Effects of imatinib mesylate (Glivec) as a c-kit tyrosine kinase inhibitor in the guinea-pig urinary bladder

Low-Intensity Extracorporeal Shock Wave Therapy Ameliorates Detrusor Hyperactivity with Impaired Contractility via Transient Potential Vanilloid Channels: A Rat Model for Ovarian Hormone Deficiency

This study explores low-intensity extracorporeal shock wave therapy (LiESWT)'s efficacy in alleviating detrusor hyperactivity with impaired contractility (DHIC) induced by ovarian hormone deficiency (OHD) in ovariectomized rats. The rats were categorized into the following four groups: sham group; OVX group, subjected to bilateral ovariectomy (OVX) for 12 months to induce OHD; OVX + SW4 group, underwent OHD for 12 months followed by 4 weeks of weekly LiESWT; and OVX + SW8 group, underwent OHD for 12 months followed by 8 weeks of weekly LiESWT. Cystometrogram studies and voiding behavior tracing were used to identify the symptoms of DHIC. Muscle strip contractility was evaluated through electrical-field, carbachol, ATP, and KCl stimulations. Western blot and immunofluorescence analyses were performed to assess the expressions of various markers related to bladder dysfunction. The OVX rats exhibited significant bladder deterioration and overactivity, alleviated by LiESWT. LiESWT modified transient receptor potential vanilloid (TRPV) channel expression, regulating calcium concentration and enhancing bladder capacity. It also elevated endoplasmic reticulum (ER) stress proteins, influencing ER-related Ca2+ channels and receptors to modulate detrusor muscle contractility. OHD after 12 months led to neuronal degeneration and reduced TRPV1 and TRPV4 channel activation. LiESWT demonstrated potential in enhancing angiogenic remodeling, neurogenesis, and receptor response, ameliorating DHIC via TRPV channels and cellular signaling in the OHD-induced DHIC rat model.

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.

Cyclic Stretch Promotes Proliferation and Contraction of Human Bladder Smooth Muscle Cells by Cajal-Mediated c-kit Expression in Interstitial Cells

Background

The present study was performed to assess the effect of mechanical stretch on the proliferation and contractile function of hBSMCs.

Material/Methods

hBSMCs and ICCs were seeded at 8×10⁴ cells/well in 6-well silicone elastomer-bottomed culture plates coated with type I collagen, and grown to 80% confluence in DMEM/10% FBS and a 5% CO₂ humidified atmosphere at 37°C. Cells of hBSMCs and hBSMCs/ICCs of co-culture were then subjected to continuous cycles of stretch-relaxation using a computer-driven, stretch-inducing device. The treated concentration of imatinib was 10 μM. Mechanisms underlying observed hBSMCs contraction were examined using Western blotting and RT-PCR. The 0.1 μM carbachol was separately added to the experimental groups, and 300 s was recorded by laser scanning confocal microscope.

Results

We found that mechanical stretch increased contraction and proliferation of hBSMCs. Calcium ion activity increased significantly after mechanical stretch. The number of hBSMCs was significantly increased after the combination mechanical stretch with ICCs treatment. After combination mechanical stretch with hBSMCs/ICCs treatment, the mRNA and protein level of M2, M3, and c-kit were significantly increased. After combination of mechanical stretch with no imatinib treatment, the proliferation of hBSMCs was higher than others, and the mRNA and protein level of M2 and M3 were significantly increased.

Conclusions

We revealed that ICCs could promote hBSMC proliferation and contraction, and cyclic stretch could promote acetylcholine receptor M2 and M3 caused by c-kit in the ICCs, which promoted the contraction of hBSMCs.

Investigation of the Syncytial Nature of Detrusor Smooth Muscle as a Determinant of Action Potential Shape

Unlike most excitable cells, certain syncytial smooth muscle cells are known to exhibit spontaneous action potentials of varying shapes and sizes. These differences in shape are observed even in electrophysiological recordings obtained from a single cell. The origin and physiological relevance of this phenomenon are currently unclear. The study presented here aims to test the hypothesis that the syncytial nature of the detrusor smooth muscle tissue contributes to the variations in the action potential profile by influencing the superposition of the passive and active signals. Data extracted from experimental recordings have been compared with those obtained through simulations. The feature correlation studies on action potentials obtained from the experimental recordings suggest the underlying presence of passive signals, called spontaneous excitatory junction potentials (sEJPs). Through simulations, we are able to demonstrate that the syncytial organization of the cells, and the variable superposition of the sEJPs with the "native action potential", contribute to the diversity in the action potential profiles exhibited. It could also be inferred that the fraction of the propagated action potentials is very low in the detrusor. It is proposed that objective measurements of spontaneous action potential profiles can lead to a better understanding of bladder physiology and pathology.

Increased Piezo1 channel activity in interstitial Cajal-like cells induces bladder hyperactivity by functionally interacting with NCX1 in rats with cyclophosphamide-induced cystitis

The Piezo1 channel is a mechanotransduction mediator, and Piezo1 abnormalities have been linked to several clinical disorders. However, the role of the Piezo1 channel in cystitis-associated bladder dysfunction has not been documented. The current study aimed to discover the functional role of this channel in regulating bladder activity during cyclophosphamide (CYP)-induced cystitis. One hundred four female rats were randomly assigned to the control, CYP-4h, CYP-48h and CYP-8d groups. CYP successfully induced acute or chronic cystitis in these rats. CYP treatment for 48h or 8d significantly increased Piezo1 channel expression in bladder interstitial Cajal-like cells (ICC-LCs), and the increase in CYP-8d rats was more prominent. In addition, 2.5 μM Grammostola spatulata mechanotoxin 4 (GsMTx4) significantly attenuated bladder hyperactivity in CYP-8d rats by inhibiting the Piezo1 channel in bladder ICC-LCs. Furthermore, by using GsMTx4 and siRNA targeting the Piezo1 channel, we demonstrated that hypotonic stress-induced Piezo1 channel activation significantly triggered Ca²⁺ and Na⁺ influx into bladder ICC-LCs during CYP-induced chronic cystitis. In addition, the Piezo1 channel functionally interacted with the relatively activated reverse mode of Na⁺/Ca²⁺ exchanger 1 (NCX1) in bladder ICC-LCs from CYP-8d rats. In conclusion, we suggest that the functional role of the Piezo1 channel in CYP-induced chronic cystitis is based on its synergistic effects with NCX1, which can significantly enhance [Ca²⁺]_i and result in Ca²⁺ overload in bladder ICC-LCs, indicating that the Piezo1 channel and NCX1 are potential novel therapeutic targets for chronic cystitis-associated bladder hyperactivity.

A protein that controls the passage of ions through cell membranes is implicated in interstitial cystitis/painful bladder syndrome (IC/PBS). This condition causes chronic pelvic pain and increased urinary frequency and urgency. Current treatment options are unsatisfactory. Researchers led by Longkun Li at the Third Military Medical University in Chongqing, China, and Mingjia Tan at the University of Michigan, Ann Arbor, USA, studied the role of this membrane channel protein, called Piezo1. Increased activity of Piezo1 was linked to bladder hyperactivity in rats with drug-induced cystitis. The research also identified a synergistic interaction between Piezo1 and a second membrane channel protein. A drug that inhibits Piezo1 activity reduced bladder hyperactivity in the rats. Drugs targeting these two proteins might help to treat the chronic cystitis of patients with IC/PBS.

Decreased hyperpolarization-activated cyclic nucleotide-gated channels are involved in bladder dysfunction associated with spinal cord injury

Spinal cord injury (SCI) leads to bereft voluntary control of bladder, but the possible role of spontaneous excited system in bladder of SCI patients is poorly understood. Hyper polarization-activated cyclic nucleotide-gated (HCN) channels are deemed to regulate the spontaneous contraction of bladder, our study explored the functional role of HCN channels in SCI induced neurogenic bladder. Sixty female Sprague-Dawley rats were randomized into control, sham and SCI groups. Rat models subjected to SCI at S2 levels were successfully established and were assessed using hematoxylin and eosin staining and cystometry. In SCI rats, the mRNA and protein expression levels of HCN channels and the I_h density were significantly reduced, and expression levels of several bladder HCN1 channel regulatory proteins were also significantly changed. The effects of 50 µM forskolin and 50 µM 8-bromoadenosine 3′,5′-cyclic monophosphate on [Ca²⁺]_i of isolated bladder interstitial cells of Cajal-like cells were significantly decreased in SCI rats. The spontaneous contractions in detrusor strips from SCI rats were significantly weakened. Furthermore, detrusor strips from SCI rats exhibited decreased tolerance to two doses of ZD7288 (10 and 50 µM). Taken together, our results indicate that the decreased bladder HCN channel expression and function induced by altered regulatory proteins are involved in the pathological process of SCI induced neurogenic bladder, which present HCN channels as valid therapeutic targets for treating this disease.

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.

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.

Spatiotemporal analysis of spontaneous myogenic contractions in the urinary bladder of the rabbit: timing and patterns reflect reported electrophysiology

The dynamics of propagating myogenic contractions in the wall of the resting ex vivo urinary bladder of the rabbit were characterized by spatiotemporal maps and related to cyclic variation in intravesical pressure (P_ves). Patches of propagating contractions (PPCs) enlarged and involuted in near synchrony with peaks in P_ves [mean 3.85  ± 0.3 cycles per minute (cpm)] and were preceded by regions of stretch. The maximum area of the bladder undergoing contraction (55.28 ± 2.65%) and the sizes of individual PPCs (42.61 ± 1.65 mm²) coincided with the peak in P_ves PPCs originated and propagated within temporary patch domains (TPDs) and comprised groups of nearly synchronous cyclic propagating individual contractions (PICs). The TPDs were located principally along the vertical axis of the anterior surface of the bladder. The sites of origin of PICs within PPCs were inconsistent, consecutive contractions often propagating in opposite directions along linear maps of strain rate. Similar patterns of movement occurred in areas of the anterior bladder wall that had been stripped of mucosa. P_ves varied cyclically with area of contraction and with the indices of aggregation of PPCs, indicating that they grew by peripheral enlargement and collision without annihilation. The synchronization of PICs within PPCs was sometimes lost, uncoordinated PICs then occurring irregularly (between 4 and 20 cpm) having little effect on P_ves We postulate that the formation and involution of PPCs within a TPD resulted from cyclic variation in excitation that increased the incidence and distance over which component PICs propagated.

Original Research: Combined model of bladder detrusor smooth muscle and interstitial cells

Although patients with lower urinary tract symptoms constitute a large and still growing population, understanding of bladder detrusor muscle physiology remains limited. Understanding the interactions between the detrusor smooth muscle cells and other bladder cell types (e.g. interstitial cells, IC) that may significantly contribute to coordinating and modulating detrusor contractions represents a considerable challenge. Computer modeling could help to elucidate some properties that are difficult to address experimentally; therefore, we developed in silico models of detrusor smooth muscle cell and interstitial cells, coupled through gap junctions. The models include all of the major ion conductances and transporters described in smooth muscle cell and interstitial cells in the literature. The model of normal detrusor muscle (smooth muscle cell and interstitial cells coupled through gap junctions) completely reproduced the experimental results obtained with detrusor strips in the presence of several pharmacological interventions (ryanodine, caffeine, nimodipine), whereas the model of smooth muscle cell alone (without interstitial cells) failed to reproduce the experimental results. Next, a model of overactive bladder, a highly prevalent clinical condition in both men and women with increasing incidence at older ages, was produced by modifying several processes as reported previously: a reduction of Ca(2+)-release through ryanodine receptors and a reduction of Ca(2+)-dependent K(+)-conductance with augmented gap junctional coupling. This model was also able to reproduce the pharmacological modulation of overactive bladder. In conclusion, a model of bladder detrusor muscle was developed that reproduced experimental results obtained in both normal and overactive bladder preparations. The results indicate that the non-smooth muscle cells of the detrusor (interstitial cells) contribute significantly to the contractile behavior of bladder detrusor muscle and should not be neglected. The model suggests that reduced Ca(2+)-release through ryanodine receptors and Ca(2+)-dependent K(+)-conductance together with augmented gap junctional coupling might play a major role in overactive bladder pathogenesis.

Spontaneous Contractile Activity of the Detrusor Muscle and Its Role in the Pathogenesis of Overactive Bladder Syndrome

There is accumulated evidence that spontaneous contractions (SCs) in the bladder wall are associated with afferent nerve firing in the bladder. The role of the urothelium in bladder sensation might be restricted to pathological conditions, such as interstitial cystitis or chemical cystitis in which the release of urothelium-derived mediators such as adenosine triphosphate is increased. Recent publications imply that SCs in bladders with detrusor overactivity due to spinal cord injury or bladder outlet obstruction are modulated by intracellular signal transduction mechanisms such as the RhoA/Rho-kinase pathway, denervation-supersensitivity to acetylcholine, changes in ion channel activity, enhanced gap-junctional intercellular communication, alterations in interstitial cells of Cajal, the actions of local mediators in the detrusor and the influence of the urothelium. Spontaneous contractions and possible consequent afferent nerve firing might participate in the generation of overactive bladder syndrome.

Anatomy and physiology of the lower urinary tract

Functions of the lower urinary tract to store and periodically eliminate urine are regulated by a complex neural control system in the brain, spinal cord, and peripheral autonomic ganglia that coordinates the activity of smooth and striated muscles of the bladder and urethral outlet. Neural control of micturition is organized as a hierarchic system in which spinal storage mechanisms are in turn regulated by circuitry in the rostral brainstem that initiates reflex voiding. Input from the forebrain triggers voluntary voiding by modulating the brainstem circuitry. Many neural circuits controlling the lower urinary tract exhibit switch-like patterns of activity that turn on and off in an all-or-none manner. The major component of the micturition switching circuit is a spinobulbospinal parasympathetic reflex pathway that has essential connections in the periaqueductal gray and pontine micturition center. A computer model of this circuit that mimics the switching functions of the bladder and urethra at the onset of micturition is described. Micturition occurs involuntarily during the early postnatal period, after which it is regulated voluntarily. Diseases or injuries of the nervous system in adults cause re-emergence of involuntary micturition, leading to urinary incontinence. The mechanisms underlying these pathologic changes are discussed.

Relationship between connexin43-derived gap junction proteins in the bladder and age-related detrusor underactivity in rats

AIMS

To confirm the mechanisms of age-associated detrusor underactivity (DU), we examined the differences in bladder activity and connexin-43 (Cx43)-derived gap junctions in the bladders of young and old rats.

MAIN METHODS

Female Sprague-Dawley rats aged 3months (young) and 12months (old) were used. Continuous cystometry was performed under urethane anesthesia in both ages of rats. In addition, isovolumetric cystometry was performed in young rats during the intravesical application of carbenoxolone, a gap junction blocker, to confirm the role of gap junction proteins in the bladder. Western blotting analyses were performed to assess Cx43 protein expression in the bladders of both groups of rats. Bladders were also analyzed using Masson's trichrome staining and immunostaining for Cx43.

KEY FINDINGS

Cystometric evaluations revealed that compared with young rats, bladder contractility was reduced by 27% and residual urine volume was significantly increased in old rats. However, the intercontraction intervals did not differ between the two groups. Under isovolumetric conditions, bladder contraction was suppressed after the intravesical application of carbenoxolone. In the bladders of old rats, increase of smooth muscle cell hypertrophy and fibrous tissue was observed compared with young rats. In association with these findings, immunostaining for smooth muscle Cx43 and its protein level were decreased by 28% compared with young rats.

SIGNIFICANCE

These results suggest that age-related DU might be caused by the downregulation of gap junctional intercellular communication in the bladder. Consequently, the normal signals that contribute to voiding function might not be transported between detrusor muscles.

Distribution of interstitial cells of Cajal in the neurogenic urinary bladder of children with myelomeningocele

PURPOSE

C-kit positive interstitial cells of Cajal (ICCs) play an important role in the regulation of the smooth muscle motility, acting as pacemakers to provide the slow wave activity in various organs. Recent studies have shown that c-kit positive ICCs are widely distributed in the urinary tract of animals and humans. The aim of our study was to examine the distribution of ICCs in the children's neurogenic bladder.

METHODS

An immunohistochemical study of specimens obtained from neurogenic urinary bladder (from the trigonum and the corpus) of children with meningomyelocele and during autopsy was performed using antibody against c-kit (CD 117). Histological morphometry of immunoexpression of c-kit positive ICCs was performed by means of an image analyzing system.

RESULTS

Our investigation demonstrated ICCs located in the vesical muscle layers. The distribution of those cells is different in the trigonum and the corpus of the urinary bladder. No remarkable differences were observed in c-kit immunoexpression between the neurogenic and the control group.

CONCLUSION

There was no difference in the distribution of ICCs in the urinary bladder of healthy children as compared to children with myelomeningocele. Biopsy revealed different distribution of ICCs in particular parts of the bladder (trigonum/ corpus) in both groups of children.

Interstitial cells of Cajal modulate the tone of the human internal anal sphincter in vitro

BACKGROUND

Interstitial cells of Cajal, expressing the proto-oncogene c-kit, have been shown to regulate the spontaneous activity of the gastrointestinal tract. They have been described in the human internal anal sphincter; however, their function is still unclear.

OBJECTIVE

We examined the effects of the c-kit tyrosine kinase inhibitor imatinib mesylate on sphincter strips to investigate the function of the interstitial cells.

DESIGN

This was a case series study.

SETTIGS

This was a single-center study conducted at the University of Oxford.

PATIENTS

Internal anal sphincter strips were collected from 10 patients undergoing abdominoperineal resection or proctectomy and mounted in organ bath. Responses to electrical field stimulation and chemical agents were monitored in the absence of drugs and after the administration of increasing doses of imatinib mesylate. Immunohistochemistry was performed to identify interstitial cells.

MAIN OUTCOME MEASURES

The role of the interstitial cells in the internal anal sphincter was assessed.

RESULTS

Imatinib mesylate significantly reduced the tone and the spontaneous activity of the strips. In the absence of drugs, the tone generated was 147.7 ± 33.0 mg/mg of tissue. Administration of ≥5 μM of imatinib mesylate caused a dose-dependent reduction in the tone. Strips exhibited spontaneous activity characterized by intermittent low-amplitude contractions superimposed on basal tone (135.6 ± 4.6 contractions in 10 minutes). Imatinib mesylate significantly reduced the number of contractions at concentration >5 μM. No differences were observed in the responses to electrical field stimulation, carbachol, or phenylephrine. Immunohistochemistry showed c-kit-positive cells.

LIMITATIONS

This study was limited by the relatively small number of patients enrolled and thus the difficulty of finding human tissue for laboratory studies.

CONCLUSIONS

Our results suggest that the interstitial cells modulate the tone and the spontaneous activity of the internal anal sphincter. This provides a foundation for new approaches to preclinical and clinical research. Moreover, these cells may represent a target for drugs inhibiting the c-kit receptor and provide a new approach for treating anorectal diseases.

Neural mechanisms underlying lower urinary tract dysfunction

This article summarizes anatomical, neurophysiological, and pharmacological studies in humans and animals to provide insights into the neural circuitry and neurotransmitter mechanisms controlling the lower urinary tract and alterations in these mechanisms in lower urinary tract dysfunction. The functions of the lower urinary tract, to store and periodically release urine, are dependent on the activity of smooth and striated muscles in the bladder, urethra, and external urethral sphincter. During urine storage, the outlet is closed and the bladder smooth muscle is quiescent. When bladder volume reaches the micturition threshold, activation of a micturition center in the dorsolateral pons (the pontine micturition center) induces a bladder contraction and a reciprocal relaxation of the urethra, leading to bladder emptying. During voiding, sacral parasympathetic (pelvic) nerves provide an excitatory input (cholinergic and purinergic) to the bladder and inhibitory input (nitrergic) to the urethra. These peripheral systems are integrated by excitatory and inhibitory regulation at the levels of the spinal cord and the brain. Therefore, injury or diseases of the nervous system, as well as disorders of the peripheral organs, can produce lower urinary tract dysfunction, leading to lower urinary tract symptoms, including both storage and voiding symptoms, and pelvic pain. Neuroplasticity underlying pathological changes in lower urinary tract function is discussed.

Cajal-like interstitial cells as a novel target in detrusor overactivity treatment: true or myth?

Introduction

The Cajal–like intestitial cells (ICCs) act as a pacemaker and are responsible for generating smooth muscle activity in the gastrointestinal tract (GI). Interstitial cells that resemble ICCs in the GI have been identified in the urinary bladder.

Materials and methods

This review is based on a systemic literature research. The medline/pubmed, scopus, embase, and Web of Science databases were browsed in order to identify original and review articles, as well as editorials relating to cajal–like cells, urinary bladder, detrusor overactivity, overactive bladder, glivec, etc. The controlled vocabulary of the Medical Subject Headings (MeSH) database was used to ensure the sensitivity of the searches. 40 papers met the criteria and were used for this review.

Results

Cajal cells lie in close proximity to the muscle cells, autonomic nerve endings, and urothelial cells. There is increasing evidence that ICCs play role in urinary tract dysfunction development (e.g. detrusor overactivity, primary obstructive megaureter, congenital ureteropelvic junction obstruction, etc.). ICCs may be responsible for generating electrical potentials and induction of detrusor muscle contractions. Novel pathomechanisms of detrusor overactivity development have been postulated, as follows: 1) the disturbance of spontaneous contractility caused by altered signal transduction of ICCs between nerves and detrusor muscle cells, and 2). the alteration in signal transduction between urothelium and afferent nerve endings via suburothelial ICCs. The c–kit receptor is not only a detection marker of these cells, but may also play a crucial role in the control of bladder function.

Conclusions

Cajal cells in urinary bladder suggest that the c–kit receptor may provide a novel target for treating detrusor overactivity. The review presents the current knowledge of ICCs, its role in urinary bladder function, and potential novel therapeutic strategy.

Effects of imatinib mesylate on the spontaneous activity generated by the guinea-pig prostate

What's known on the subject? and what does the study add?: Several studies have examined the functional role of tyrosine kinase receptors in the generation of spontaneous activity in various segments of the gastrointestinal and urogenital tracts through the application of its inhibitor, imatinib mesylate (Glivec®), but results are fairly inconsistent. This is the first study detailing the effects of imatinib mesylate on the spontaneous activity in the young and ageing prostate gland. As spontaneous electrical activity underlies the spontaneous rhythmic prostatic contractions that occur at rest, elucidating the mechanisms involved in the regulation of the spontaneous electrical activity and the resultant phasic contractions could conceivably lead to the identification of better targets and the development of more specific therapeutic agents to treat prostate conditions.

OBJECTIVE

To investigate the effect of imatinib mesylate, a tyrosine kinase receptor inhibitor, in the generation of spontaneous electrical and contractile activity in the young and ageing guinea-pig prostate.

MATERIALS AND METHODS

Standard tension and intracellular recording were used to measure spontaneous contractions and slow waves, respectively from the guinea-pig prostate at varying concentrations of imatinib mesylate (1-50 μm).

RESULTS

Imatinib mesylate (1-10 μm), did not significantly affect slow waves recorded in the prostate of both age groups but at 50 μm, the amplitude of slow waves from the ageing guinea-pig prostate was significantly reduced (P < 0.05, n = 5). In contrast, the amplitude of contractions across all concentrations in the young guinea-pig prostate was reduced to between 35% and 41% of control, while the frequency was reduced to 15.7% at 1 μm (n = 7), 49.8% at 5 μm (n = 10), 46.2% at 10 μm (n = 7) and 53.1% at 50 μm (n = 5). Similarly, imatinib mesylate attenuated the amplitude and slowed the frequency of contractions in ageing guinea-pigs to 5.15% and 3.3% at 1 μm (n = 6); 21.1% and 20.8% at 5 μm (n = 8); 58.4% and 8.8% at 10 μm (n = 11); 72.7% and 60% at 50 μm (n = 5).

CONCLUSIONS

A significant reduction in contractions but persistence of slow waves suggests imatinib mesylate may affect the smooth muscle contractile mechanism. Imatinib mesylate also significantly reduced contractions in the prostates of younger guinea pigs more than older ones, which is consistent with the notion that the younger guinea-pig prostate is more reliant on the tyrosine-dependent pacemaker ability of interstitial cells of Cajal-like prostatic interstitial cells.

Analysis of erectile responses to imatinib in the rat

OBJECTIVE

To investigate the erectile and cardiovascular responses to the tyrosine kinase inhibitor imatinib in the rat.

MATERIALS AND METHODS

The effect of intracavernosal injection of imatinib on the intracavernosal pressure (ICP), ICP/mean arterial pressure (MAP) ratio, area under the curve, and duration of the increase in ICP and the effect of intravenous injection of imatinib on the MAP, cardiac output, and total peripheral resistance were investigated. The effect of the nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester on the responses to imatinib was investigated.

RESULTS

Intracavernosal injection of imatinib produced significant dose-related increases in the ICP, ICP/MAP ratio, area under the curve, and duration of the increase in ICP and decreases in the MAP. The erectile responses to imatinib were rapid in onset and short in duration. The erectile responses to imatinib were not significantly altered by NG-nitro-L-arginine methyl ester or cavernosal nerve crush injury, and imatinib was significantly less potent than the nitric oxide donor sodium nitroprusside in inducing erection. Intravenous injection of imatinib produced significant dose-related decreases in the MAP without significantly changing the cardiac output, and imatinib was significantly less potent than sodium nitroprusside in decreasing the MAP. Systemic vascular resistance was decreased in a significant dose-related manner, and the vasodilator responses to imatinib were not altered by NG-nitro-L-arginine methyl ester.

CONCLUSION

The present results have indicated that imatinib has significant erectile and systemic vasodilator activity in the rat that is not dependent on nitric oxide release. Another tyrosine kinase inhibitor, nilotinib, also increased the ICP and decreased the MAP in the rat. These data suggest that tyrosine kinases might play a constitutive role in maintaining penile tumescence and the baseline vasoconstrictor tone in the peripheral vascular bed.

The effects of Glivec on the urinary bladder excitation of rats with suprasacral or sacral spinal cord transection

BACKGROUND

To investigate the effects of the c-kit blocker imatinib mesylate (Glivec) on the bladders of animals with suprasacral cord injury (SSCI) and sacral cord injury (SCI).

MATERIALS AND METHODS

We randomized 60 female Sprague-Dawley rats into control, sham, SSCI (T8/9 transection), and SCI (S1-3 transection) groups. Six weeks later, we evaluated the effects of stepwise Glivec administrations on urinary bladder contraction using cystometry and the detrusor strip stretch-test. We investigated spontaneous calcium transients of kit-positive interstitial cells of Cajal (ICCs) with the preloaded Ca(2+) indicator fluo-3AM. The expression levels of c-kit and the number of ICCs in those bladders were determined using Western blot and fluorescence staining analyses, respectively.

RESULTS

Bladder capacity and compliance were decreased in SSCI bladders and increased in SCI bladders (P<0.05). The amplitude and frequency of spontaneous contractions of detrusor strips, the frequency and relative fluorescence intensity of the spontaneous Ca(2+) waves, and c-kit expression in the bladder were significantly increased in the SSCI group and decreased in the SCI group compared with the control and sham groups (P<0.05). The dose-dependent effects of Glivec also confirmed consistent functional variations in bladder activity.

CONCLUSIONS

The expressions and effects of Glivec were enhanced in SSCI bladders and inhibited in SCI bladders, which may indicate potential roles of ICCs for the c-kit signaling pathway in the pathogenesis of SSCI and SCI bladder.

Bladder interstitial cells: an updated review of current knowledge

The field of bladder research has been energized by the study of novel interstitial cells (IC) over the last decade. Several subgroups of IC are located within the bladder wall and make structural interactions with nerves and smooth muscle, indicating integration with intercellular communication and key physiological functions. Significant progress has been made in the study of bladder ICs' cellular markers, ion channels and receptor expression, electrical and calcium signalling, yet their specific functions in normal bladder filling and emptying remain elusive. There is increasing evidence that the distribution of IC is altered in bladder pathophysiologies suggesting that changes in IC may be linked with the development of bladder dysfunction. This article summarizes the current state of the art of our knowledge of IC in normal bladder and reviews the literature on IC in dysfunctional bladder.

Platelet-derived growth factor receptor-α cells in mouse urinary bladder: a new class of interstitial cells

Specific classes of interstitial cells exist in visceral organs and have been implicated in several physiological functions including pacemaking and mediators in neurotransmission. In the bladder, Kit(+) interstitial cells have been reported to exist and have been suggested to be neuromodulators. More recently a second interstitial cell, which is identified using antibodies against platelet-derived growth factor receptor-α (PDGFR-α) has been described in the gastrointestinal (GI) tract and has been implicated in enteric motor neurotransmission. In this study, we examined the distribution of PDGFR-α(+) cells in the murine urinary bladder and the relation that these cells may have with nerve fibres and smooth muscle cells. Platelet-derived growth factor receptor-α(+) cells had a spindle shape or stellate morphology and often possessed multiple processes that contacted one another forming a loose network. These cells were distributed throughout the bladder wall, being present in the lamina propria as well as throughout the muscularis of the detrusor. These cells surrounded and were located between smooth muscle bundles and often came into close morphological association with intramural nerve fibres. These data describe a new class of interstitial cells that express a specific receptor within the bladder wall and provide morphological evidence for a possible neuromodulatory role in bladder function.

Complex effects of imatinib on spontaneous and oxytocin-induced contractions in human non-pregnant myometrium

Human myometrium includes two important cell populations involved in its contractility: smooth muscle fibers and interstitial cells. The pacemaking mechanism is not yet identified, but it is possible that myometrial smooth muscle cells contract in response to a signal generated by c-kit positive interstitial cells. The aim of this study was to investigate the effects of imatinib as a c-kit receptor antagonist on the spontaneous or oxytocin (OT) induced contractions of human non-pregnant myometrium in vitro. Myometrial strips were obtained from non-pregnant women (reproductive age) undergoing hysterectomy for benign indications. The strips were suspended in organ baths for recording of isometric tension. Imatinib effects were assessed on spontaneous contraction and after preexposure to OT.Direct exposure of myometrial strips to imatinib inhibits both amplitude and frequency of contractions (80-320 μM) in a dose dependent manner. Amplitude reverted back to 90% of the baseline amplitude by consequent addition of imatinib (until 480 μM). Total inhibition of myometrial contraction was obtained after addition of OT 60 nM. If myometrium was pre-exposed to OT (320 nM), imatinib 80-160 μm increased amplitude, while decreasing frequency. These data provide evidence that telocytes may be involved as modulators of the spontaneous contractions of the non-pregnant human uterus, via a tyrosine-kinase independent signaling pathway.

Roles of stem cell factor on loss of interstitial cells of Cajal in bladder of diabetic rats

OBJECTIVE

To explore the roles of stem cell factor (SCF) on the loss of interstitial cells (ICCs) in the bladder of diabetic rats, which have not been investigated.

METHODS

The rats were assigned to 3 groups: normal control rats, diabetic rats, and SCF-treated diabetic rats. The diabetic rat model was created using a streptozotocin (60 mg/kg) intraperitoneal injection. The SCF and c-kit levels in bladder tissue were determined using reverse transcriptase-polymerase chain reaction and Western blot analysis. The quantity of ICCs as represented by c-kit-positive cells was examined by image analysis of immunofluorescence staining.

RESULTS

Compared with the control rats, the diabetic rats exhibited a significant decrease in the SCF levels and c-kit expression and number of ICCs in the bladder tissues. All these impaired parameters were effectively restored to the control level after exogenous SCF treatment.

CONCLUSION

These findings suggest that the loss of ICCs in the bladder tissue of diabetic rats can be attributed to a deficiency in endogenous SCF. The beneficial effect of exogenous SCF on diabetic depletion of ICCs could provide a theoretical rationale for the use of SCF as a potential therapeutic drug in treating patients with diabetes-related voiding dysfunction.

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

AIMS

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Role of KIT-Positive Interstitial Cells of Cajal in the Urinary Bladder and Possible Therapeutic Target for Overactive Bladder

In the gastrointestinal tract, interstitial cells of Cajal (ICCs) act as pacemaker cells to generate slow wave activity. Interstitial cells that resemble ICCs in the gastrointestinal tract have been identified by their morphological characteristics in the bladder. KIT is used as an identification marker of ICCs. ICCs in the bladder may be involved in signal transmission between smooth muscle bundles, from efferent nerves to smooth muscles, and from the urothelium to afferent nerves. Recent research has suggested that not only the disturbance of spontaneous contractility caused by altered detrusor ICC signal transduction between nerves and smooth muscle cells but also the disturbance of signal transduction between urothelial cells and sensory nerves via suburothelial ICC may induce overactive bladder (OAB). Recent reports have suggested that KIT is not only a detection marker of these cells, but also may play a crucial role in the control of bladder function. Research into the effect of a c-kit receptor inhibitor, imatinib mesylate, on bladder function implies that KIT-positive ICCs may be therapeutic target cells to reduce bladder overactivity and that the blockage of c-kit receptor may offer a new therapeutic strategy for OAB treatment, although further study will be needed.

The role of c-kit-positive interstitial cells in mediating phasic contractions of bladder strips from streptozotocin-induced diabetic rats

OBJECTIVE

• To investigate the role of c-kit-positive interstitial cells (ICCs) in mediating muscarinic receptor-induced phasic contractions of isolated bladder strips from streptozotocin(STZ)-induced diabetic rats and to confirm the expression and location of ICCs in the rat bladder.

MATERIALS AND METHODS

• Bladders were removed from STZ-induced diabetic rats at 1, 4 and 12 weeks after induction of diabetes and from age-matched controls. • To investigate the functional role of ICCs in mediating phasic contractions, bladder strips were isolated from control and diabetic rats and mounted in tissue baths. • Strips were stimulated with low concentrations of the muscarinic receptor agonist carbachol (CCH; 0.1 µm) to induce phasic contractions and the effect of increasing concentrations (1-50 µm) of imatinib (Glivec® or Gleevec®, formerly STI571), a c-kit tyrosine kinase inhibitor, was then investigated. • For molecular studies, to detect expression of the c-kit tyrosine kinase receptor (c-kit), total cellular RNA was extracted from rat bladders and reverse-transcribed to obtain complementary DNA (cDNA). • Reverse transcription-polymerase chain reaction (RT-PCR) was then performed using primers specific to the c-kit sequence and amplified products separated by agarose gel electrophoresis. • Amplified PCR products were excised from the gel, sequenced and compared with the known c-kit sequence to confirm their identity. • For immunohistochemical detection, whole mount preparations of control rat bladders were fixed in acetone and labelled using antibodies directed to the ICC marker c-kit.

RESULTS

• In functional studies, CCH induced phasic contractions in bladder strips from control and diabetic rats. Bladder strips from 1-week diabetic rats showed CCH-induced phasic contractions, which were greater in amplitude, but had lower frequency, than the controls, whilst no such differences were apparent at later time points of diabetes. • Imatinib decreased the amplitude and the frequency of the CCH-induced phasic contractions in both control and diabetic tissues in a concentration-dependent manner, although in diabetic tissues this effect was only seen at the higher concentrations of imatinib. RT-PCR of bladder cDNA yielded a single amplicon of 480 bp. • The sequence of this amplicon showed a 98% homology with the published c-kit sequence, thus confirming c-kit mRNA expression in both control and 1-week diabetic rat bladder. • Expression of c-kit protein was also detected in a network of cells on the edge of and between smooth muscle bundles of control rat bladders by positive immunoreactivity to c-kit specific antibodies.

CONCLUSION

• These data show the presence of c-kit-positive ICCs in rat urinary bladder and their importance in mediating muscarinic receptor-induced phasic contractions of bladder strips from control and diabetic rats. The role of these ICCs does not seem to be significantly altered by the diabetic state.

Effects of imatinib mesylate in interstitial cells of Cajal from murine small intestine

The interstitial cells of Cajal (ICCs) are pacemakers in the gastrointestinal tract. The possibility of whether imatinib mesylate, a Kit receptor tyrosine kinase inhibitor, modulates pacemaker activities in the ICC was examined using the whole cell patch clamp technique. Imatinib decreased the amplitude of pacemaker potentials in a dose-dependent manner in current-clamp mode. Because the effects of imatinib on pacemaker potentials were the same as those of pinacidil, we examined the effect of glibenclamide on ICC exposed to imatinib. The effects of imatinib on pacemaker potentials were blocked by glibenclamide. To see whether the production of prostaglandins (PGs) is involved in the inhibitory effect of imatinib on pacemaker potentials, we tested the effects of naproxen (a non-selective cyclooxygenase inhibitor) and AH6809 (a prostaglandin EP1 and EP2 receptor antagonist). Naproxen and AH6809 blocked the inhibitory effects of imatinib on ICC. Butaprost (an EP2 receptor agonist) showed the actions on pacemaker potentials in the same manner as imatinib. However, SC 19220 (an EP1 receptor antagonist) has no effects. To investigate the involvement of cAMP and protein kinase A (PKA) in the effects of imatinib on ICC, SQ 22536 (an inhibitor of adenylate cyclase) and mPKAI (an inhibitor of myristoylated PKA) were used. Both SQ-22536 and mPKAI blocked the imatinib-mediated inhibition of pacemaker potentials. However, the protein kinase C (PKC) inhibitors did not block the imatinib-mediated inhibition of pacemaker potentials. These results indicate that imatinib inhibits the pacemaker potentials of ICC by activating ATP-sensitive K(+) channels and PKA-dependent, PKC-independent manner.

Interstitial cells of Cajal in the urinary tract

The study of novel interstitial cells in the tissues of the urinary tract has defined advances in the field in the last decade. These intriguing cells belong to the same family as the better known interstitial cells of Cajal (ICC) of the gastrointestinal tract, and their discovery has been interpreted to suggest that pacemaker cells may be present in the urinary tract, driving the spontaneous or myogenic activity of the neighboring smooth muscle. This scenario may be true for the urethra where ICC have been described as "loose pacemakers" providing multiple, random inputs to modulate urethral smooth muscle activity. However, there is a paucity of direct evidence available to support this hypothesis in the bladder (where the smooth muscle cells are spontaneously active) or the renal pelvis (where atypical smooth muscle cells are the pacemakers), and it now seems more likely that urinary tract ICC act as modulators of smooth muscle activity.Interestingly, the literature suggests that the role of urinary tract ICC may be more apparent in pathophysiological conditions such as the overactive bladder. Several reports have indicated that the numbers of ICC present in overactive bladder tissues are greater than those from normal tissues; moreover, the contractility of tissues from overactive bladders in vitro appears to be more sensitive to the Kit antagonist, glivec, than those from normal bladder. Future research on urinary tract ICC in the short to medium term is likely to be dynamic and exciting and will lead to increasing our understanding of the roles of these cells in both normal and dysfunctional bladder.

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.

Attenuation of bladder overactivity in KIT mutant rats

OBJECTIVES

To investigate morphological and physiological findings in the bladder of KIT mutant (WsRCWs/Ws) rats to clarify whether the disturbance of KIT pathways affects bladder activity. To discuss the potential role of KIT-positive interstitial cells of Cajal (ICC)-like cells in the urinary bladder.

MATERIALS AND METHODS

Reverse transcriptase-polymerase chain reaction and western blotting was used to confirm the absence of c-kit mRNA and protein in the bladders of 12-week-old WsRCWs/Ws rats. Light and transmission electron microscopy was used to identify the differences in morphological and ultrastructural characteristics of the bladder between WsRCWs/Ws and wild-type (WsRC+/+) rats. The voiding pattern of WsRCWs/Ws rats and the effects of cyclophosphamide (CYP) and protamine sulphate on bladder function were examined using cystometry.

RESULTS

In WsRC+/+ rats, c-kit mRNA and KIT protein expression were observed in the urinary bladder, while they were not detectable in WsRCWs/Ws rats. Deformation of ICC-like cells with the collapse of the organelle was not observed in the bladders of WsRCWs/Ws rats. Each cystometry variable in WsRCWs/Ws rats was similar to that in WsRC+/+ rats. The reduction in the intercontraction intervals in WsRCWs/Ws rats with chemically (CYP and protamine sulphate) induced cystitis was significantly lower than in WsRC+/+ rats (P < 0.05).

CONCLUSION

Certain voiding disturbances might be associated with impaired KIT signalling in ICC-like cells, therefore, KIT could be a candidate target for medical therapy in the future.

Effects of mechanical stretch on interstitial cells of Cajal in guinea pig bladder

OBJECTIVES

C-kit positive interstitial cells of Cajal (ICCs) play an important role in the regulation of the smooth muscle motility. In this study, we investigated the mechanical sensitivity of ICCs in guinea pig bladder and their possible relationship with detrusor overactivity (DO).

METHODS

Stretch load was performed in vivo in DO models produced by 4 wk of partial bladder outlet obstruction (PBOO). Number and morphology of ICCs were examined using a specific ICC marker, c-kit, immunochemistry staining. The spontaneous and stretch-induced calcium transients (SICT) of ICCs were investigated in cells cultured onto flexible silicone membranes preloaded with the Ca(2+) indicator fluo-4AM in vitro.

RESULTS

C-kit positive ICCs were mainly located along and between bladder smooth muscle bundles. ICCs in DO bladders displayed more lateral branching with mutual connections. The number of c-kit positive bladder ICCs was increased in the DO group compared with the control group (n = 50, P < 0.05). Cultured ICCs from DO bladders showed spontaneous calcium waves with higher frequency and lower amplitude than those from control bladders (n = 15, P < 0.05). Significant SICT were detected in cultured bladder ICCs. SICT generated in ICCs from DO were more likely to transfer to adjacent smooth muscle cells through cell membrane connection than ICCs from control bladders.

CONCLUSIONS

Long-term overload tension following PBOO caused changes in morphology, quantity and spontaneous calcium transients of ICCs in guinea pig bladder. Mechanical sensitivity and interaction with SMC of ICCs may contribute to the mechanosensitive conductances in bladder regulation, and may play a role in the pathogenesis of DO.

Morphological expression of KIT positive interstitial cells of Cajal in human bladder

PURPOSE

We investigated the 3-dimensional morphological arrangement of KIT positive interstitial cells of Cajal in the human bladder and explored their structural interactions with neighboring cells.

MATERIALS AND METHODS

Human bladder biopsy samples were prepared for immunohistochemistry/confocal or transmission electron microscopy.

RESULTS

Whole mount, flat sheet preparations labeled with anti-KIT (Merck, Darmstadt, Germany) contained several immunopositive interstitial cell of Cajal populations. A network of stellate interstitial cells of Cajal in the lamina propria made structural connections with a cholinergic nerve plexus. Vimentin positive cells of several morphologies were present in the lamina propria, presumably including fibroblasts, interstitial cells of Cajal and other cells of mesenchymal origin. Microvessels were abundant in this region and branched, elongated KIT positive interstitial cells of Cajal were found discretely along the vessel axis with each perivascular interstitial cell of Cajal associated with at least 6 vascular smooth muscle cells. Detrusor interstitial cells of Cajal were spindle-shaped, branched cells tracking the smooth muscle bundles, closely associated with smooth muscle cells and vesicular acetylcholine transferase nerves. Rounded, nonbranched KIT positive cells were more numerous in the lamina propria than in the detrusor and were immunopositive for anti-mast cell tryptase. Transmission electron microscopy revealed cells with the ultrastructural characteristics of interstitial cells of Cajal throughout the human bladder wall.

CONCLUSIONS

The human bladder contains a network of KIT positive interstitial cells of Cajal in the lamina propria, which make frequent connections with a cholinergic nerve plexus. Novel perivascular interstitial cells of Cajal were discovered close to vascular smooth muscle cells, suggesting interstitial cells of Cajal-vascular coupling in the bladder. KIT positive detrusor interstitial cells of Cajal tracked smooth muscle bundles and were associated with nerves, perhaps showing a functional tri-unit controlling bladder contractility.

Detrusor myocyte activity and afferent signaling

AIMS

To discuss (1) mechanisms involved in the generation and control of myocyte contractions and consequent afferent nerve activity and (2) these mechanisms as targets for drugs aimed for treatment of overactive bladder (OAB) symptoms and detrusor overactivity (DO).

METHODS

Literature review of myocyte activation, bladder afferent nerves, mediators in the bladder, and translational aspects of the findings.

RESULTS

During bladder filling, there is normally no parasympathetic outflow from the spinal cord. Despite this, the bladder develops tone during filling and also exhibits non-synchronized local contractions and relaxations that are caused by a basal myogenic mechanical activity that may be reinforced by release of, for example, acetylcholine from non-neuronal and/or neuronal sources or local mediators, such as prostaglandins and endothelins. It is suggested that these spontaneous contractions are able to generate activity in afferent nerves ("afferent noise") that may contribute to DO and OAB.

CONCLUSIONS

Spontaneous bladder myocyte contractions and factors that are able to modulate them, as well as the consequent afferent nerve activity, may be targets for drugs meant for treatment of OAB/DO.

Altered cytosolic Ca2+ dynamics in cultured Guinea pig cardiomyocytes as an in vitro model to identify potential cardiotoxicants

Altered intracellular calcium (Ca(i)(2+)) handling by cardiomyocytes has been implicated in drug-induced cardiomyopathy and arrhythmogenesis. To explore whether such alterations predict cardiotoxicity, Ca(i)(2+) imaging was conducted in cultured, spontaneously contracting Guinea pig cardiomyocytes to characterize the effects of 13 cardiotoxicants and 2 safe drugs. All cardiotoxicants perturbed Ca(i)(2+) at therapeutically relevant concentrations. The cytotoxic chemotherapeutics doxorubicin and epirubicin, known to cause cardiomyopathy, preferentially reduced Ca(i)(2+) transient amplitude and sarcoplasmic reticulum (SR) Ca(2+) content, whereas Torsade de Pointes (TdP) inducers and potent hERG channel blockers (amiodarone, cisapride, dofetilide, E-4031 and terfenadine) predominately suppressed diastolic Ca(i)(2+) and contraction rate, and prolonged Ca(i)(2+) transient duration. The molecularly targeted cancer therapeutics, sunitinib and imatinib, exhibited profound effects on Ca(i)(2+), combining effects of cytotoxic chemotherapeutics, TdP inducers and potent hERG channel blockers. TdP inducers lacking direct hERG inhibition, ouabain and pentamidine, significantly elevated Ca(i)(2+) transient amplitude and SR Ca(2+) content while aconitine primarily accelerated automaticity and elevated diastolic Ca(i)(2+) similar to ouabain. Finally, amoxicillin and aspirin did not exert any significant effects on Ca(i)(2+) at concentrations up to 100 microM. These results suggest that detecting altered Ca(i)(2+) handling in cultured cardiomyocytes may be used as an in vitro model for early cardiac drug safety assessment.

Expression of C-kit messenger ribonucleic acid and C-kit protein in the gallbladders in guinea pigs of high cholesterol diet

The c-kit protooncogene receptor and its ligand-stem cell factor regulating the proliferation and survival of interstitial cells of Cajal (ICCs) have been described. The aim of this study was to determine the expression of c-kit mRNA and c-kit protein in the gallbladders in guinea pigs of high cholesterol diet (HCD). The gallbladder samples from 16 guinea pigs of HCD and from 16 guinea pigs of standard diet (StD) were used for this study. Expression of c-kit mRNA was detected by reverse transcription polymerase chain reaction (RT-PCR), and expression of c-kit protein was detected by Western blot analysis. Serum total cholesterol (TC) (39 +/- 6 vs. 109 +/- 20 mg/dl), low density lipoprotein (LDL) cholesterol (24 +/- 4 vs. 71 +/- 10 mg/dl), high density lipoprotein (HDL) cholesterol (2.4 +/- 0.4 vs. 7.0 +/- 1.6 mg/dl), and triglyceride (TG) (58 +/- 8 vs. 118 +/- 23 mg/dl) concentrations were significantly higher in the HCD group than in the StD group of guinea pigs (P < 0.001, respectively). Decreased expression of c-kit mRNA was demonstrated in the HCD group compared with the StD group. The ratio of c-kit mRNA and GAPDH was 0.56 +/- 0.09 in controls and 0.50 +/- 0.07 in the HCD group (P = 0.033). C-kit protein expression significantly declined in the HCD group. The mean value of optical density was 129 +/- 25 in the StD group and 103 +/- 19 in the HCD group (P = 0.0009). The data indicate that the expression of c-kit mRNA and c-kit protein significantly decreased in the gallbladders in guinea pigs of HCD.

Altered distribution of interstitial cells in the guinea pig bladder following bladder outlet obstruction

AIMS

We investigated the effects of bladder outlet obstruction (BOO) on the distribution of interstitial cells (ICs) in the guinea-pig bladder.

METHODS

Bladder overactivity of BOO animals was validated with urodynamic studies. Immunohistochemical analyses for Kit and vimentin as markers for ICs were performed on both BOO and control bladders. Morphological and functional properties of detrusor smooth muscle (DSM) were examined with alpha-smooth muscle actin staining and intracellular recording, respectively. Electron microscopy was also carried out to characterize ultrastructural morphology of ICs.

RESULTS

Two weeks after surgery, BOO animals showed an increased voiding frequency and a reduced voiding volume. Filling cystometry demonstrated a frequent incidence of non-voiding contractions, a reduced interval between voiding contractions and an increased voiding pressure in BOO bladders. In BOO bladders, the thickness of suburothelial and subserosal connective tissue layers was increased, whilst that of detrusor smooth muscle (DSM) layer was less affected. Population of Kit or vimentin immunoreactive ICs was increased in subserosal layers, and their distribution was altered in suburotherial layer in BOO bladders. Neither alpha-actin immunoreactivity nor spontaneous electrical activity of DSM was altered in BOO bladders. ICs were characterized by their numerous mitochondria and caveolae, and had a close contact with each other and with neighboring DSM or nerves.

CONCLUSIONS

These results demonstrated the increased population of ICs in the BOO guinea-pig model for the first time, and suggest that the altered distribution of ICs may contribute to the pathophysiology of bladder overactivity.

Distribution of the interstitial Cajal-like cells in the gallbladder and extrahepatic biliary duct of the guinea-pig

It has been suggested that interstitial Cajal-like cells (ICLC) may be involved in the spontaneous rhythmic electrical activities of the extrahepatic bile duct system. The present study investigated the distribution and characteristics of ICLC, which are immunopositive for CD117/ Kit receptor tyrosine kinase, using immunohistochemistry employing a monoclonal antibody raised against CD117/Kit on whole-mount preparations. The Kit-positive ICLC were examined using confocal laser scanning microscopy or fluorescence microscopy. ICLC, immunoreactive for Kit, were pleiomorphic and/or spindle-shaped cells with a few bipolar processes and distributed in the smooth muscle layers of the gallbladder and bile duct system. They were scattered in the hepatic duct, cystic duct and gallbladder as well as in the upper part of the common bile duct. The ICLC gradually increased in number and formed a completed cellular network in the lower part of the common bile duct and ampulla. The numbers of ICLC in the ampulla were similar to that of the duodenum and significantly much greater in number than in the gallbladder and bile ducts. The density of the ICLC in the common bile duct was significantly higher than that of other bile ducts. Our results suggested that the ICLC might contribute to the regulation of the spontaneous rhythmic contraction and development of motility disorders of the bile duct system.

Modulation of bladder myofibroblast activity: implications for bladder function

Bladder suburothelial myofibroblasts may modulate both sensory responses from the bladder wall and spontaneous activity. This study aimed to characterize further these cells in their response to exogenous agents implicated in mediating the above activity. Detrusor strips, with or without mucosa, and isolated suburothelial myofibroblasts were prepared from guinea pig bladders. Isometric tension, intracellular Ca²⁺, and membrane current were recorded. Cell pairs were formed by pushing two cells together. Tension, intracellular Ca²⁺, and membrane potential were also recorded from bladder sheets using normal or spinal cord-transected (SCT) rats. Spontaneous contractions were greater in detrusor strips with an intact mucosa and were augmented by 10 μM UTP. ATP, UTP, or reduced extracellular pH elicited Ca²⁺ transients and inward currents (E_rev −30 mV) in isolated cells. Capsaicin (5–30 μM) reduced membrane current (37 ± 12% of control) with minor effects on Ca²⁺ transients: sodium nitroprusside reduced membrane currents (40 ± 21% of control). Cell pair formation, without an increase in cell capacitance, augmented ATP and pH responses (180 ± 58% of control) and reduced the threshold to ATP and acidosis. Glivec (20–50 μM) reversibly blocked the augmentation and also reduced spontaneous activity in bladder sheets from SCT, but not normal, rats. Glivec also disrupted the spread of Ca²⁺ waves in SCT sheets, generating patterns similar to normal bladders. Suburothelial myofibroblasts respond to exogenous agents implicated in modulating bladder sensory responses; responses augmented by physical intercellular contact. The action of glivec and its selective suppression of spontaneous activity in SCT rats identifies a possible pathway to attenuate bladder overactivity.

Effects of imatinib mesylate on spontaneous electrical and mechanical activity in smooth muscle of the guinea-pig stomach

BACKGROUND AND PURPOSE

Effects of imatinib mesylate, a Kit receptor tyrosine kinase inhibitor, on spontaneous activity of interstitial cells of Cajal (ICC) and smooth muscles in the stomach were investigated.

EXPERIMENTAL APPROACH

Effects of imatinib on spontaneous electrical and mechanical activity were investigated by measuring changes in the membrane potential and tension recorded from smooth muscles of the guinea-pig stomach. Its effects on spontaneous changes in intracellular concentration of Ca(2+) ([Ca(2+)](i)) (Ca(2+) transients) were also examined in fura-2-loaded preparations.

KEY RESULTS

Imatinib (1-10 microM) suppressed spontaneous contractions and Ca(2+) transients. Simultaneous recordings of electrical and mechanical activity demonstrated that imatinib (1 microM) reduced the amplitude of spontaneous contractions without suppressing corresponding slow waves. In the presence of nifedipine (1 microM), imatinib (10 microM) reduced the duration of slow waves and follower potentials in the antrum and accelerated their generation, but had little affect on their amplitude. In contrast, imatinib reduced the amplitude of antral slow potentials and slow waves in the corpus.

CONCLUSIONS AND IMPLICATIONS

Imatinib may suppress spontaneous contractions of gastric smooth muscles by inhibiting pathways that increase [Ca(2+)](i) in smooth muscles rather than by specifically inhibiting the activity of ICC. A high concentration of imatinib (10 microM) reduced the duration of slow waves or follower potentials in the antrum, which reflect activity of ICC distributed in the myenteric layers (ICC-MY), and suppressed antral slow potentials or corporal slow waves, which reflect activity of ICC within the muscle bundles (ICC-IM), presumably by inhibiting intracellular Ca(2+) handling.

Therapeutic receptor targets for lower urinary tract dysfunction

The functions of the lower urinary tract, to store and periodically release urine, are dependent on the activity of smooth and striated muscles in the bladder, urethra, and external urethral sphincter. During urine storage, the outlet is closed, and the bladder smooth muscle is quiescent. When bladder volume reaches the micturition threshold, activation of a micturition center in the dorsolateral pons (the pontine micturition center) induces a bladder contraction and a reciprocal relaxation of the urethra, leading to bladder emptying. During voiding, sacral parasympathetic (pelvic) nerves provide an excitatory input (cholinergic and purinergic) to the bladder and inhibitory input (nitrergic) to the urethra. These peripheral systems are integrated by excitatory and inhibitory regulation at the levels of the spinal cord and the brain. Injury or diseases of the nervous system, as well as drugs and disorders of the peripheral organs, can produce lower urinary tract dysfunction. In the overactive bladder (OAB) condition, therapeutic targets for facilitation of urine storage can be found at the levels of the urothelium, detrusor muscles, autonomic and afferent pathways, spinal cord, and brain. There is increasing evidence showing that the urothelium has specialized sensory and signaling properties including: (1) expression of nicotinic, muscarinic, tachykinin, adrenergic, bradykinin, and transient receptor potential (TRP) receptors, (2) close physical association with afferent nerves, and (3) ability to release chemical molecules such as adenosine triphosphate (ATP), acetylcholine, and nitric oxide. Increased expression and/or sensitivity of these urothelial-sensory molecules that lead to afferent sensitization have been documented as possible pathogenesis of OAB. Targeting afferent pathways and/or bladder smooth muscles by modulating activity of ligand receptors (e.g., neurokinin, ATP, or beta3-adrenergic receptors) and ion channels (e.g., TRPV1 or K) could be effective to suppress OAB. In the stress urinary incontinence condition, pharmacotherapies targeting the neurally mediated urethral continence reflex during stress conditions such as sneezing or coughing could be effective for increasing the outlet resistance. Therapeutic targets include adrenergic and serotonergic receptors in the spinal cord as well as adrenergic receptors at the urethral sphincter, which can enhance urethral reflex activity during stress conditions and increase baseline urethral pressure, respectively.

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

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

Interstitial Cajal-like cells in human uterus and fallopian tube

Recently, parallels have been drawn between enteric interstitial cells of Cajal (ICC) and similar cells outside the gut-interstitial Cajal-like cells (ICLC). This article reviews our laboratory findings on ICLC in the female reproductive tract. Since the morphology and function of ICLC are still a subject of debate, our purpose was to investigate whether ICLC are present in the fallopian tube and/or uterus, and if they share ultrastructural and immunohistochemical (IHC) features and/or functional roles. We studied ICLC presence in the human fallopian tube and myometrium primarily by light microscopy, and then by transmission electron microscopy (TEM), in tissue samples and at a single cell level. Taking advantage of our ICLC studies of several organs (pancreas, mammary gland, myocardium), we assembled a set of criteria, derived from ultrastructural features of ICLC, called "platinum standard." Besides the putative pacemaker function, ICLC might have other physiological roles, depending on tissue type (e.g., intercellular signaling, immune surveillance, steroid sensors). Consequently, there is a great urge for a conceptual framework that could allow a better understanding, from a functional point of view, and more so, as the ICLC processes are the longest cellular prolongations (except neurons).