Functional innervation of Guinea-pig bladder interstitial cells of cajal subtypes: neurogenic stimulation evokes in situ calcium transients

Mechanotransduction in the urothelium: ATP signalling and mechanoreceptors

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

Somatic mutations of CADM1 in aldosterone-producing adenomas and gap junction-dependent regulation of aldosterone production

Aldosterone-producing adenomas (APAs) are the commonest curable cause of hypertension. Most have gain-of-function somatic mutations of ion channels or transporters. Herein we report the discovery, replication and phenotype of mutations in the neuronal cell adhesion gene CADM1. Independent whole exome sequencing of 40 and 81 APAs found intramembranous p.Val380Asp or p.Gly379Asp variants in two patients whose hypertension and periodic primary aldosteronism were cured by adrenalectomy. Replication identified two more APAs with each variant (total, n = 6). The most upregulated gene (10- to 25-fold) in human adrenocortical H295R cells transduced with the mutations (compared to wildtype) was CYP11B2 (aldosterone synthase), and biological rhythms were the most differentially expressed process. CADM1 knockdown or mutation inhibited gap junction (GJ)-permeable dye transfer. GJ blockade by Gap27 increased CYP11B2 similarly to CADM1 mutation. Human adrenal zona glomerulosa (ZG) expression of GJA1 (the main GJ protein) was patchy, and annular GJs (sequelae of GJ communication) were less prominent in CYP11B2-positive micronodules than adjacent ZG. Somatic mutations of CADM1 cause reversible hypertension and reveal a role for GJ communication in suppressing physiological aldosterone production.

Imatinib Mesylate Reduces Voiding Frequency in Female Mice With Acute Cyclophosphamide-Induced Cystitis

Lamina propria interstitial cells that express the tyrosine kinase receptor, platelet-derived growth factor receptor alpha (PDGFRα) may play a role in urinary sensory signaling. Imatinib mesylate, also referred to as imatinib, is a tyrosine kinase inhibitor that can inhibit PDGFRα and has been widely used in urological research. We evaluated the functional effects of imatinib administration (via oral gavage or intravesical infusion) with two different experimental designs (prevention and treatment), in a cyclophosphamide (CYP)-induced cystitis (acute, intermediate, and chronic), male and female rodent model using conscious cystometry and somatic sensitivity testing. Imatinib significantly (0.0001 ≤ p ≤ 0.05) decreased voiding frequency and increased bladder capacity in acute CYP-induced cystitis, by the prevention (females) and treatment (females and males) designs. Imatinib was not effective in preventing or treating intermediate or chronic CYP-induced cystitis in either sex. Interestingly, in the prevention experiments, imatinib administration increased (0.0001 ≤ p ≤ 0.01) voiding frequency and decreased bladder capacity in control mice. However, in the treatment experiments, imatinib administration decreased (0.01 ≤ p ≤ 0.05) voiding frequency and increased bladder capacity in control mice. Bladder function improvements observed with imatinib treatment in acute CYP-induced cystitis mice remained and additionally improved with a second dose of imatinib 24 hours after CYP treatment. Imatinib administration did not affect pelvic somatic sensitivity in female mice with acute CYP-induced cystitis. Our studies suggest that (1) imatinib improves bladder function in mice with acute CYP-induced cystitis with a prevention and treatment design and (2) interstitial cells may be a useful target to improve bladder function in cystitis.

Imatinib Mesylate Reduces Neurotrophic Factors and pERK and pAKT Expression in Urinary Bladder of Female Mice With Cyclophosphamide-Induced Cystitis

Imatinib mesylate is a tyrosine kinase inhibitor that inhibits platelet-derived growth factor receptor (PDGFR)-α, -β, stem cell factor receptor (c-KIT), and BCR-ABL. PDGFRα is expressed in a subset of interstitial cells in the lamina propria (LP) and detrusor muscle of the urinary bladder. PDGFRα + interstitial cells may contribute to bladder dysfunction conditions such as interstitial cystitis/bladder pain syndrome (IC/BPS) or overactive bladder (OAB). We have previously demonstrated that imatinib prevention via oral gavage or treatment via intravesical infusion improves urinary bladder function in mice with acute (4 hour, h) cyclophosphamide (CYP)-induced cystitis. Here, we investigate potential underlying mechanisms mediating the bladder functional improvement by imatinib using a prevention or treatment experimental design. Using qRT-PCR and ELISAs, we examined inflammatory mediators (NGF, VEGF, BDNF, CCL2, IL-6) previously shown to affect bladder function in CYP-induced cystitis. We also examined the distribution of phosphorylated (p) ERK and pAKT expression in the LP with immunohistochemistry. Imatinib prevention significantly (0.0001 ≤ p ≤ 0.05) reduced expression for all mediators examined except NGF, whereas imatinib treatment was without effect. Imatinib prevention and treatment significantly (0.0001 ≤ p ≤ 0.05) reduced pERK and pAKT expression in the upper LP (U. LP) and deeper LP (D. LP) in female mice with 4 h CYP-induced cystitis. Although we have previously demonstrated that imatinib prevention or treatment improves bladder function in mice with cystitis, the current studies suggest that reductions in inflammatory mediators contribute to prevention benefits of imatinib but not the treatment benefits of imatinib. Differential effects of imatinib prevention or treatment on inflammatory mediators may be influenced by the route and frequency of imatinib administration and may also suggest other mechanisms (e.g., changes in transepithelial resistance of the urothelium) through which imatinib may affect urinary bladder function following CYP-induced cystitis.

Purinergic signalling in the urinary bladder - When function becomes dysfunction

Knowledge of the participation of ATP and related purines in urinary tract physiology has been established over the last five decades through the work of many independent groups, inspired by, and building on the pioneering studies of Professor Geoffrey Burnstock and his coworkers. As part of a series of reviews in this tribute edition, the present article summarises our current understanding of purines and purinergic signalling in modulating and regulating urinary tract function. Purinergic mechanisms underlying the origin of bladder pain; sensations of bladder filling and urinary tract motility; and regulation of detrusor smooth muscle contraction are described, encompassing the relevant history of discovery and consolidation of knowledge as methodologies and pharmacological tools have developed. We consider normal physiology, including development and ageing and then move to pathophysiology, discussing the causal and consequential contribution of purinergic signalling mechanism and their constituent components (receptors, signal transduction, effector molecules) to bladder dysfunction.

Role of Ano1 Ca2+-activated Cl- channels in generating urethral tone

Urinary continence is maintained in the lower urinary tract by the contracture of urethral sphincters, including smooth muscle of the internal urethral sphincter. These contractions occlude the urethral lumen, preventing urine leakage from the bladder to the exterior. Over the past 20 years, research on the ionic conductances that contribute to urethral smooth muscle contractility has greatly accelerated. A debate has emerged over the role of interstitial cell of Cajal (ICC)-like cells in the urethra and their expression of Ca²⁺-activated Cl^- channels encoded by anoctamin-1 [Ano1; transmembrane member 16 A (Tmem16a) gene]. It has been proposed that Ano1 channels expressed in urethral ICC serve as a source of depolarization for smooth muscle cells, increasing their excitability and contributing to tone. Although a clear role for Ano1 channels expressed in ICC is evident in other smooth muscle organs, such as the gastrointestinal tract, the role of these channels in the urethra is unclear, owing to differences in the species (rabbit, rat, guinea pig, sheep, and mouse) examined and experimental approaches by different groups. The importance of clarifying this situation is evident as effective targeting of Ano1 channels may lead to new treatments for urinary incontinence. In this review, we summarize the key findings from different species on the role of ICC and Ano1 channels in urethral contractility. Finally, we outline proposals for clarifying this controversial and important topic by addressing how cell-specific optogenetic and inducible cell-specific genetic deletion strategies coupled with advances in Ano1 channel pharmacology may clarify this area in future studies.NEW & NOTEWORTHY Studies from the rabbit have shown that anoctamin-1 (Ano1) channels expressed in urethral interstitial cells of Cajal (ICC) serve as a source of depolarization for smooth muscle cells, increasing excitability and tone. However, the role of urethral Ano1 channels is unclear, owing to differences in the species examined and experimental approaches. We summarize findings from different species on the role of urethral ICC and Ano1 channels in urethral contractility and outline proposals for clarifying this topic using cell-specific optogenetic approaches.

Constitutively active HCN channels constrain detrusor excitability and modulate evoked contractions of human bladder

OBJECTIVE

Expression of Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels is reported in bladder, but the functional role remains unsettled. Here, we immunolocalized the HCN1 and HCN4 subtype in human bladder and investigated their functional significance.

METHODS

Bladder procured from ten organ donors was dissected into mucosa (containing urothelium and submucosa) and detrusor for double immunofluorescence of HCN1 and 4 subtypes with gap junction and neural proteins together with isometric tension recordings. Mucosa intact and denuded detrusor strips were stretched to a basal tension of 10 mN for eliciting either tetrodotoxin (TTX) resistant spontaneous, carbachol evoked contractions and TTX sensitive electrical field stimulated (EFS), pre and post-addition of HCN blocker, ZD7288 or the activator, Lamotrigine or the cholinesterase inhibitor, Neostigmine.

RESULTS

Double immunofluorescence revealed immunolocalization of HCN1 and HCN4 subtype with calcitonin gene related peptide (CGRP), choline acetyl transferase and gap junction proteins in mucosa and detrusor. Removal of mucosa significantly raised the resting tension and the force of spontaneous contractions upon cumulative addition of ZD7288 in micromolar range relative to Lamotrigine treated strips (P<0.05). ZD7288 [10 nM] did not affect the contractile response evoked by EFS or carbachol, but the addition of ZD7288 [10 nM] in presence of Neostigmine [1 µM] significantly enhanced the atropine and TTX sensitive EFS evoked contractions of mucosa denuded strips.

CONCLUSIONS

Overall, HCN channels immunolocalized in mucosa, smooth muscle, gap junctions and nerve fibers exert a tonic constraint on detrusor excitability, enable spatio-temporal integration of evoked contractions and constrain the release of neurotransmitters, respectively. In contrast to the pacemaker role in other organs, findings argue for a non-pacemaking role of HCN channels in human bladder.

A Novel in situ Approach to Studying Detrusor Smooth Muscle Cells in Mice

The aim of our study was to develop a novel approach to investigating mouse detrusor smooth muscle cell (SMC) physiological activity, utilizing an acute tissue dissection technique and confocal calcium imaging. The bladder of a sacrificed adult female NMRI mouse was dissected. We used light and transmission electron microscopy to assess morphology of SMCs within the tissue. Calcium imaging in individual SMCs was performed using confocal microscopy during stimulation with increasing concentrations of carbamylcholine (CCh). SMCs were identified according to their morphology and calcium activity. We determined several parameters describing the SMC responses: delays to response, recruitment, relative activity, and contraction of the tissue. CCh stimulation revealed three different SMC phenotypes: spontaneously active SMCs with and without CCh-enhanced activity and SMCs with CCh-induced activity only. SMCs were recruited into an active state in response to CCh-stimulation within a narrow range (1-25 µM); causing activation of virtually all SMCs. Maximum calcium activity of SMCs was at about 25 µM, which coincided with a visible tissue contraction. Finally, we observed shorter time lags before response onsets with higher CCh concentrations. In conclusion, our novel in situ approach proved to be a robust and reproducible method to study detrusor SMC morphology and physiology.

Spontaneous Activity and the Urinary Bladder

The urinary bladder has two functions: to store urine, when it is relaxed and highly compliant; and void its contents, when intravesical pressure rises due to co-ordinated contraction of detrusor smooth muscle in the bladder wall. Superimposed on this description are two observations: (1) the normal, relaxed bladder develops small transient increases of intravesical pressure, mirrored by local bladder wall movements; (2) pathological, larger pressure variations (detrusor overactivity) can occur that may cause involuntary urine loss and/or detrusor overactivity. Characterisation of these spontaneous contractions is important to understand: how normal bladder compliance is maintained during filling; and the pathophysiology of detrusor overactivity. Consideration of how spontaneous contractions originate should include the structural complexity of the bladder wall. Detrusor smooth muscle layer is overlain by a mucosa, itself a complex structure of urothelium and a lamina propria containing sensory nerves, micro-vasculature, interstitial cells and diffuse muscular elements.Several theories, not mutually exclusive, have been advanced for the origin of spontaneous contractions. These include intrinsic rhythmicity of detrusor muscle; modulation by non-muscular pacemaking cells in the bladder wall; motor input to detrusor by autonomic nerves; regulation of detrusor muscle excitability and contractility by the adjacent mucosa and spontaneous contraction of elements of the lamina propria. This chapter will consider evidence for each theory in both normal and overactive bladder and how their significance may vary during ageing and development. Further understanding of these mechanisms may also identify novel drug targets to ameliorate the clinical consequences of large contractions associated with detrusor overactivity.

Modulation of Bladder Wall Micromotions Alters Intravesical Pressure Activity in the Isolated Bladder

Micromotions are phasic contractions of the bladder wall. During urine storage, such phasic activity has little effect on intravesical pressure, however, changed motile activity may underlie urodynamic observations such as detrusor overactivity. The potential for bladder motility to affect pressure reflects a summation of the overall movements, comprising the initiation, propagation, and dissipation components of micromotions. In this study, the influence of initiation of micromotions was investigated using calcium activated chloride channel blocker niflumic acid, and the effect of propagation using blockers of gap junctions. The overall bladder tone was modulated using isoprenaline. Isolated tissue strips and whole bladder preparations from juvenile rats were used. 18β-glycyrrhetinic acid was used to block gap junctions, reducing the amplitude and frequency of micromotions in in vitro and ex vivo preparations. Niflumic acid reduced the frequency of micromotions but had no effect on the amplitude of pressure fluctuations. Isoprenaline resulted in a reduction in pressure fluctuations and a decrease in pressure baseline. Using visual video data analysis, bladder movement was visible, irrespective of lack of pressure changes, which persisted during bladder relaxation. However, micromotions propagated over shorter distances and the overall bladder tone was reduced. All these results suggest that phasic activity of the bladder can be characterised by a combination of initiation and propagation of movement, and overall bladder tone. At any given moment, intravesical pressure recordings are an integration of these parameters. This synthesis gives insight into the limitations of clinical urodynamics, where intravesical pressure is the key indicator of detrusor activity.

Acute radiation impacts contractility of guinea-pig bladder strips affecting mucosal-detrusor interactions

Radiation-induced bladder toxicity is associated with radiation therapy for pelvic malignancies, arising from unavoidable irradiation of neighbouring normal bladder tissue. This study aimed to investigate the acute impact of ionizing radiation on the contractility of bladder strips and identify the radiation-sensitivity of the mucosa vs the detrusor. Guinea-pig bladder strips (intact or mucosa-free) received ex vivo sham or 20Gy irradiation and were studied with in vitro myography, electrical field stimulation and Ca2+-fluorescence imaging. Frequency-dependent, neurogenic contractions in intact strips were reduced by irradiation across the force-frequency graph. The radiation-difference persisted in atropine (1μM); subsequent addition of PPADs (100μM) blocked the radiation effect at higher stimulation frequencies and decreased the force-frequency plot. Conversely, neurogenic contractions in mucosa-free strips were radiation-insensitive. Radiation did not affect agonist-evoked contractions (1μM carbachol, 5mM ATP) in intact or mucosa-free strips. Interestingly, agonist-evoked contractions were larger in irradiated mucosa-free strips vs irradiated intact strips suggesting that radiation may have unmasked an inhibitory mucosal element. Spontaneous activity was larger in control intact vs mucosa-free preparations; this difference was absent in irradiated strips. Spontaneous Ca2+-transients in smooth muscle cells within tissue preparations were reduced by radiation. Radiation affected neurogenic and agonist-evoked bladder contractions and also reduced Ca2+-signalling events in smooth muscle cells when the mucosal layer was present. Radiation eliminated a positive modulatory effect on spontaneous activity by the mucosa layer. Overall, the findings suggest that radiation impairs contractility via mucosal regulatory mechanisms independent of the development of radiation cystitis.

What are the origins and relevance of spontaneous bladder contractions? ICI-RS 2017

INTRODUCTION

Storage phase bladder activity is a counter-intuitive observation of spontaneous contractions. They are potentially an intrinsic feature of the smooth muscle, but interstitial cells in the mucosa and the detrusor itself, as well as other muscular elements in the mucosa may substantially influence them. They are identified in several models explaining lower urinary tract dysfunction.

METHODS

A consensus meeting at the International Consultation on Incontinence Research Society (ICI-RS) 2017 congress considered the origins and relevance of spontaneous bladder contractions by debating which cell type(s) modulate bladder spontaneous activity, whether the methodologies are sufficiently robust, and implications for healthy and abnormal lower urinary tract function.

RESULTS

The identified research priorities reflect a wide range of unknown aspects. Cellular contributions to spontaneous contractions in detrusor smooth muscle are still uncertain. Accordingly, insight into the cellular physiology of the bladder wall, particularly smooth muscle cells, interstitial cells, and urothelium, remains important. Upstream influences, such as innervation, endocrine, and paracrine factors, are particularly important. The cellular interactions represent the key understanding to derive the integrative physiology of organ function, notably the nature of signalling between mucosa and detrusor layers. Indeed, it is still not clear to what extent spontaneous contractions generated in isolated preparations mirror their normal and pathological counterparts in the intact bladder. Improved models of how spontaneous contractions influence pressure generation and sensory nerve function are also needed.

CONCLUSIONS

Deriving approaches to robust evaluation of spontaneous contractions and their influences for experimental and clinical use could yield considerable progress in functional urology.

Rhythmic Calcium Events in the Lamina Propria Network of the Urinary Bladder of Rat Pups

The lamina propria contains a dense network of cells, including interstitial cells (ICs), that may play a role in bladder function by modulating communication between urothelium, nerve fibers and smooth muscle or acting as pacemakers. Transient receptor potential vanilloid 4 (TRPV4) channels allow cation influx and may be involved in sensing stretch or chemical irritation in urinary bladder. Urothelium was removed from rats (P0-Adult), cut into strips, and loaded with a Ca²⁺ fluorescent dye (Fluo-2 AM leak resistant or Cal 520) for 90 min (35-37°C) to measure Ca²⁺ events. Ca²⁺ events were recorded for a period of 60 seconds (s) in control and after drug treatment. A heterogeneous network of cells was identified at the interface of the urothelium and lamina propria of postnatal rat pups, aged ≤ postnatal (P) day 21, with diverse morphology (round, fusiform, stellate with numerous projections) and expressing platelet-derived growth factor receptor alpha (PDGFRα)- and TRPV4-immunoreactivity (IR). Ca²⁺ transients occurred at a slow frequency with an average interval of 30 ± 8.6 s. Waveform analyses of Ca²⁺ transients in cells in the lamina propria network revealed long duration Ca²⁺ events with slow upstrokes. We observed slow propagating waves of activity in the lamina propria network that displayed varying degrees of coupling. Application of the TRPV4 agonist, GSK1016790 (100 nM), increased the duration of Ca²⁺ events, the number of cells with Ca²⁺ events and the integrated Ca²⁺ activity corresponding to propagation of activity among cells in the lamina propria network. However, GSK2193874 (1 μM), a potent antagonist of TRPV4 channels, was without effect. ATP (1 μM) perfusion increased the number of cells in the lamina propria exhibiting Ca²⁺ events and produced tightly coupled network activity. These findings indicate that ATP and TRPV4 can activate cells in the laminar propria network, leading to the appearance of organized propagating wavefronts.

The Mystery of the Interstitial Cells in the Urinary Bladder

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

The Influence of Resiniferatoxin (RTX) and Tetrodotoxin (TTX) on the Distribution, Relative Frequency, and Chemical Coding of Noradrenergic and Cholinergic Nerve Fibers Supplying the Porcine Urinary Bladder Wall

The present study investigated the influence of intravesically instilled resiniferatoxin (RTX) or tetrodotoxin (TTX) on the distribution, number, and chemical coding of noradrenergic and cholinergic nerve fibers (NF) supplying the urinary bladder in female pigs. Samples from the bladder wall were processed for double-labelling immunofluorescence with antibodies against cholinergic and noradrenergic markers and some other neurotransmitter substances. Both RTX and TTX caused a significant decrease in the number of cholinergic NF in the urinary bladder wall (in the muscle coat, submucosa, and beneath the urothelium). RTX instillation resulted in a decrease in the number of noradrenergic NF in the submucosa and urothelium, while TTX treatment caused a significant increase in the number of these axons in all the layers. The most remarkable changes in the chemical coding of the NF comprised a distinct decrease in the number of the cholinergic NF immunoreactive to CGRP (calcitonin gene-related peptide), nNOS (neuronal nitric oxide synthase), SOM (somatostatin) or VIP (vasoactive intestinal polypeptide), and an increase in the number of noradrenergic NF immunopositive to GAL (galanin) or nNOS, both after RTX or TTX instillation. The present study is the first to suggest that both RTX and TTX can modify the number of noradrenergic and cholinergic NF supplying the porcine urinary bladder.

Proliferation of Interstitial Cells in the Cyclophosphamide-Induced Cystitis and the Preventive Effect of Imatinib

Cyclophosphamide- (CYP-) induced cystitis in the rat is a well-known model of bladder inflammation that leads to an overactive bladder, a process that appears to involve enhanced nitric oxide (NO) production. We investigated the changes in the number and distribution of interstitial cells (ICs) and in the expression of endothelial NO synthase (eNOS) in the bladder and urethra of rats subjected to either intermediate or chronic CYP treatment. Pronounced hyperplasia and hypertrophy of ICs were evident within the lamina propria and in the muscle layer. IC immunolabeling with CD34, PDGFRα, and vimentin was enhanced, as reflected by higher colocalization indexes of the distinct pairs of markers. Moreover, de novo expression of eNOS was evident in vimentin and CD34 positive ICs. Pretreatment with the receptor tyrosine kinase inhibitor Imatinib prevented eNOS expression and ICs proliferation, as well as the increased voiding frequency and urinary tract weight provoked by CYP. As similar results were obtained in the urethra, urethritis may contribute to the uropathology of CYP-induced cystitis.

The Influence of Tetrodotoxin (TTX) on the Distribution and Chemical Coding of Caudal Mesenteric Ganglion (CaMG) Neurons Supplying the Porcine Urinary Bladder

The treatment of micturition disorders creates a serious problem for urologists. Recently, new therapeutic agents, such as neurotoxins, are being considered for the therapy of urological patients. The present study investigated the chemical coding of caudal mesenteric ganglion (CaMG) neurons supplying the porcine urinary bladder after intravesical instillation of tetrodotoxin (TTX). The CaMG neurons were visualized with retrograde tracer Fast blue (FB) and their chemical profile was disclosed with double-labeling immunohistochemistry using antibodies against tyrosine hydroxylase (TH), neuropeptide Y (NPY), vasoactive intestinal polypeptide (VIP), somatostatin (SOM), calbindin (CB), galanin (GAL) and neuronal nitric oxide synthase (nNOS). It was found that in both the control (n = 6) and TTX-treated pigs (n = 6), the vast majority (92.6% ± 3.4% and 88.8% ± 2%, respectively) of FB-positive (FB+) nerve cells were TH+. TTX instillation caused a decrease in the number of FB+/TH+ neurons immunopositive to NPY (88.9% ± 5.3% in the control animals vs. 10.6% ± 5.3% in TTX-treated pigs) or VIP (1.7% ± 0.6% vs. 0%), and an increase in the number of FB+/TH+ neurons immunoreactive to SOM (8.8% ± 1.6% vs. 39% ± 12.8%), CB (1.8% ± 0.7% vs. 12.6% ± 2.7%), GAL (1.7% ± 0.8% vs. 10.9% ± 2.6%) or nNOS (0% vs. 1.1% ± 0.3%). The present study is the first to suggest that TTX modifies the chemical coding of CaMG neurons supplying the porcine urinary bladder.

Calcium Signaling in Interstitial Cells: Focus on Telocytes

In this review, we describe the current knowledge on calcium signaling pathways in interstitial cells with a special focus on interstitial cells of Cajal (ICCs), interstitial Cajal-like cells (ICLCs), and telocytes. In detail, we present the generation of Ca²⁺ oscillations, the inositol triphosphate (IP₃)/Ca²⁺ signaling pathway and modulation exerted by cytokines and vasoactive agents on calcium signaling in interstitial cells. We discuss the physiology and alterations of calcium signaling in interstitial cells, and in particular in telocytes. We describe the physiological contribution of calcium signaling in interstitial cells to the pacemaking activity (e.g., intestinal, urinary, uterine or vascular pacemaking activity) and to the reproductive function. We also present the pathological contribution of calcium signaling in interstitial cells to the aortic valve calcification or intestinal inflammation. Moreover, we summarize the current knowledge of the role played by calcium signaling in telocytes in the uterine, cardiac and urinary physiology, and also in various pathologies, including immune response, uterine and cardiac pathologies.

Low amplitude rhythmic contraction frequency in human detrusor strips correlates with phasic intravesical pressure waves

PURPOSE

Low amplitude rhythmic contractions (LARC) occur in detrusor smooth muscle and may play a role in storage disorders such as overactive bladder and detrusor overactivity. The purpose of this study was to determine whether LARC frequencies identified in vitro from strips of human urinary bladder tissue correlate with in vivo LARC frequencies, visualized as phasic intravesical pressure (p _ves) waves during urodynamics (UD).

METHODS

After IRB approval, fresh strips of human urinary bladder were obtained from patients. LARC was recorded with tissue strips at low tension (<2 g) and analyzed by fast Fourier transform (FFT) to identify LARC signal frequencies. Blinded UD tracings were retrospectively reviewed for signs of LARC on the p _ves tracing during filling and were analyzed via FFT.

RESULTS

Distinct LARC frequencies were identified in 100% of tissue strips (n = 9) obtained with a mean frequency of 1.97 ± 0.47 cycles/min (33 ± 8 mHz). Out of 100 consecutive UD studies reviewed, 35 visually displayed phasic p _ves waves. In 12/35 (34%), real p _ves signals were present that were independent of abdominal activity. Average UD LARC frequency was 2.34 ± 0.36 cycles/min (39 ± 6 mHz) which was similar to tissue LARC frequencies (p = 0.50). A majority (83%) of the UD cohort with LARC signals also demonstrated detrusor overactivity.

CONCLUSIONS

During UD, a subset of patients displayed phasic p _ves waves with a distinct rhythmic frequency similar to the in vitro LARC frequency quantified in human urinary bladder tissue strips. Further refinements of this technique may help identify subsets of individuals with LARC-mediated storage disorders.

Transient contractions of urinary bladder smooth muscle are drivers of afferent nerve activity during filling

Activation of afferent nerves during urinary bladder (UB) filling conveys the sensation of UB fullness to the central nervous system (CNS). Although this sensory outflow is presumed to reflect graded increases in pressure associated with filling, UBs also exhibit nonvoiding, transient contractions (TCs) that cause small, rapid increases in intravesical pressure. Here, using an ex vivo mouse bladder preparation, we explored the relative contributions of filling pressure and TC-induced pressure transients to sensory nerve stimulation. Continuous UB filling caused an increase in afferent nerve activity composed of a graded increase in baseline activity and activity associated with increases in intravesical pressure produced by TCs. For each ∼4-mmHg pressure increase, filling pressure increased baseline afferent activity by ∼60 action potentials per second. In contrast, a similar pressure elevation induced by a TC evoked an ∼10-fold greater increase in afferent activity. Filling pressure did not affect TC frequency but did increase the TC rate of rise, reflecting a change in the length-tension relationship of detrusor smooth muscle. The frequency of afferent bursts depended on the TC rate of rise and peaked before maximum pressure. Inhibition of small- and large-conductance Ca(2+)-activated K(+) (SK and BK) channels increased TC amplitude and afferent nerve activity. After inhibiting detrusor muscle contractility, simulating the waveform of a TC by gently compressing the bladder evoked similar increases in afferent activity. Notably, afferent activity elicited by simulated TCs was augmented by SK channel inhibition. Our results show that afferent nerve activity evoked by TCs represents the majority of afferent outflow conveyed to the CNS during UB filling and suggest that the maximum TC rate of rise corresponds to an optimal length-tension relationship for efficient UB contraction. Furthermore, our findings implicate SK channels in controlling the gain of sensory outflow independent of UB contractility.

Neurogenic mechanisms in bladder and bowel ageing

The prevalence of both urinary and faecal incontinence, and also chronic constipation, increases with ageing and these conditions have a major impact on the quality of life of the elderly. Management of bladder and bowel dysfunction in the elderly is currently far from ideal and also carries a significant financial burden. Understanding how these changes occur is thus a major priority in biogerontology. The functions of the bladder and terminal bowel are regulated by complex neuronal networks. In particular neurons of the spinal cord and peripheral ganglia play a key role in regulating micturition and defaecation reflexes as well as promoting continence. In this review we discuss the evidence for ageing-induced neuronal dysfunction that might predispose to neurogenic forms of incontinence in the elderly.

Olfactory marker protein expression is an indicator of olfactory receptor-associated events in non-olfactory tissues

Olfactory receptor (OR)-associated events are mediated by well-conserved components in the olfactory epithelium, including olfactory G-protein (G_olf), adenylate cyclase III (ACIII), and olfactory marker protein (OMP). The expression of ORs has recently been observed in non-olfactory tissues where they are involved in monitoring extracellular chemical cues. The large number of OR genes and their sequence similarities illustrate the need to find an effective and simple way to detect non-olfactory OR-associated events. In addition, expression profiles and physiological functions of ORs in non-olfactory tissues are largely unknown. To overcome limitations associated with using OR as a target protein, this study used OMP with G_olf and ACIII as targets to screen for potential OR-mediated sensing systems in non-olfactory tissues. Here, we show using western blotting, real-time PCR, and single as well as double immunoassays that ORs and OR-associated proteins are co-expressed in diverse tissues. The results of immunohistochemical analyses showed OMP (+) cells in mouse heart and in the following cells using the corresponding marker proteins c-kit, keratin 14, calcitonin, and GFAP in mouse tissues: interstitial cells of Cajal of the bladder, medullary thymic epithelial cells of the thymus, parafollicular cells of the thyroid, and Leydig cells of the testis. The expression of ORs in OMP (+) tissues was analyzed using a refined microarray analysis and validated with RT-PCR and real-time PCR. Three ORs (olfr544, olfr558, and olfr1386) were expressed in the OMP (+) cells of the bladder and thyroid as shown using a co-immunostaining method. Together, these results suggest that OMP is involved in the OR-mediated signal transduction cascade with olfactory canonical signaling components between the nervous and endocrine systems. The results further demonstrate that OMP immunohistochemical analysis is a useful tool for identifying expression of ORs, suggesting OMP expression is an indicator of potential OR-mediated chemoreception in non-olfactory systems.

Calcium signalling in Cajal-like interstitial cells of the lower urinary tract

Interstitial cells of Cajal (ICC) serve several critical physiological roles in visceral smooth muscle organs, including acting as electrical pacemakers to modulate phasic contractile activity and as intermediaries in motor neurotransmission. The major roles of ICC have been described in the gastrointestinal tract, however, ICC-like cells (ICC-LC) can also be found in other visceral organs, including those of the lower urinary tract (LUT), where they provide similar functions, acting as electrical pacemakers and as intermediary cells involved in the modulation of neurotransmission to adjacent smooth muscle cells. The physiological functions of ICC-LC, in particular their role as pacemakers, relies on their ability to generate transient and propagating intracellular Ca(2+) events. The role of ICC-LC as pacemakers and neuromodulators in the LUT is increasingly apparent and the study of their intracellular Ca(2+) dynamics will provide a better understanding of their role in LUT excitability.

Interstitial cells: regulators of smooth muscle function

Smooth muscles are complex tissues containing a variety of cells in addition to muscle cells. Interstitial cells of mesenchymal origin interact with and form electrical connectivity with smooth muscle cells in many organs, and these cells provide important regulatory functions. For example, in the gastrointestinal tract, interstitial cells of Cajal (ICC) and PDGFRα(+) cells have been described, in detail, and represent distinct classes of cells with unique ultrastructure, molecular phenotypes, and functions. Smooth muscle cells are electrically coupled to ICC and PDGFRα(+) cells, forming an integrated unit called the SIP syncytium. SIP cells express a variety of receptors and ion channels, and conductance changes in any type of SIP cell affect the excitability and responses of the syncytium. SIP cells are known to provide pacemaker activity, propagation pathways for slow waves, transduction of inputs from motor neurons, and mechanosensitivity. Loss of interstitial cells has been associated with motor disorders of the gut. Interstitial cells are also found in a variety of other smooth muscles; however, in most cases, the physiological and pathophysiological roles for these cells have not been clearly defined. This review describes structural, functional, and molecular features of interstitial cells and discusses their contributions in determining the behaviors of smooth muscle tissues.

Macroscopic electrical propagation in the guinea pig urinary bladder

There is little knowledge about macroscopic electrical propagation in the wall of the urinary bladder. Recording simultaneously from a large number of extracellular electrodes is one technology that could be used to study the patterns of macroscopic electrical propagations. The urinary bladders from 14 guinea pigs were isolated and placed in an organ bath. A 16 × 4-electrode array was positioned at various sites on the serosal bladder surface, and recordings were performed at different intravesical volumes. In four experiments, carbachol (CCH; 10(-6) M), nifedipine (10 mM), or tetrodotoxin (TTX; 10(-6) M) was added to the superfusing fluid. After the experiments, the extracellular signals were analyzed and propagation maps were constructed. Electrical waves were detected at all sites on the bladder surface and propagated for a limited distance before terminating spontaneously. The majority of waves (>90%) propagated in the axial direction (i.e., from dome to base or vice versa). An increase in vesicle volume significantly decreased the conduction velocity (from 4.9 ± 1.5 to 2.7 ± 0.7 cm/s; P < 0.05). CCH increased, nifedipine decreased, while TTX had little effect on electrical activities. In addition, a new electrical phenomenon, termed a "patch," was discovered whereby a simultaneous electrical deflection was detected across an area of the bladder surface. Two types of electrical activities were detected on the bladder surface: 1) electrical waves propagating preferentially in the axial direction and 2) electrical patches. The propagating electrical waves could form the basis for local spontaneous contractions in the bladder during the filling phase.