Interstitial cells of Cajal in the urethra

The urethra in continence and sensation: Neural aspects of urethral function

AIMS

Traditionally, the urethra has been considered a mere conduit to guide urine from the bladder to the external side of the body. Building evidence indicates that the urethra may directly influence bladder function via mechanisms restricted to the lower urinary tract (LUT).

METHODS

Here, we discuss the tissue arrangement of the urethra and addressed the contribution of new paraneuronal cells to LUT function. We also briefly reviewed two frequent LUT pathologies associated with urethral dysfunction.

RESULTS

Continence depends on an intact and functional urethral sphincter, composed of smooth, and striated muscle fibers and regulated by somatic and autonomic fibers. Recent studies suggest the existence of an urethro-vesical reflex that also contributes to normal LUT function. Indeed, the urethral lumen is lined by a specialized epithelium, the urothelium, in the proximal urethra. In this region, recent evidence demonstrates the presence of specific paraneuronal cells, expressing the neurotransmitters acetylcholine and serotonin. These cells are in close proximity of nerve fibers coursing in the lamina propria and are able to release neurotransmitters and rapidly induce detrusor contractions, supporting the existence of an urethro-vesical crosstalk.

CONCLUSION

The mechanism underlying the fast communication between the urethra and thebladder are beginning to be understood and should involve the interaction between specificepithelial cells and fibres innervating the urethral wall. It is likely that this reflex should bealtered in pathological conditions, becoming an attractive therapeutic target.

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.

A novel intramuscular Interstitial Cell of Cajal is a candidate for generating pacemaker activity in the mouse internal anal sphincter

The internal anal sphincter (IAS) generates phasic contractions and tone. Slow waves (SWs) produced by interstitial cells of Cajal (ICC) underlie phasic contractions in other gastrointestinal regions. SWs are also present in the IAS where only intramuscular ICC (ICC-IM) are found, however the evidence linking ICC-IM to SWs is limited. This study examined the possible relationship between ICC-IM and SWs by recording Ca2+ transients in mice expressing a genetically-encoded Ca2+-indicator in ICC (Kit-Cre-GCaMP6f). A role for L-type Ca2+ channels (CavL) and anoctamin 1 (ANO1) was tested since each is essential for SW and tone generation. Two distinct ICC-IM populations were identified. Type I cells (36% of total) displayed localised asynchronous Ca2+ transients not dependent on CavL or ANO1; properties typical of ICC-IM mediating neural responses in other gastrointestinal regions. A second novel sub-type, i.e., Type II cells (64% of total) generated rhythmic, global Ca2+ transients at the SW frequency that were synchronised with neighbouring Type II cells and were abolished following blockade of either CavL or ANO1. Thus, the spatiotemporal characteristics of Type II cells and their dependence upon CavL and ANO1 all suggest that these cells are viable candidates for the generation of SWs and tone in the IAS.

Contribution of Cav1.2 Ca2+ channels and store-operated Ca2+ entry to pig urethral smooth muscle contraction

Urethral smooth muscle (USM) generates tone to prevent urine leakage from the bladder during filling. USM tone has been thought to be a voltage-dependent process, relying on Ca²⁺ influx via voltage-dependent Ca²⁺ channels in USM cells, modulated by the activation of Ca²⁺-activated Cl^- channels encoded by Ano1. However, recent findings in the mouse have suggested that USM tone is voltage independent, relying on Ca²⁺ influx through Orai channels via store-operated Ca²⁺ entry (SOCE). We explored if this pathway also occurred in the pig using isometric tension recordings of USM tone. Pig USM strips generated myogenic tone, which was nearly abolished by the Ca_v1.2 channel antagonist nifedipine and the ATP-dependent K⁺ channel agonist pinacidil. Pig USM tone was reduced by the Orai channel blocker GSK-7975A. Electrical field stimulation (EFS) led to phentolamine-sensitive contractions of USM strips. Contractions of pig USM were also induced by phenylephrine. Phenylephrine-evoked and EFS-evoked contractions of pig USM were reduced by ~50-75% by nifedipine and ~30% by GSK-7975A. Inhibition of Ano1 channels had no effect on tone or EFS-evoked contractions of pig USM. In conclusion, unlike the mouse, pig USM exhibited voltage-dependent tone and agonist/EFS-evoked contractions. Whereas SOCE plays a role in generating tone and agonist/neural-evoked contractions in both species, this dominates in the mouse. Tone and agonist/EFS-evoked contractions of pig USM are the result of Ca²⁺ influx primarily through Ca_v1.2 channels, and no evidence was found supporting a role of Ano1 channels in modulating these mechanisms.

Neutrophils injure gallbladder interstitial Cajal-like cells in a guinea pig model of acute cholecystitis

Acute cholecystitis is a common disease with gallbladder dysmotility. Disease pathogenesis involves immune cell infiltration as well as changes in gallbladder interstitial Cajal-like cells (ICLCs). However, it remains unclear if or how the immune cells affect ICLC morphology, density, distribution, and function in gallbladder tissue during acute cholecystitis. In this study, we explored the acute cholecystitis-related alterations in gallbladder ICLCs in a guinea pig model, focusing on the effects of neighboring neutrophils. Adult guinea pigs were randomly divided into four groups (control, 24 hr common bile duct ligation [CBDL], 48-hr CBDL, and antipolymorphonuclear neutrophil [PMN] treated) and analyzed using methylene blue staining and immunofluorescence. Gallbladder contractility was also monitored. To culture gallbladder ICLCs, collagenase digestion was performed on tissue from 10- to 15-day-old guinea pigs. Neutrophils isolated from the peripheral blood of experimental animals 48-hr postsurgery were also cocultured with the gallbladder ICLCs. Intracellular calcium was detected with Fluo-4 AM dye. Our results showed that gallbladder ICLC density significantly declined during acute cholecystitis and was accompanied by shortening of the cellular processes and damage to their network-like structure. However, pretreatment with anti-PMN partially prevented these changes. Gallbladder contraction was also significantly decreased during acute cholecystitis, and this appeared to be mediated by the neutrophils. Moreover, ICLCs cocultured with neutrophils also had shortened and reduced processes and impaired network-like structure formation. Intracellular calcium transient was less sensitive to contraction agonists and inhibitors when cocultured with neutrophils. Taken together, neutrophils greatly affect gallbladder ICLCs and dysmotility during acute cholecystitis.

Telocytes: New Players in Gallstone Disease

Cholesterol gallstone disease is highly prevalent in Western countries, particularly in women and some specific ethnic groups. The mechanisms behind the formation of gallstones are not clearly understood, but gallbladder dysmotility seems to be a key factor that triggers the precipitation of cholesterol microcrystals from supersaturated lithogenic bile.Given that newly described interstitial cells, telocytes, are present in the gallbladder and they are located in close vicinity of smooth muscle cell and neural fibers possibly interfering with gallbladder motility or contractility, authors are trying to summarize the current knowledge on the role of telocytes with respect to disturbed gallbladder function in gallstone disease.

The Dome Wall of Bladder Acts as a Pacemaker Site in Detrusor Instability in Rats

BACKGROUND The aim of this study was to confirm that the interstitial cells of Cajal (ICCs) in the dome wall of the bladder are pacemaker cells, and that the dome wall of the bladder acts as a pacemaker site in the detrusor instability (DI) rat model. MATERIAL AND METHODS The model of DI in Wistar rats was established and urodynamic studies measuring the bladder volume and pressure were performed. The detrusor excitability was investigated using the amplitude and frequency of phasic contraction of strips. The localization and quantity of ICCs was identified by immunohistochemistry and c-KIT protein expression in the rat bladder. PCR assay and Western blot were used to assess the expression of HCN2 and Cx43. RESULTS The bladder capacity, residual volume, voiding volume, and maximum voiding pressure were significantly increased in the DI group. The contraction frequency and amplitude of the strips from the dome of the bladder in the DI group were higher than the triangle, body, and base parts. Both the concentration of c-KIT positive ICCs cells and expression of the c-KIT protein in the dome wall were higher than in other parts of the bladder. The expression of HCN2 and Cx43 in each part of the DI rat group were obviously higher than each part in the control group. Compared to the body, base, and triangle parts, the expression of HCN2 and Cx43 in the dome wall were obviously higher in the DI group. CONCLUSIONS The quantity of ICCs was higher in the dome wall and the dome wall of bladder acts as a pacemaker site in the DI rat model.

The History of Telocyte Discovery and Understanding

Telocytes (TCs) are identified as a peculiar cell type of interstitial cells in various organs. The typical features of TCs from the other cells are the extending cellular process as telopodes with alternation of podomeres and podoms. Before the year of 2010, TCs were considered as interstitial Cajal-like cells because of the similar morphology and immunohistochemical features with interstitial cells of Cajal which were found more than 100 years ago and considered to be pacemakers for gut motility. Subsequently, it demonstrated that TCs were not Cajal-like cells, and thus the new name "telocyte" was proposed in 2010. With the help of different techniques, e.g., transmission electron microscopy, immunohistochemistry, or omics science, TCs have been detected in various tissues and organs from different species. The pathological role of TCs in different diseases was also studied. According to observation in situ or in vitro, TCs played a vital role in mechanical support, signaling transduction, tissue renewal or repair, immune surveillance, and mechanical sensor via establishing homo- or heterogenous junctions with neighboring cells to form 3D network or release extracellular vesicles to form juxtacrine and paracrine. This review will introduce the origin, distribution, morphology, functions, omics science, methods, and interaction of TCs with other cells and provide a better understanding of the new cell type.

Telocytes in regenerative medicine

Telocytes (TCs) are a distinct type of interstitial cells characterized by a small cell body and extremely long and thin telopodes (Tps). The presence of TCs has been documented in many tissues and organs (go to http://www.telocytes.com). Functionally, TCs form a three-dimensional (3D) interstitial network by homocellular and heterocellular communication and are involved in the maintenance of tissue homeostasis. As important interstitial cells to guide or nurse putative stem and progenitor cells in stem cell niches in a spectrum of tissues and organs, TCs contribute to tissue repair and regeneration. This review focuses on the latest progresses regarding TCs in the repair and regeneration of different tissues and organs, including heart, lung, skeletal muscle, skin, meninges and choroid plexus, eye, liver, uterus and urinary system. By targeting TCs alone or in tandem with stem cells, we might promote regeneration and prevent the evolution to irreversible tissue damage. Exploring pharmacological or non-pharmacological methods to enhance the growth of TCs would be a novel therapeutic strategy besides exogenous transplantation for many diseased disorders.

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.

Mechanisms underlying activation of transient BK current in rabbit urethral smooth muscle cells and its modulation by IP3-generating agonists

We used the perforated patch-clamp technique at 37°C to investigate the mechanisms underlying the activation of a transient large-conductance K(+) (tBK) current in rabbit urethral smooth muscle cells. The tBK current required an elevation of intracellular Ca(2+), resulting from ryanodine receptor (RyR) activation via Ca(2+)-induced Ca(2+) release, triggered by Ca(2+) influx through L-type Ca(2+) (CaV) channels. Carbachol inhibited tBK current by reducing Ca(2+) influx and Ca(2+) release and altered the shape of spike complexes recorded under current-clamp conditions. The tBK currents were blocked by iberiotoxin and penitrem A (300 and 100 nM, respectively) and were also inhibited when external Ca(2+) was removed or the CaV channel inhibitors nifedipine (10 μM) and Cd(2+) (100 μM) were applied. The tBK current was inhibited by caffeine (10 mM), ryanodine (30 μM), and tetracaine (100 μM), suggesting that RyR-mediated Ca(2+) release contributed to the activation of the tBK current. When IP3 receptors (IP3Rs) were blocked with 2-aminoethoxydiphenyl borate (2-APB, 100 μM), the amplitude of the tBK current was not reduced. However, when Ca(2+) release via IP3Rs was evoked with phenylephrine (1 μM) or carbachol (1 μM), the tBK current was inhibited. The effect of carbachol was abolished when IP3Rs were blocked with 2-APB or by inhibition of muscarinic receptors with the M3 receptor antagonist 4-diphenylacetoxy-N-methylpiperidine methiodide (1 μM). Under current-clamp conditions, bursts of action potentials could be evoked with depolarizing current injection. Carbachol reduced the number and amplitude of spikes in each burst, and these effects were reduced in the presence of 2-APB. In the presence of ryanodine, the number and amplitude of spikes were also reduced, and carbachol was without further effect. These data suggest that IP3-generating agonists can modulate the electrical activity of rabbit urethral smooth muscle cells and may contribute to the effects of neurotransmitters on urethral tone.

Identification of telocytes in the upper lamina propria of the human urinary tract

The upper lamina propria (ULP) area of interstitial cells (IC) has been studied extensively in bladder, but is rather unexplored in the rest of the urinary tract. This cell layer is intriguing because of the localization directly underneath the urothelium, the intercellular contacts and the close relationship with nerve endings and capillaries. In this study, we examine the ULP layer of IC in human renal pelvis, ureter and urethra, and we make a comparison with ULP IC in bladder. Tissue was obtained from normal areas in nephrectomy, cystectomy and prostatectomy specimens, and processed for morphology, immunohistochemistry and electron microscopy. A morphological and immunohistochemical phenotype for the ULP IC was assessed and region-dependent differences were looked for. The ULP IC in renal pelvis, ureter and urethra had a similar ultrastructural phenotype, which differed somehow from that of bladder IC, that is, thinner and longer cytoplasmic processes, no peripheral actin filaments and presence of dense core granules and microtubules. Together with their immunohistochemical profile, these features are most compatible with the phenotype of telocytes, a recently discovered group of stromal cells. Based on their global ultrastructural and immunohistochemical phenotype, ULP IC in human bladder should also be classified as telocytes. The most striking immunohistochemical finding was the variable expression of oestrogen receptor (ER) and progesterone receptor (PR). The functional relevance of ULP telocytes in the urinary tract remains to be elucidated, and ER and PR might therefore be promising pharmacological research targets.

Interstitial cells in the primate gastrointestinal tract

Kit immunohistochemistry and confocal reconstructions have provided detailed 3-dimensional images of ICC networks throughout the gastrointestinal (GI) tract. Morphological criteria have been used to establish that different classes of ICC exist within the GI tract and physiological studies have shown that these classes have distinct physiological roles in GI motility. Structural studies have focused predominately on rodent models and less information is available on whether similar classes of ICC exist within the GI tracts of humans or non-human primates. Using Kit immunohistochemistry and confocal imaging, we examined the 3-dimensional structure of ICC throughout the GI tract of cynomolgus monkeys. Whole or flat mounts and cryostat sections were used to examine ICC networks in the lower esophageal sphincter (LES), stomach, small intestine and colon. Anti-histamine antibodies were used to distinguish ICC from mast cells in the lamina propria. Kit labeling identified complex networks of ICC populations throughout the non-human primate GI tract that have structural characteristics similar to that described for ICC populations in rodent models. ICC-MY formed anastomosing networks in the myenteric plexus region. ICC-IM were interposed between smooth muscle cells in the stomach and colon and were concentrated within the deep muscular plexus (ICC-DMP) of the intestine. ICC-SEP were found in septal regions of the antrum that separated circular muscle bundles. Spindle-shaped histamine(+) mast cells were found in the lamina propria throughout the GI tract. Since similar sub-populations of ICC exist within the GI tract of primates and rodents and the use of rodents to study the functional roles of different classes of ICC is warranted.

Bladder outlet physiology in the context of lower urinary tract dysfunction

Physiological function of the bladder outlet is complex and symptomatic consequences can result from outlet dysfunction. Within the outlet, smooth, and skeletal muscles constitute the contractile apparatus, but additional cell types include interstitial cells and neuroendocrine cells, and various transmitters are present in the innervation, raising the possibility of unrecognized functional subtleties. Key outlet functions are; maintained closure for urine storage, increased closure (guarding) during exertion, sustained opening for voiding, transient opening for territorial marking in animals and orthograde male ejaculation. These are co-ordinated by several spinal and higher CNS centers, with overlap of the somatic, sympathetic and parasympathetic nervous systems. During voiding, urethral afferents may be important in maintaining detrusor contraction until completion of bladder emptying. Some of the bladder outlet afferents may be shared with the anal sphincter. Dysfunction of the outlet leads to conditions such as retrograde ejaculation, Fowler's syndrome, and detrusor sphincter dyssynergia. Urethral relaxation during urine storage may lead to urinary urgency, which may be misleadingly labeled as overactive bladder. Research priorities are numerous, including; peripheral cellular integrative physiology, interactions with other pelvic organs, interconnectivity of the CNS centers at all levels of the neuraxis, and standardized animal models of outlet functions such as reflex-driven voiding.

Direct coupling through gap junctions is not involved in urethral neurotransmission

Interstitial cells of Cajal (ICC) are believed to participate in urethral neurotransmission and it was proposed that direct coupling of ICC and smooth muscle cells (SMC) through gap junctions (GJ) is involved, although this still remains unclear. Hence, we investigated the distribution of different connexins (Cx 43, Cx40, and Cx37) in the sheep and rat urethra, as well as their possible role in neurotransmission. Conventional PCR confirmed that three Cxs are expressed in the urethra. Moreover, both Cx43 and Cx37-immunoreactivity (-ir) were present in SMC, ICC, and the urothelium, although Cx37-ir was significantly weaker and Cx40-ir was limited to the endothelium. While these results indicate that GJ intercellular communication could occur between SMC and ICC, neither the contractile (noradrenergic) nor the relaxant (nitrergic) responses of the rat and sheep urethra to electrical field stimulation were significantly modified by two different GJ inhibitors: 18α-glycyrrhetinic acid and a cocktail of Cx mimetic peptides (Cx43Gap 26,Cx37, Cx43Gap 27, andCx40Gap 27). By contrast, contractions induced by high K+were effectively reduced by both blockers, evidence that they effectively inhibit intercellular communication. These results indicate that GJ are not implicated in urethral neurotransmission, although the question of whether ICC modulate neurotransmission through some other mechanism remains to be determined.

Identification of telocytes in the lamina propria of rat duodenum: transmission electron microscopy

Recently the new term 'telocytes' has been proposed for cells formerly known as interstitial Cajal-like cells. In fact, telocytes are not really Cajal-like cells, they being different from all other interstitial cells by the presence of telopodes, which are cell-body prolongations, very thin, extremely long with a moniliform aspect. The identification of these cells is based on ultrastructural criteria. The presence of telocytes in others organs was previously documented. We reported for the first time, an ultrastructural study of telocytes in the lamina propria of rat duodenum. Our findings show that typical telocytes are present in the rat duodenum. Telocytes are located in the lamina propria, immediately below mucosal crypts. Telopodes frequently establish close spatial relationships with immune cells, blood vessels and nerve endings. On the basis of their distribution and morphology, we suggest that these cells may be involved in immune response and in our opinion, it may be possible that different locations of telocytes could be associated with different roles.

Interstitial Cajal-like cells of human Fallopian tube express estrogen and progesterone receptors

Cells of the female reproductive tract are subject to hormonal control via sex steroid genomic receptors expressed at nuclear level. We previously showed that interstitial Cajal-like cells (ICLC) of human myometrium expressed estrogen and progesterone receptors (ER/PR). Our aim, based on these results, was to see if ER and/or PR could be found also in tubal ICLC. Indeed, we present here immunohistochemical evidence that ICLC of human Fallopian tube (isthmic region) have such receptors. Stromal ICLC, as well as ICLC among smooth muscle layers, were identified in tissue sections by their morphological features (e.g. several very long, moniliform, prolongations of cell body) as well as by c-kit positivity, vital staining with methylene blue or silver impregnation. Additional evidence was provided by sequential staining for c-kit and for PR on the same cell, by 'sandwich method'. In vitro, the 4th passage cell cultures from Fallopian tube muscularis exhibiting ICLC morphology showed the presence of ER-alpha and/or PR-A by immunofluorescence. In conclusion, our data suggest that ICLC could function as steroid sensors, and might be implicated in Fallopian tube motility (via gap junctions or juxta- and/or paracrine mechanisms).

Measurement of intracellular chloride ion concentration in ICC in situ and in explant culture

BACKGROUND

Chloride channels are proposed to play a central role in the electrical pacemaking mechanism of interstitial cells of Cajal (ICC). A key unknown factor in the consideration of this role is the chloride equilibrium potential (E(Cl)), as determined by the relative concentrations of intra- ([Cl(-)](i)) and extracellular ([Cl(-)](o)) chloride ions.

METHODS

To calculate the E(Cl) of ICC, [Cl(-)](i) was measured with the fluorescent chloride indicator N-(6-methoxyquinolyl) acetoethyl ester (MQAE). Pacemaker ICC in explant cultures or in situ, i.e. ICC associated with the myenteric plexus of the small intestine, were loaded with MQAE and fluorescence was measured by laser scanning confocal microscopy. The dye fluorescence was then calibrated against known [Cl(-)](i) by treating the explants or in situ preparations with chloride ionophore and varying bath chloride concentrations.

KEY RESULTS

In explants, ICC [Cl(-)](i) was measured as 13 mmol L(-1) with [Cl(-)](o) of 100 mmol L(-1), giving an E(Cl) of -52 mV [corrected]. With [Cl(-)](o) at 166 mmol L(-1), [Cl(-)](i) was 26 mmol L(-1), giving an E(Cl) of -47 mV[corrected]. In situ, ICC [Cl(-)](i) was measured as 26 mmol L(-1) with [Cl(-)](o) of 130 mmol L(-1), giving an E(Cl) of -41 mV [corrected]. Importantly ICC compensate for changes in extracellular chloride by changing [Cl(-)](i) and thus maintain E(Cl). In ICC explant clusters, [Cl(-)](i) was seen to fluctuate, possibly evoked by rhythmic changes in intracellular calcium.

CONCLUSIONS & INFERENCES

The intracellular chloride concentration in ICC fluctuates to keep its equilibrium potential constant. The identification of E(Cl) as positive to the resting membrane potential of ICC indicates that opening of chloride channels will depolarize ICC.

Recent advances in studies of spontaneous activity in smooth muscle: ubiquitous pacemaker cells

The general and specific properties of pacemaker cells, including Kit-negative cells, that are distributed in gastrointestinal, urethral and uterine smooth muscle tissues, are discussed herein. In intestinal tissues, interstitial cells of Cajal (ICC) are heterogeneous in both their forms and roles. ICC distributed in the myenteric layer (ICC-MY) act as primary pacemaker cells for intestinal mechanical and electrical activity. ICC distributed in muscle bundles play a role as mediators of signals from autonomic nerves to smooth muscle cells. A group of ICC also appears to act as a stretch sensor. Intracellular Ca2+ dynamics play a crucial role in ICC-MY pacemaking; intracellular Ca2+ ([Ca2+](i)) oscillations periodically activate plasmalemmal Ca2+-activated ion channels, such as Ca2+-activated Cl(-) channels and/or non-selective cation channels, although the relative contributions of these channels are not defined. With respect to gut motility, both the ICC network and enteric nervous system, including excitatory and inhibitory enteric neurons, play an essential role in producing highly coordinated peristalsis.

Interstitial cells of Cajal in the cynomolgus monkey rectoanal region and their relationship to sympathetic and nitrergic nerves

The morphology of interstitial cells of Cajal (ICC) in the circular muscle layer of the cynomolgus monkey internal anal sphincter (IAS) and rectum and their relationship to sympathetic and nitrergic nerves were compared by dual-labeling immunohistochemistry. Contractile studies confirmed that nitrergic nerves participate in neural inhibition in both regions whereas sympathetic nerves serve as excitatory motor nerves only in the IAS. Muscle bundles extended from myenteric to submucosal edge in rectum but in the IAS bundles were further divided into "minibundles" each surrounded by connective tissue. Dual labeling of KIT and smooth muscle myosin revealed KIT-positive stellate-shaped ICC (ICC-IAS) within each minibundle. In the rectum intramuscular ICC (ICC-IM) were spindle shaped whereas stellate-shaped ICC were located at the myenteric surface (ICC-MY). ICC were absent from both the myenteric and submucosal surfaces of the IAS. Nitrergic nerves (identified with anti-neuronal nitric oxide synthase antibodies or NADPH diaphorase activity) and sympathetic nerves (identified with anti-tyrosine hydroxylase antibody) each formed a plexus at the myenteric surface of the rectum but not the IAS. Intramuscular neuronal nitric oxide synthase- and tyrosine hydroxylase-positive fibers were present in both regions but were only closely associated with ICC-IM in rectum. Minimal association was also noted between ICC-IAS and cells expressing the nonspecific neuronal marker PGP9.5. In conclusion, the morphology of rectal ICC-IM and ICC-MY is similar to that described elsewhere in the gastrointestinal tract whereas ICC-IAS are unique. The distribution of stellate-shaped ICC-IAS throughout the musculature and their absence from both the myenteric and submucosal surfaces suggest that ICC-IAS may serve as pacemaker cells in this muscle whereas their limited relationship to nerves suggests that they are not involved in neuromuscular transmission. Additionally, the presence of numerous minibundles, each containing both ICC-IAS and nerves, suggests that this muscle functions as a multiunit type muscle.

TELOCYTES - a case of serendipity: the winding way from Interstitial Cells of Cajal (ICC), via Interstitial Cajal-Like Cells (ICLC) to TELOCYTES

Ramon y Cajal discovered a particular cell type in the gut, which he named ‘interstitial neurons’ more that 100 years ago. In the early 1970s, electron microscopy/electron microscope (EM) studies showed that indeed a special interstitial cell type corresponding to the cells discovered by Cajal is localized in the gut muscle coat, but it became obvious that they were not neurons. Consequently, they were renamed ‘interstitial cells of Cajal’ (ICC) and considered to be pace-makers for gut motility. For the past 10 years many groups were interested in whether or not ICC are present outside the gastrointestinal tract, and indeed, peculiar interstitial cells were found in: upper and lower urinary tracts, blood vessels, pancreas, male and female reproductive tracts, mammary gland, placenta, and, recently, in the heart as well as in the gut. Such cells, now mostly known as interstitial Cajal-like cells (ICLC), were given different and confusing names. Moreover, ICLC are only apparently similar to canonical ICC. In fact, EM and cell cultures revealed very particular features of ICLC, which unequivocally distinguishes them from ICC and all other interstitial cells: the presence of 2–5 cell body prolongations that are very thin (less than 0.2 μm, under resolving power of light microscopy), extremely long (tens to hundreds of μm), with a moniliform aspect (many dilations along), as well as caveolae. Given the unique dimensions of these prolongations (very long and very thin) and to avoid further confusion with other interstitial cell types (e.g. fibroblast, fibrocyte, fibroblast-like cells, mesenchymal cells), we are proposing the term TELOCYTES for them, and TELOPODES for their prolongations, by using the Greek affix ‘telos’.

Heterogeneities in ICC Ca2+ activity within canine large intestine

BACKGROUND & AIMS

In human and canine colon, both slow (slow waves, 2-8/min) and fast (myenteric potential oscillations [MPOs]; 16-20/min) electrical rhythms in the smooth muscle originate at the submucosal and myenteric borders, respectively. We used Ca(2+) imaging to investigate whether interstitial cells of Cajal (ICCs) at these borders generated distinct rhythms.

METHODS

Segments of canine colon were pinned with submucosal or myenteric surface uppermost or cut in cross section. Tissues were loaded with a Ca(2+) indicator (fluo-4), and activity was monitored at 36.5 +/- 0.5 degrees C using an electron multiplying charge coupled device (EMCCD).

RESULTS

Rhythmic, biphasic Ca(2+) transients (5-8/min), similar in waveform to electrical slow waves, propagated without decrement as a wave front (2-5 mm/s) through the ICC-SM network lying along the submucosal surface of the circular muscle (CM). In contrast, rhythmic intracellular Ca(2+) waves (approximately 16/min) and spontaneous reductions in Ca(2+) were observed in ICCs at the myenteric border (ICC-MY). Normally, intracellular Ca(2+) waves were unsynchronized between adjacent ICC-MY, although excitatory nerve activity synchronized activity. In addition, spontaneous reductions in Ca(2+) were observed that inhibited Ca(2+) waves. N omega-nitro-L-arginine (100 micromol/L; nitric oxide antagonist) blocked the reductions in Ca(2+) and increased the frequency (approximately 19/min) of intracellular Ca(2+) waves within ICC-MY.

CONCLUSIONS

ICC-SMs form a tightly coupled network that is able to generate and propagate slow waves. In contrast, Ca(2+) transients in ICC-MYs, which are normally not synchronized, have a similar duration and frequency as MPOs. Like MPOs, their activity is inhibited by nitrergic nerves and synchronized by excitatory nerves.

Inositol trisphosphate-dependent Ca stores and mitochondria modulate slow wave activity arising from the smooth muscle cells of the guinea pig prostate gland

BACKGROUND AND PURPOSE

Changes in smooth muscle tone of the prostate gland are involved in aetiology of symptomatic prostatic hyperplasia, however the control mechanisms of prostatic smooth muscle are not well understood. Here, we have examined the role of internal Ca(2+) compartments in regulating slow wave activity in the guinea pig prostate.

EXPERIMENTAL APPROACH

Standard intracellular membrane potential recording techniques were used.

KEY RESULTS

The majority (89%) of impaled cells displayed 'slow wave' activity. Cyclopiazonic acid (10 micromol.L(-1)) transiently depolarized (3-9 mV) the membrane potential of the prostatic stroma and transiently increased slow wave frequency. Thereafter, slow wave frequency slowly decreased over 20-30 min. Ryanodine transiently increased slow wave frequency, although after 30 min exposure slow wave frequency and time course returned to near control values. Caffeine (1 mmol.L(-1)) reduced slow wave frequency, accompanied by membrane depolarization of about 8 mV. Blockade of inositol trisphosphate receptor (IP(3)R)-mediated Ca(2+) release with 2-aminoethoxy-diphenylborate (60 micromol.L(-1)) or Xestospongin C (3 micromol.L(-1)) or inhibiting phospholipase C and IP(3) formation using U73122 (5 micromol.L(-1)) or neomycin (1 and 4 mmol.L(-1)) reduced slow wave frequency, amplitude and duration. The mitochondrial uncouplers, p-trifluoromethoxy carbonyl cyanide phenyl hydrazone (1-10 micromol.L(-1)), carbonyl cyanide m-chlorophenylhydrazone (1-3 micromol.L(-1)) or rotenone (10 micromol.L(-1)), depolarized the membrane (8-10 mV) before abolishing electrical activity.

CONCLUSION AND IMPLICATIONS

These results suggest that slow wave activity was dependent on the cyclical release of Ca(2+) from IP(3)-controlled internal stores and mitochondria. This implies that intracellular compartments were essential in the initiation and/or maintenance of the regenerative contractile activity in the guinea pig prostate gland.

Mechanisms of action of intravesical botulinum treatment in refractory detrusor overactivity

Urinary retention is one of a multitude of autonomic deficits resulting from acute botulism (oral botulinum intoxication). The powerful influence of botulinum-A neurotoxin (BoNT-A) on autonomic function has now been harnessed to the benefit of patients with detrusor overactivity (DO), by injecting the agent intramurally, with consequent improvement in urodynamic and clinical variables. Nonetheless, the complexity of bladder cellular physiology and putative mechanisms underlying the pathophysiological basis of DO even now render the precise mechanisms of clinical response to intravesical BoNT-A uncertain. In this review, the processes by which BoNT-A affects nerve function and the state-of-the-art in the physiological understanding of bladder dysfunction are discussed together, conveying how much must be reckoned when attempting to understand the mechanisms by which this powerful agent can improve refractory and bothersome DO.

Role of mitochondria in modulation of spontaneous Ca2+ waves in freshly dispersed interstitial cells of Cajal from the rabbit urethra

Interstitial cells of Cajal (ICC) isolated from the rabbit urethra exhibit pacemaker activity that results from spontaneous Ca(2+) waves. The purpose of this study was to investigate if this activity was influenced by Ca(2+) uptake into mitochondria. Spontaneous Ca(2+) waves were recorded using a Nipkow spinning disk confocal microscope and spontaneous transient inward currents (STICs) were recorded using the whole-cell patch clamp technique. Disruption of the mitochondrial membrane potential with the electron transport chain inhibitors rotenone (10 microm) and antimycin A (5 microm) abolished Ca(2+) waves and increased basal Ca(2+) levels. Similar results were achieved when mitochondria membrane potential was collapsed using the protonophores FCCP (0.2 microm) and CCCP (1 microm). Spontaneous Ca(2+) waves were not inhibited by the ATP synthase inhibitor oligomycin (1 microm), suggesting that these effects were not attributable to an effect on ATP levels. STICs recorded under voltage clamp at -60 mV were also inhibited by CCCP and antimycin A. Dialysis of cells with the mitochondrial uniporter inhibitor RU360 (10 microm) also inhibited STICS. Stimulation of Ca(2+) uptake into mitochondria using the plant flavonoid kaempferol (10 microm) induced a series of propagating Ca(2+) waves. The kaempferol-induced activity was inhibited by application of caffeine (10 mm) or removal of extracellular Ca(2+), but was not significantly affected by the IP(3) receptor blocker 2-APB (100 microm). These data suggest that spontaneous Ca(2+) waves in urethral ICC are regulated by buffering of cytoplasmic Ca(2+) by mitochondria.

Damage to the bladder neck alters autonomous activity and its sensitivity to cholinergic agonists

OBJECTIVE

To identify and describe changes to the motor component of the motor/sensory system, which contributes to sensation during the filling phase of the micturition cycle, as a result of surgically induced bladder pathology, i.e. damage to the bladder neck and outlet obstruction.

MATERIALS AND METHODS

Adult male guinea pigs (294-454 g) were assigned initially into three groups: (i) normal guinea pigs with no surgical intervention (control, seven); (ii) guinea pigs which, with full surgical anaesthesia, had a silver ring implanted around the bladder neck (obstructed, 13); and (iii) guinea pigs operated to expose the bladder neck but with no implantation of a ring (sham, six). At 2-4 weeks after surgery the bladders were isolated, weighed and the pressure recordings used to identify autonomous activity.

RESULTS

The bladder weights in all operated groups, including the sham, were greater than controls. Bladder weights in the obstructed guinea pigs varied considerably, reflecting the degree of pathological change. Consequently, bladders from this group were divided into those with high (OBH) and those with low bladder weight (OBL). The mean (sd) amplitudes of the autonomous contractions were 1.1 (0.1), 10.8 (1.8), 11.4 (2.5) and 17.1 (4.0) cmH(2)O in control, sham, OBL and OBH bladders, respectively, indicating a progressive alteration in function with the pathology. The changes in the sham group suggested that the pathological changes were not the result of obstruction but damage to the bladder neck, the implantation of the silver rings exacerbating the damage. There were episodes of rapid phasic activity (bursts) in 10 of 13 of the ring-implanted bladders, and in two of six in the sham group, but never in controls. Neither the autonomous activity nor the bursts were affected by tetrodotoxin (1 microm) or atropine (3 microm) but they were abolished by noradrenaline (3 microm). In control bladders, adding the muscarinic agonist arecaidine produced a transient acceleration of phasic activity and increased the amplitude of the contractions. There was a similar acceleration of activity in all the operated groups but the concentrations needed to achieve an increase in frequency were significantly lower, the relative sensitivity to arecaidine being OBH >/= OBL > sham > control.

CONCLUSION

The mechanism involved in controlling the frequency of the motor component of the motor/sensory system, the 'pacemaker', appears to become progressively 'supersensitive' to cholinergic stimulation with the development of pathology. These observations are discussed in relation to the motor/sensory system and the origins of sensation in the bladder. The argument is proposed that damage to the bladder neck, not obstruction per se, results in altered nonmicturition activity which contributes to increased afferent output. In turn this contributes to the increased sensations of urge associated with bladder dysfunction. The cholinergic regulation of this altered 'pacemaker' might be the target for one of the therapeutic actions of anticholinergic drugs.

Interstitial Cajal-like cells in human gallbladder

We describe here an interstitial Cajal-like cell type (ICLC) in human gallbladder, resembling the archetypal enteric interstitial cells of Cajal. Gallbladder ICLC were demonstrated in fresh preparations (tissue cryosections) using methylene-blue, and fixed specimens in Epon semi-thin sections stained with toluidine blue or transmission electron microscopy (TEM). The positive diagnosis of gallbladder ICLC was further verified by immunohistochemistry: CD117/c-kit, CD34, and another 16 antigens: vimentin, desmin, nestin, alpha-smooth muscle actin, NK-1, S-100, PGP-9.5, tau protein, chromogranin A, NSE, GFAP, CD1a, CD62-P, CD68, estrogen and progesterone receptors. Double immunostaining was performed for CD117, CD34 and CD117 and nestin, respectively. In fresh specimens, the spatial density of gallbladder ICLC was 100-110 cells/mm(2). ICLC mainly appeared beneath the epithelium and in muscularis (about 7%, and approximately 5%, respectively). In toto, ICLC represent in gallbladder approximately 5.5% of subepithelial cells. TEM showed that diagnostic criteria were fulfilled by ICLC. Moreover, TEM indicated that the main ultrastructural distinctive feature for ICLC, the cell processes, develop into the characteristic shape at a relatively early stage of development. It remains to be established if, in humans, ICLC are involved in gallbladder (dis)functions (e.g. pace-making, secretion (auto-, juxta- and/or paracrine), intercellular signaling, or stone formation).

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).

Interstitial cells of Cajal (ICC) and gastrointestinal stromal tumor (GIST): facts, speculations, and myths

Interstitial cells of Cajal (ICC) is a peculiar cell network composed of cells having processes described by the eminent Spanish neuroanatomist of the 19th century, S. Ramon y Cajal. ICC became a fascinating subject to many investigators and it is estimated that there are over 100 publications yearly on the subject related to ICC, in the last three years. Now it is widely accepted that ICC are pace maker cells of the gut and probable progenitor cells of gastrointestinal stromal tumors (GIST). Lately, interstitial Cajal-like cells (ICLC) are being found in various organs and their physiological role is still to be defined. We have reviewed the literature trying to evaluate the validity of the current concept and found that there are a few salient points to be considered. 1) There has been some important departure in defining the identity of ICC from the original criteria of Cajal. In particular, ICC with myoid feafures in intestinal smooth muscle layers (ICC-DPM) do not seem to fit to the original description of interstitial cell network by Cajal. We have also pointed out that the current reports assigning a pace maker role to ICC vastly depend on the scientific data on "ICC with myoid features", not on "fibroblast-like ICC", which are more abundant and easier to identify. 2) There seem to be an overwhelming amount of data proving the relationship between ICC and GIST. Both are known to express c-Kit and the ultrastructural characteristics seen in GIST roughly parallel those of ICC including minimal myoid differentiation seen in the majority of GIST, supporting the current concept that GIST are ICC tumors. 3) According to the original description of Cajal, ICC was not limited to the gut, suggesting an existence of ICC in other organs. The list of organs reported to contain ICC (currently identified by immunohistochemistry and electron microscopy) is ever growing and further studies are needed to define their identity and pathophysiologic role. 4). Recent data concerning gut development suggest that both c-Kit expressing ICC (fibroblasts-like as well as muscle-like) and gut muscle cells derive from the common progenitor cells of the embryonic gut unifying the histogenetic concept of all GIST with heterogeneous cytomorphologic features. In this review we attempted to incorporate recent information on interstitial Cajal-like cells (ICLC) found in other organs to broaden our understanding of ICC in general in terms of their ultrastructure, physiology, and neoplasia.

Ca2+ signalling in urethral interstitial cells of Cajal

Interstitial cells of Cajal (ICC) in the urethra have been proposed as specialized pacemakers that are involved in the generation of urethral tone and therefore the maintenance of urinary continence. Recent studies on freshly dispersed ICC from the urethra of rabbits have demonstrated that pacemaker activity in urethra ICC is characterized by spontaneous transient depolarizations (STDs) under current clamp and spontaneous transient inward currents (STICs) under voltage clamp. When these events were simultaneously recorded with changes in intracellular Ca(2+) (using a Nipkow spinning disk confocal microscope) they were found to be associated with global Ca(2+) oscillations. In this short review we will consider some of these recent findings regarding the contribution of intracellular Ca(2+) stores and Ca(2+) influx to the generation of pacemaker activity in urethral ICC with particular emphasis on the contribution of reverse Na(+)/Ca(2+) exchange (NCX).

Interstitial Cajal-like cells (ICLC) as steroid hormone sensors in human myometrium: immunocytochemical approach

Expression of estrogen (ER) and progesterone (PR) receptors was investigated in cultured human normal myometrial cells (non-pregnant uterus, fertile period). The ER and PR expression was studied by immunohistochemistry and immunofluorescence on either myocytes or interstitial Cajal-like cells (ICLC). Only those cells double immunostained for c-kit and steroid receptors were considered as ICLC. ER and/or PR immunoreactivity was localized in ICLC, primarily concentrated at the nucleus level, but it was also observed in the cell body (cytoplasm) and processes. Stronger immunopositive reaction in the ICLC nucleus for PR than for ER was noted. Under our experimental conditions, a clear positive repeatable reaction for steroid receptors could not be detected in myocytes. In conclusion, these data suggest that ICLC could be true hormonal 'sensors', possibly participating in the regulation of human myometrial contractions (via gap junctions with myocytes and/or by paracrine signaling).

Insights into the interstitium of ventricular myocardium: interstitial Cajal-like cells (ICLC)

We have previously described interstitial Cajal-like cells (ICLC) in human atrial myocardium. Several complementary approaches were used to verify the existence of ICLC in the interstitium of rat or human ventricular myocardium: primary cell cultures, vital stainings (e.g.: methylene blue), traditional stainings (including silver impregnation), phase contrast and non-conventional light microscopy (Epon-embedded semithin sections), transmission electron microscopy (TEM) (serial ultrathin sections), stereology, immunohistochemistry (IHC) and immunofluorescence (IF) with molecular probes. Cardiomyocytes occupy about 75% of rat ventricular myocardium volume. ICLC represent approximately 32% of the number of interstitial cells and the ratio cardiomyocytes/ICLC is about 70/1. In the interstitium, ICLC establish close contacts with nerve fibers, myocytes, blood capillaries and with immunoreactive cells (stromal synapses). ICLC show characteristic cytoplasmic processes, frequently two or three, which are very long (tens up to hundreds of microm), very thin (0.1-0.5 microm thick), with uneven caliber, having dilations, resulting in a moniliform aspect. Gap junctions between such processes can be found. Usually, the dilations are occupied by mitochondria (as revealed by Janus green B and MitoTracker Green FM) and elements of endoplasmic reticulum. Characteristically, some prolongations are flat, with a veil-like appearance, forming a labyrinthic system. ICLC display caveolae (about 1 caveola/ 1 microm cell membrane length, or 2-4% of the relative cytoplasmic volume). Mitochondria and endoplasmic reticulum (rough and smooth) occupy 5-10% and 1-2% of cytoplasmic volume, respectively. IHC revealed positive staining for CD34, EGFR and vimentin and, only in a few cases for CD117. IHC was negative for: desmin, CD57, tau, chymase, tryptase and CD13. IF showed that ventricular ICLC expressed connexin 43. We may speculate that possible ICLC roles might be: intercellular signaling (neurons, myocytes, capillaries etc.) and/or chemomechanical sensors. For pathology, it seems attractive to think that ICLC might participate in the process of cardiac repair/remodeling, arrhythmogenesis and, eventually, sudden death.