppress bladder afferent activity by blocking muscarinic receptors in the urothelium, myofibroblasts and detrusor, thereby improving overactive bladder symptoms. β(3)-Adrenoceptors are predominantly expressed in the human bladder and mediate relaxation of detrusor muscle. β(3)-Adrenoceptor agonists increase bladder capacity and prolong micturition interval. It is assumed that β(3)-adrenoceptor agonists could exert an inhibitory effect on bladder afferent through β(3)-adrenoceptors in the urothelium and detrusor, which eventually improve the symptom of urgency. Mirabegron is a potent and selective β(3)-adrenoceptor agonist. A Japanese phase 3 study showed that mirabegron has excellent efficacy and safety for treating overactive bladder. α(1)-Adrenoceptor antagonists (α(1)-blockers) have become a mainstay of male lower urinary tract symptoms treatment. The α(1)(A) subtype is known to mediate functional obstruction as a result of benign prostatic enlargement. Recent studies have suggested that α(1)(A)-adrenoceptors are additionally involved in the generation of storage symptoms. The α(1)(D) subtype is thought to play a role in the facilitation of voiding reflex; that is; storage symptoms. α(1)-Blockers often fail to alleviate overactive bladder symptoms. In this context, combination therapy with α(1)-blockers and antimuscarinics has been recommended. Treatment with 5α-reductase inhibitor for 1 year improves urinary symptoms and flow rate by reducing prostatic volume in men with benign prostatic enlargement. A pooled analysis showed that the long-term (2 or 4 years) treatment with 5α-reductase inhibitor reduced the rate of progression to acute urinary retention and surgery. Combination therapy with 5α-reductase inhibitor and α(1)-blocker was shown to provide a rapid improvement in lower urinary tract symptoms, and reduce the relative risk of acute urinary retention and benign prostatic hyperplasia-related surgery. Phosphodiesterase inhibitors might target a nitric oxide-cyclic guanosine monophosphate pathway in the prostate, urethra and bladder. Phosphodiesterase-5 inhibitors (sildenafil or tadalafil) were shown to provide clinically relevant improvements in both male lower urinary tract symptoms and erectile dysfunction.

The regulation of distention-induced ATP release from urothelium by the adenylyl cyclase-cyclic AMP pathway

Distention of the bladder during urine storage induces ATP release from urothelium, thereby facilitating transmission of visceral sensory signals to afferent nerve fibers. An excess of urothelial ATP release was found in interstitial cystitis, a condition accompanied by hyperesthesia of the urinary bladder; it remains unclear which signals are involved in this upregulation. The present study demonstrated that the adenylyl cyclase pathway enhances distention-induced ATP release in mouse bladder. In the absence of distention, adenylyl cyclase activation by forskolin or cyclic AMP increases by rolipram did not induce significant ATP release. However, forskolin or rolipram significantly enhanced ATP release from urothelium by a physiologically normal urine storage pressure (5 cmH(2)O). Blockade of adenylyl cyclases did not alter pressure-induced ATP release in normal condition. Thus, the adenylyl cyclase-cAMP pathway might be activated in pathological conditions and cause an excess of ATP release.

Luminal cholinergic signalling in airway lining fluid: a novel mechanism for activating chloride secretion via Ca²⁺-dependent Cl⁻ and K⁺ channels

BACKGROUND AND PURPOSE

Recent studies detected the expression of proteins involved in cholinergic metabolism in airway epithelial cells, although the function of this non-neuronal cholinergic system is not known in detail. Thus, this study focused on the effect of luminal ACh as a regulator of transepithelial ion transport in epithelial cells.

EXPERIMENTAL APPROACH

RT-PCR experiments were performed using mouse tracheal epithelial cells for ChAT and organic cation transporter (OCT) transcripts. Components of tracheal airway lining fluid were analysed with desorption electrospray ionization (DESI) MS. Effects of nicotine on mouse tracheal epithelial ion transport were examined with Ussing-chamber experiments.

KEY RESULTS

Transcripts encoding ChAT and OCT1-3 were detected in mouse tracheal epithelial cells. The DESI experiments identified ACh in the airway lining fluid. Luminal ACh induced an immediate, dose-dependent increase in the transepithelial ion current (EC₅₀: 23.3 µM), characterized by a transient peak and sustained plateau current. This response was not affected by the Na⁺-channel inhibitor amiloride. The Cl⁻-channel inhibitor niflumic acid or the K⁺-channel blocker Ba²⁺ attenuated the ACh effect. The calcium ionophore A23187 mimicked the ACh effect. Luminal nicotine or muscarine increased the ion current. Experiments with receptor gene-deficient animals revealed the participation of muscarinic receptor subtypes M₁ and M₃.

CONCLUSIONS AND IMPLICATIONS

The presence of luminal ACh and activation of transepithelial ion currents by luminal ACh receptors identifies a novel non-neuronal cholinergic pathway in the airway lining fluid. This pathway could represent a novel drug target in the airways.

Alterations in the non-neuronal acetylcholine synthesis and release machinery in esophageal epithelium

AIMS

A non-neuronal cholinergic system has been described in epithelial cells including that of the urinary bladder (urothelium) and the upper gastrointestinal tract (esophagus). Epithelial dysfunction has been implicated in the pathophysiology of persistent pain conditions such as painful bladder syndrome as well as functional heartburn. For example, alterations in the ability to synthesize and release acetylcholine may contribute to changes in epithelial sensory and barrier function associated with a number of functional genitourinary and intestinal disorders.

MAIN METHODS

We examined using immunoblot, acetylcholine (ACh)-synthesis and release components in cat esophageal mucosa and whether elements of these components are altered in a naturally occurring model of chronic idiopathic cystitis termed feline interstitial cystitis (FIC).

KEY FINDINGS

We identified proteins involved in ACh synthesis and release (high affinity choline transporter, CHT1; ACh synthesizing enzyme choline acetyltransferase ChAT and carnitine acetyltransferase CarAT; vesicular ACh transporter VAChT and the organic cation transporter isoforms 1-3 or OCT-1-3) in cat esophageal mucosa. Significant alterations in CHT, ChAT, VAChT and OCT-1 were detected in the esophageal mucosa from FIC cats. Changes in the vesicular nucleotide transporter (VNUT) and the junctional protein pan-cadherin were also noted.

SIGNIFICANCE

Taken together, these findings suggest that changes in the non-neuronal cholinergic system may contribute to alterations in cell-cell contacts and possibly communication with underlying cells that may contribute to changes in sensory function and visceral hyperalgesia in functional esophageal pain.

Muscarinic agonists and antagonists: effects on the urinary bladder

Voiding of the bladder is the result of a parasympathetic muscarinic receptor activation of the detrusor smooth muscle. However, the maintenance of continence and a normal bladder micturition cycle involves a complex interaction of cholinergic, adrenergic, nitrergic and peptidergic systems that is currently little understood. The cholinergic component of bladder control involves two systems, acetylcholine (ACh) released from parasympathetic nerves and ACh from non-neuronal cells within the urothelium. The actions of ACh on the bladder depend on the presence of muscarinic receptors that are located on the detrusor smooth muscle, where they cause direct (M₃) and indirect (M₂) contraction; pre-junctional nerve terminals where they increase (M₁) or decrease (M₄) the release of ACh and noradrenaline (NA); sensory nerves where they influence afferent nerve activity; umbrella cells in the urothelium where they stimulate the release of ATP and NO; suburothelial interstitial cells with unknown function; and finally, other unidentified sites in the urothelium from where prostaglandins and inhibitory/relaxatory factors are released. Thus, the actions of muscarinic receptor agonists and antagonists on the bladder may be very complex even when considering only local muscarinic actions. Clinically, muscarinic antagonists remain the mainstay of treatment for the overactive bladder (OAB), while muscarinic agonists have been used to treat hypoactive bladder. The antagonists are effective in treating OAB, but their precise mechanisms and sites of action (detrusor, urothelium, and nerves) have yet to be established. Potentially more selective agents may be developed when the cholinergic systems within the bladder are more fully understood.

Activation of nicotinic receptors can contribute to endothelium-dependent relaxations to acetylcholine in the rat aorta

Acetylcholine causes endothelium-dependent relaxations in the rat aorta. Both muscarinic acetylcholine receptors (mAChRs) and nicotinic acetylcholine receptors (nAChRs) are expressed in endothelial cells. It is generally accepted that mAChRs are responsible for the endothelium-dependent relaxations evoked by acetylcholine. The present study was designed to investigate whether nAChRs can also be involved in such responses evoked by the cholinergic transmitter. Rings with or without endothelium of aortae of spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) normotensive rats were suspended in organ chambers for the measurement of isometric tension. In WKY aortae the muscarinic antagonist atropine abolished the relaxations to increasing concentrations of acetylcholine, confirming that mAChRs are responsible mainly for the response under control conditions. In SHR aortae, atropine caused only partial inhibition of the endothelium-dependent relaxations to acetylcholine; the remaining decreases in tension were inhibited by the nicotinic antagonist mecamylamine, which did not significantly affect the response in the absence of atropine in either SHR or WKY preparations. Thus, when mAChRs are inhibited, nAChRs mediate relaxation to the cholinergic transmitter in the SHR but not the WKY aorta. Nicotine, a direct agonist of the nicotinic receptor, induced endothelium-dependent relaxations in both SHR and WKY rats via the activation of α7-nAChRs, but not by mecamylamine-sensitive nicotinic receptors (α3 subtype). The acetylcholine-induced, atropine-insensitive relaxations and those to nicotine both involve the phosphatidylinositol 3-kinase/AKT pathway. The present study demonstrates that the activation of nAChRs can contribute to acetylcholine-induced, endothelium-dependent relaxations in the aortae of hypertensive animals and suggests that these receptors may contribute to the endothelium-dependent regulation of vascular tone.

Differential expression and function of nicotinic acetylcholine receptors in the urinary bladder epithelium of the rat

It has been previously determined that the epithelial lining of the urinary bladder, or urothelium, expresses two subtypes of nicotinic acetylcholine receptors (nAChRs) that mediate distinct physiological effects in vivo. These effects include inhibition of bladder reflexes through α7 receptors and an excitation of bladder reflexes through α3-containing (α3*) receptors. It is believed that urothelial receptors mediate their effects through modulating the release of neurotransmitters such as ATP that subsequently influence bladder afferent nerve excitability. Therefore, we examined the distribution of nAChRs in the urothelium, as well as their ability to influence the release of the neurotransmitter ATP. Immunofluorescent staining of both whole bladder tissue and primary urothelial cultures from the rat demonstrated that the urothelium contains both α3* and α7 receptors. In primary urothelial cultures, α7 stimulation with choline (10 μM to 1 mM) caused a decrease in basal ATP release while α3* stimulation with cytisine (1–100 μM) caused a concentration-dependent, biphasic response, with low concentrations (1–10 μM) inhibiting release and higher concentrations (50–100 μM) increasing release. These responses were mirrored in an in vitro, whole bladder preparation. In vivo, excitation of bladder reflexes in response to intravesical cytisine (100 μM) is blocked by systemic administration of the purinergic antagonist PPADS (1 or 3 μg kg(−1)). We also examined how each receptor subtype influenced intracellular Ca2+ levels in cultured urothelial cells. nAChR stimulation increased [Ca2+]i through distinct mechanisms: α7 through a ryanodine-sensitive intracellular mechanism and α3* through extracellular influx. In addition, our findings suggest interactions between nAChR subtypes whereby activation of α7 receptors inhibited the response to a subsequent activation of α3* receptors, preventing the increase in [Ca2+]i previously observed. This inhibitory effect appears to be mediated through protein kinase A- or protein kinase C-mediated pathways.

Activation of muscarinic receptors by non-neuronal acetylcholine

The biological role of acetylcholine and the cholinergic system is revisited based particularly on scientific research early and late in the last century. On the one hand, acetylcholine represents the classical neurotransmitter, whereas on the other hand, acetylcholine and the pivotal components of the cholinergic system (high-affinity choline uptake, choline acetyltransferase and its end product acetylcholine, muscarinic and nicotinic receptors and esterase) are expressed by more or less all mammalian cells, i.e. by the majority of cells not innervated by neurons at all. Moreover, it has been demonstrated that acetylcholine and "cholinergic receptors" are expressed in non-neuronal organisms such as plants and protists. Acetylcholine is even synthesized by bacteria and algae representing an extremely old signalling molecule on the evolutionary timescale. The following article summarizes examples, in which non-neuronal acetylcholine is released from primitive organisms as well as from mammalian non-neuronal cells and binds to muscarinic receptors to modulate/regulate phenotypic cell functions via auto-/paracrine pathways. The examples demonstrate that non-neuronal acetylcholine and the non-neuronal cholinergic system are vital for various types of cells such as epithelial, endothelial and immune cells.

Muscarinic Acetylcholine Receptor M3 Mutation Causes Urinary Bladder Disease and a Prune-Belly-like Syndrome

Urinary bladder malformations associated with bladder outlet obstruction are a frequent cause of progressive renal failure in children. We here describe a muscarinic acetylcholine receptor M3 (CHRM3) (1q41-q44) homozygous frameshift mutation in familial congenital bladder malformation associated with a prune-belly-like syndrome, defining an isolated gene defect underlying this sometimes devastating disease. CHRM3 encodes the M3 muscarinic acetylcholine receptor, which we show is present in developing renal epithelia and bladder muscle. These observations may imply that M3 has a role beyond its known contribution to detrusor contractions. This Mendelian disease caused by a muscarinic acetylcholine receptor mutation strikingly phenocopies Chrm3 null mutant mice.

Researching bladder afferents-determining the effects of β(3) -adrenergic receptor agonists and botulinum toxin type-A

A substantial portion of the current research on lower urinary tract dysfunction is focused on afferent mechanisms. The main goals are to define and modulate the signaling pathways by which afferent information is generated, enhanced and conveyed to the central nervous system. Alterations in bladder afferent mechanisms are a potential source of voiding dysfunction and an emerging source for drug targets. Established drug therapies such as muscarinic receptor antagonists, and two emerging therapies, β(3) -adrenergic receptor agonists and botulinum toxin type-A, may act partly through afferent mechanisms. This review focuses on these two new principles and new and established methods for determining their sites of action. It also provides brief information on the innervation of the bladder, afferent receptors and transmitters and how these may communicate with the urothelium, interstitial cells and detrusor smooth muscle to regulate micturition. Peripheral and central mechanisms of afferent sensitization and myogenic mechanisms that lead to detrusor overactivity, overactive bladder symptoms and urgency sensations are also covered. This work is the result from 'Think Tank' presentations, and the lengthy discussions that followed, at the 2010 International Consultation on Incontinence Research Society meeting in Bristol, UK.

Urothelial signaling

The urinary bladder "mucosa" or innermost portion of the bladder is composed of transitional epithelium, basement membrane, and the lamina propria. This chapter reviews the specialized anatomy of the bladder epithelium (urothelium) and speculates on possible communication mechanisms from urothelial cells to various cell types within the bladder wall. For example, beyond serving as a simple barrier, there is growing evidence that the urinary bladder urothelium exhibits specialized sensory properties and plays a key role in the detection and transmission of both physiological and nociceptive stimuli. Findings from a number of studies suggest that the urothelium exhibits both "sensor" (expressing receptors/ion channels capable of responding to thermal, mechanical, and chemical stimuli) and "transducer" (ability to release chemicals) properties. Thus, 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.

Afferent mechanism in the urinary tract

Much of the current research on lower urinary tract dysfunction is focused on afferent mechanisms. The main goals are to define and modulate the signaling pathways by which afferent information is generated and conveyed to the central nervous system. Alterations in bladder afferent mechanisms are a potential source of voiding dysfunction and an emerging source of drug targets. Even some established drug therapies such as muscarinic receptor antagonists, as well as emerging therapies such as botulinum toxin type-A, may act partly through afferent mechanisms. This review presents up-to-date findings on the localization of afferent fiber types within the bladder wall, afferent receptors and transmitters, and how these may communicate with the urothelium, interstitial cells, and detrusor smooth muscle to regulate micturition in normal and pathological bladders. Peripheral and central mechanisms of afferent sensitization and myogenic mechanisms that lead to detrusor overactivity, overactive bladder symptoms, and urgency sensations are also covered as well as new therapeutic approaches and new and established methods of measuring afferent activity.

Non-neuronal regulation and repertoire of cholinergic receptors in organs

Many studies on the cholinergic pathway have indicated that cholinergic receptors, which are widely expressed in various cells, play an important role in all body organs. In this review, we present the concept that cholinergic responses are regulated through a neuronal or non-neuronal mechanism. The neuronal mechanism is a system in which acetylcholine binds to cholinergic receptors on target cells through the nerves. In the non-neuronal mechanism, acetylcholine, produced by neighboring cells in an autocrine/paracrine manner, binds to cholinergic receptors on target cells. Both mechanisms subsequently lead to physiological and pathophysiological responses. We also investigated the subunits/subtypes of cholinergic receptors on target cells, physiological and pathophysiological responses of the organs via cholinergic receptors, and extracellular factors that alter the subtypes/subunits of cholinergic receptors. Collectively, this concept will elucidate how cholinergic responses occur and will help us conduct further experiments to develop new therapeutic agents.

Is the urothelium intelligent?

The urothelium separates the urinary tract lumen from underlying tissues of the tract wall. Previously considered as merely an effective barrier between these two compartments it is now recognized as a more active tissue that senses and transduces information about physical and chemical conditions within the urinary tract, such as luminal pressure, urine composition, etc. To understand this sensory function it is useful to consider the urothelium and suburothelium as a functional unit; containing uroepithelial cells, afferent and efferent nerve fibers and suburothelial interstitial cells. This structure responds to alterations in its external environment through the release of diffusible agents, such as ATP and acetylcholine, and eventually modulates the activity of afferent nerves and underlying smooth muscles. This review considers different stresses the urothelium/suburothelium responds to; the particular chemicals released; the cellular receptors that are consequently affected; and how nerve and muscle function is modulated. Brief consideration is also to regional differences in the urothelium/suburothelium along the urinary tract. The importance of different pathways in relaying sensory information in the normal urinary tract, or whether they are significant only in pathological conditions is also discussed. An operational definition of intelligence is used, whereby a system (urothelium/suburothelium) responds to external changes, to maximize the possibility of the urinary tract achieving its normal function. If so, the urothelium can be regarded as intelligent. The advantage of this approach is that input-output functions can be mathematically formulated, and the importance of different components contributing to abnormal urinary tract function can be calculated.

Beyond neurons: Involvement of urothelial and glial cells in bladder function

AIM

The urothelium, or epithelial lining of the lower urinary tract (LUT), is likely to play an important role in bladder function by actively communicating with bladder nerves, smooth muscle, and cells of the immune and inflammatory systems. Recent evidence supports the importance of non-neuronal cells that may extend to both the peripheral and central processes of the neurons that transmit normal and nociceptive signals from the urinary bladder. Using cats diagnosed with a naturally occurring syndrome termed feline interstitial cystitis (FIC), we investigated whether changes in physiologic parameters occur within 3 cell types associated with sensory transduction in the urinary bladder: 1) the urothelium, 2) identified bladder dorsal root ganglion (DRG) neurons and 3) grey matter astrocytes in the lumbosacral (S1) spinal cord. As estrogen fluctuations may modulate the severity of many chronic pelvic pain syndromes, we also examined whether 17beta-estradiol (E2) alters cell signaling in rat urothelial cells.

RESULTS

We have identified an increase in nerve growth factor (NGF) and substance P (SP) in urothelium from FIC cats over that seen in urothelium from unaffected (control) bladders. The elevated NGF expression by FIC urothelium is a possible cause for the increased cell body size of DRG neurons from cats with FIC, reported in this study. At the level of the spinal cord, astrocytic GFAP immuno-intensity was significantly elevated and there was evidence for co-expression of the primitive intermediate filament, nestin (both indicative of a reactive state) in regions of the FIC S1 cord (superficial and deep dorsal horn, central canal and laminae V-VIl) that receive input from pelvic afferents. Finally, we find that E2 triggers an estrus-modifiable activation of p38 MAPK in rat urothelial cells. There were cyclic variations with E2-mediated elevation of p38 MAPK at both diestrus and estrus, and inhibition of p38 MAPK in proestrous urothelial cells.

CONCLUSION

Though urothelial cells are often viewed as bystanders in the processing of visceral sensation, these and other findings support the view that these cells function as primary transducers of some physical and chemical stimuli. In addition, the pronounced activation of spinal cord astrocytes in an animal model for bladder pain syndrome (BPS) may play an important role in the pain syndrome and open up new potential approaches for drug intervention.

Antimuscarinics and overactive bladder: other mechanism of action

Antimuscarinics are considered first-line treatment for patients with overactive bladder (OAB). However, the mechanism by which antimuscarinics improve the symptoms of OAB remains to be elucidated. Animal studies suggest that antimuscarinics may exert an inhibitory effect on afferent nerves without an effect on detrusor contraction. A release of acetylcholine from the urothelium has been demonstrated in isolated human bladder. In addition, muscarinic receptors (MRs) were found in the urothelium and suburothelial myofibroblasts, suggesting a role for MR mechanisms in urothelial sensory function. Acetylcholine released during the storage phase could be expected to enhance the myogenic contractile activity of the detrusor, which can generate afferent signals. It is suggested that antimuscarinics may decrease bladder afferent activity by blocking MR in the above sites, thereby improving OAB symptoms.