5-Hydroxytryptamine Enhances the Pacemaker Activity of Interstitial Cells of Cajal in Mouse Colon

We examined the localization of the 5-hydroxytryptamine (5-HT) receptor and its effects on mouse colonic interstitial cells of Cajal (ICCs) using electrophysiological techniques. Treatment with 5-HT increased the pacemaker activity in colonic ICCs with depolarization of membrane potentials in a dose-dependent manner. Hyperpolarization-activated cyclic nucleotide-gated (HCN) channel blockers blocked pacemaker activity and 5-HT-induced effects. Moreover, an adenylate cyclase inhibitor inhibited 5-HT-induced effects, and cell-permeable 8-bromo-cAMP increased the pacemaker activity. Various agonists of the 5-HT receptor subtype were working in colonic ICCs, including the 5-HT4 receptor. In small intestinal ICCs, 5-HT depolarized the membrane potentials transiently. Adenylate cyclase inhibitors or HCN blockers did not show any influence on 5-HT-induced effects. Anoctamin-1 (ANO1) or T-type Ca2+ channel blockers inhibited the pacemaker activity of colonic ICCs and blocked 5-HT-induced effects. A tyrosine protein kinase inhibitor inhibited pacemaker activity in colonic ICCs under controlled conditions but did not show any influence on 5-HT-induced effects. Among mitogen-activated protein kinase (MAPK) inhibitors, a p38 MAPK inhibitor inhibited 5-HT-induced effects on colonic ICCs. Thus, 5-HT's effect on pacemaker activity in small intestinal and colonic ICCs has excitatory but variable patterns. ANO1, T-type Ca2+, and HCN channels are involved in 5-HT-induced effects, and MAPKs are involved in 5-HT effects in colonic ICCs.

Is bladder outlet obstruction rat model to induce overactive bladder (OAB) has similarity to human OAB? Research on the events in smooth muscle, collagen, interstitial cell and telocyte distribution

BACKGROUND

Cellular and cytoskeletal events of overactive bladder (OAB) have not been sufficiently explored in human bladder due to different limitations. Bladder outlet obstruction (BOO) had been induced in different animal models with different methods to induce (OAB). Similarity of the animal models of BOO to the human OAB is postulated but has not been confirmed. The interstitial cells of Cajal (ICCs), and telocytes (TCs) are an important players in smooth muscles conductivity, they had not been well investigated in the previous BOO models. Objectives are to investigate the morphological pattern of cellular, cytoskeleton and telocytes distribution in BOO rat model and to match the events in two time periods and compare it to the findings in real-world human OAB.

METHODS

Female Sprague-Dawley rats (Rattus norvegicus) were randomly divided into: sham (n = 10), BOO 6 W (n = 10), BOO 8 W (n = 10). Operative procedure to Induce BOO was done under anesthesia with intraperitoneal Ketamine administration. The Effect of induction of BOO was evaluated after 6 and 8 weeks. The rats were anesthetized, and the urinary bladder was removed, while the rat was unconscious under anaesthesia it was transferred to the inhalation anaesthesia cage for euthanasia, rats were sacrificed under light anesthesia using isoflurane. Care of animals, surgical procedure, and euthanasia adhered to Guide for the Care and Use of Laboratory Animals, and AVMA Guidelines for the Euthanasia of Animals. The retrieved bladder was processed for examination with histopathology, immunohistochemistry (IHC), and transmission electron microscopy (EM).

RESULTS

Histological examination of the bladder shows thinner urothelium, condensation of collagen between muscle bundles. IHC with c-kit shows the excess distribution of ICCs between smooth muscle bundles. EM shows frequent distribution of TCs that were situated between collagen fibers. Finings in BOO 6 W group and BOO 8 W group were comparable.

CONCLUSION

The animal model study demonstrated increased collagen/ smooth muscle ratio, high intensity of ICCs and presence of TCs. Findings show that a minimally invasive procedure to induce BOO in rats had resulted in an OAB that has morphological changes that were stable in 6 & 8 weeks. We demonstrated the distribution of TCs and ICCs in the rat animal model and defined them. The population of TCs in the BOO rat model is described for the first time, suggests that the TCs and ICCs may contribute to the pathophysiology of OAB. Similarity of animal model to human events OAB was demonstrated. These findings warrant further study to define the role of TCs in OAB.

CLINICAL TRIAL REGISTRY

The study does not require a clinical trial registration; it is an experimental animal study in basic science and does not include human subjects.

Idiopathic Slow Transit Constipation: Pathophysiology, Diagnosis, and Management

Slow transit constipation (STC) has an estimated prevalence of 2-4% of the general population, and although it is the least prevalent of the chronic constipation phenotypes, it more commonly causes refractory symptoms and is associated with significant psychosocial stress, poor quality of life, and high healthcare costs. This review provides an overview of the pathophysiology, diagnosis, and management options in STC. STC occurs due to colonic dysmotility and is thought to be a neuromuscular disorder of the colon. Several pathophysiologic features have been observed in STC, including reduced contractions on manometry, delayed emptying on transit studies, reduced numbers of interstitial cells of Cajal on histology, and reduced amounts of excitatory neurotransmitters within myenteric plexuses. The underlying aetiology is uncertain, but autoimmune and hormonal mechanisms have been hypothesised. Diagnosing STC may be challenging, and there is substantial overlap with the other clinical constipation phenotypes. Prior to making a diagnosis of STC, other primary constipation phenotypes and secondary causes of constipation need to be ruled out. An assessment of colonic transit time is required for the diagnosis and can be performed by a number of different methods. There are several different management options for constipation, including lifestyle, dietary, pharmacologic, interventional, and surgical. The effectiveness of the available therapies in STC differs from that of the other constipation phenotypes, and prokinetics often make up the mainstay for those who fail standard laxatives. There are few available management options for patients with medically refractory STC, but patients may respond well to surgical intervention. STC is a common condition associated with a significant burden of disease. It can present a clinical challenge, but a structured approach to the diagnosis and management can be of great value to the clinician. There are many therapeutic options available, with some having more benefits than others.

Haustral rhythmic motor patterns of the human large bowel revealed by ultrasound

Effective and widely available strategies are needed to diagnose colonic motility dysfunction. We investigated whether ultrasonography could generate spatiotemporal maps combined with motor pattern frequency analysis, to become a noninvasive method to characterize human colon motor patterns. Abdominal colonic ultrasonography was performed on healthy subjects (N = 7), focusing on the detailed recording of spontaneous haustral activities. We developed image segmentation and frequency analysis software to analyze the motor patterns captured. Ultrasonography recordings of the ascending, transverse, and descending colon identified three distinct rhythmic motor patterns: the 1 cycle/min and the 3 cycles/min cyclic motor pattern were seen throughout the whole colon, whereas the 12 cycles/min cyclic motor pattern was identified in the ascending colon. The rhythmic motor patterns of the human colon that are associated with interstitial cells of Cajal-associated pacemaking activity can be accurately identified and quantified using ultrasound.NEW & NOTEWORTHY Ultrasonography in the clinical field is an underutilized tool for assessing colonic motility; however, with the addition of frequency analysis techniques, it provides a method to identify human colonic motor patterns. Here we report on the 1, 3, and 12 cpm rhythmic motor patterns. Ultrasound has the potential to become a bedside assessment for colonic dysmotility and may reveal the health of interstitial cells of Cajal (ICC) pacemaker activities.

Distribution and Ultrastructural Features of Telocytes in the Pars Distalis of the Rat Pituitary Gland

Telocytes (TCs), a novel type of interstitial cells, are characterized by their smaller cellular body and extremely long, thin processes which are called telopodes (Tps). They have been described in multiple organs from diverse animals. Currently, the existence of TCs in rat pars distalis (PD) has remained unexplored. This investigation was undertaken to visualize the distribution and structural features of TCs in the PD using immunofluorescence (IF) and further validated by transmission electron microscopy (TEM). HE staining revealed the presence of interstitial cells in the peri-sinusoidal vessels spaces of the PD. Using IF, CD34/vimentin double-positive interstitial cells were identified as TCs in accordance with identification standards. TEM further verified the presence of TCs based on their unique ultrastructural features. TCs exhibited communication structures including cell connections and extracellular vesicles (EVs). Interestingly, TCs were in close proximity to the nerves. Most importantly, Tps extended toward the nerves, blood vessels, and glandular cells. TCs could be the structural foundation of a third regulatory system in rat PD according to the tight connections of TCs with sinusoid vessels, glandular cells, EVs and most crucially the nerves. Taken together, these morphological and structural findings demonstrate that TCs are vital components of the rat PD.

Interstitial Cell Dysregulation in Allergic Contact Dermatitis: A Morphodynamic Study of Novel Interstitial Cell Telocytes

Allergic contact dermatitis (ACD) is an occupation-dependent skin disease that afflicts humans with recurrent, non-specific episodes. Telocyte (TC) is a novel interstitial cell discovered in recent years and, together with fibroblasts, constitutes the predominant interstitial cell population in the skin. The purpose of this study was to investigate the morphodynamic changes of interstitial cells, especially TCs, in the skin during the development and treatment of ACD by histological and microscopic scientific methods. Hematoxylin-eosin staining, Masson staining, immunohistochemistry (IHC), immunofluorescence (IF), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were used to track morphodynamic changes in interstitial cells during the development and treatment in the ACD-involved skin induced by 2,4-dinitrochlorobenzene (DNCB). The results demonstrated that TCs were mainly present around dermal collagen fibers, perivascular (except dermal papillary vascular loop), and skin appendages, which expressed CD34+, Vimentin+, PDGFR-α+, and α-SMA-. The absence of TCs during ACD development and after ACD recovery causes dermal interstitial cell dysregulation. The special anatomical relationships between TCs, immune cells, and follicular stem cells were also revealed, suggesting their potential dermatitis-regulating function. In a nutshell, our results provide morphodynamic evidence for the process of ACD development and recovery and offer potential cytological ideas for ACD treatment.

Smooth muscle cells, interstitial cells and neurons in the gallbladder (GB): Functional syncytium of electrical rhythmicity and GB motility (Review)

The motility of the gallbladder (GB) involves the storage, concentration and delivery of bile. GB motor functions are controlled by multiple complex factors, such as extrinsic and intrinsic innervation, humoral factors and neuropeptides. GB emptying results from coordinated contractions of the muscular layers of the GB wall. Depolarization of GB smooth muscle (GBSM) depends on the activation of the regular depolarization‑repolarization potential, referred to as slow waves (SWs). These rhythmic SWs of GBSM contraction are mediated by several cell types, including smooth muscle cells (SMCs), GB neurons, telocytes (TC) and specialized pacemaker cells called interstitial cells of Cajal (ICC). The present article introduced a new GB motor unit, the SMC‑TC‑ICC‑neuron (STIN) syncytium. In GB, STIN cells provide pacemaker activity, propagation pathways for SWs, transduction of inputs from motor and sensory neurons and mechanosensitivity. The present review provided an overview of STIN cells, mechanisms generating GBSM contractile behavior and GB motility, and discussed alterations of STIN cell function under different disease conditions.

Renal interstitial cells to the rescue

The ability of the adult zebrafish to replace damaged nephrons in the kidney depends on renal progenitor cells and renal interstitial cells working closely together.

Distributions of Platelet-Derived Growth Factor Receptor-α Positive Cells and Interstitial Cells of Cajal in the Colon of Rats with Diabetes Mellitus Type 2

Background and Objectives: Diabetic gastroenteropathy (DG) is a common complication of diabetes mellitus type 2. Interstitial cells are non-neural cells of mesenchymal origin inserted between nerve elements and smooth muscle cells, necessary for normal function and peristaltic contractions in the gastrointestinal (GI) tract. There are at least two types of interstitial cells within the GI muscle layer-interstitial cells of Cajal (ICC) and interstitial platelet-derived growth factor receptor α-positive cells (IPC). The mechanism of diabetic gastroenteropathy is unclear, and interstitial cells disorders caused by metabolic changes in diabetes mellitus (DM) could explain the symptoms of DG (slow intestinal transit, constipation, fecal incontinence). The aim of this study was to identify PDGFRα and c-kit immunoreactive cells in the colon of rats with streptozotocin-nicotinamide-induced diabetes mellitus type 2, as well as to determine their distribution in relation to smooth muscle cells and enteric nerve structures. Materials and Methods: Male Wistar rats were used, and diabetes type 2 was induced by an intraperitoneal injection of streptozotocin, immediately after intraperitoneal application of nicotinamide. The colon specimens were exposed to PDGFRα and anti-c-kit antibodies to investigate interstitial cells; enteric neurons and smooth muscle cells were immunohistochemically labeled with NF-M and desmin antibodies. Results: Significant loss of the intramuscular ICC, myenteric ICC, and loss of their connection in intramuscular linear arrays and around the ganglion of the myenteric plexus were observed with no changes in nerve fiber distribution in the colon of rats with diabetes mellitus type 2. IPC were rarely present within the colon muscle layer with densely distributed PDGFRα+ cells in the colon mucosa and submucosa of both experimental groups. In summary, a decrease in intramuscular ICC, discontinuities and breakdown of contacts between myenteric ICC without changes in IPC and nerve fibers distribution were observed in the colon of streptozotocin/nicotinamide-induced diabetes type 2 rats.

Mechanosensing in the Physiology and Pathology of the Gastrointestinal Tract

Normal gastrointestinal function relies on sensing and transducing mechanical signals into changes in intracellular signaling pathways. Both specialized mechanosensing cells, such as certain enterochromaffin cells and enteric neurons, and non-specialized cells, such as smooth muscle cells, interstitial cells of Cajal, and resident macrophages, participate in physiological and pathological responses to mechanical signals in the gastrointestinal tract. We review the role of mechanosensors in the different cell types of the gastrointestinal tract. Then, we provide several examples of the role of mechanotransduction in normal physiology. These examples highlight the fact that, although these responses to mechanical signals have been known for decades, the mechanosensors involved in these responses to mechanical signals are largely unknown. Finally, we discuss several diseases involving the overstimulation or dysregulation of mechanotransductive pathways. Understanding these pathways and identifying the mechanosensors involved in these diseases may facilitate the identification of new drug targets to effectively treat these diseases.

Notes about telocytes and immunity

The interstitial cells known as telocytes have been described in various organs. Their role in the normal physiology and pathogenesis of numerous diseases is well known. They have been described in the context of various diseases (gallstone disease, endometriosis, uterine myoma, hydronephrosis, myocardial infraction, psoriasis, etc.), while their impact on inflammation, involvement in angiogenesis, and repair highlights their part in local homeostasis. What is known about their relationship with the immune system? Their secretomes, genome, immune profiles, contacts with surrounding cells, and specific localization allow us to give a possible explanation for their involvement in pathological pathways. This review aims to present the roles and features of telocytes in the context of intestinal immunity (the largest in our body), in the spleen, their interactions with immunocytes, and their place in stem cell niches.

Relationship between gallstones and interstitial cells of Cajal in the gallbladder

INTRODUCTION

A high percentage of patients with gallstones exhibit abnormalities in gallbladder emptying, and gallstones are often associated with gallbladder contraction. Interstitial cells of Cajal (ICC) in the gallbladder are involved in the generation and spreading of spontaneous contractions of the gallbladder. This study examined the relationship among the number of gallbladder ICC, gallbladder contractility, and gallstones.

MATERIALS AND METHODS

Forty-six patients, who underwent cholecystectomy within 3 months of enduring a gallbladder ejection fraction scan, were enrolled in this study. ICC were identified using a microscope after immunohistochemical staining for CD117/c-kit. Five high-power field (magnification 400×) units were randomly assigned, and the number of ICC in the mucosal and muscular layers was counted. These counts were compared according to the sex, age, reason for cholecystectomy, presence of gallstone, presence of gallbladder polyp, gallbladder ejection fraction, and gallbladder size for each patient.

RESULTS

The number of ICC in the mucosal layer was increased in the male participants (154.4 ± 73.9) compared with the female participants (107.3 ± 75.2); however, the ICC in the muscular layer was not different between the 2 groups. Additionally, the ICC in the mucosal and muscular layers did not differ according to age, cause of cholecystectomy, number of stones, stone character, stone diameter, or the presence of polyps. A larger gallbladder size was correlated with a decreased number of ICC in the muscular layer of the gallbladder. Additionally, when the number of gallbladder stones was increased, the number of ICC in the muscular layer of the gallbladder was decreased; however, there was no significant correlation between the number of ICC in the mucosal layer of the gallbladder and any of the following factors: age, GBEF, gallbladder size, stone number, or diameter. Furthermore, there was no significant correlation between the number of ICC in the muscular layer of the gallbladder, regardless of age, GBEF, and stone diameter.

CONCLUSION

Although we were unable to achieve significant results regarding the relationship between GBEF and ICC, this is the first human study to reveal the relationship among ICC, gallbladder size, and the number of gallstones.

Changes in interstitial cells and gastric excitability in a mouse model of sleeve gastrectomy

Obesity is a critical risk factor of several life-threatening diseases and the prevalence in adults has dramatically increased over the past ten years. In the USA the age-adjusted prevalence of obesity in adults was 42.4%, i.e., with a body mass index (BMI, weight (kg)/height (m)²) that exceeds 30 kg/m². Obese individuals are at the higher risk of obesity-related diseases, co-morbid conditions, lower quality of life, and increased mortality more than those in the normal BMI range i.e., 18.5–24.9 kg/m². Surgical treatment continues to be the most efficient and scientifically successful treatment for obese patients. Sleeve gastrectomy or vertical sleeve gastrectomy (VSG) is a relatively new gastric procedure to reduce body weight but is now the most popular bariatric operation. To date there have been few studies examining the changes in the cellular components and pacemaker activity that occur in the gastric wall following VSG and whether normal gastric activity recovers following VSG. In the present study we used a murine model to investigate the chronological changes of gastric excitability including electrophysiological, molecular and morphological changes in the gastric musculature following VSG. There is a significant disruption in specialized interstitial cells of Cajal in the gastric antrum following sleeve gastrectomy. This is associated with a loss of gastric pacemaker activity and post-junctional neuroeffector responses. Over a 4-month recovery period there was a gradual return in interstitial cells of Cajal networks, pacemaker activity and neural responses. These data describe for the first time the changes in gastric interstitial cells of Cajal networks, pacemaker activity and neuroeffector responses and the time-dependent recovery of ICC networks and normalization of motor activity and neural responses following VSG.

Propulsive colonic contractions are mediated by inhibition-driven poststimulus responses that originate in interstitial cells of Cajal

The peristaltic reflex is a fundamental behavior of the gastrointestinal (GI) tract in which mucosal stimulation activates propulsive contractions. The reflex occurs by stimulation of intrinsic primary afferent neurons with cell bodies in the myenteric plexus and projections to the lamina propria, distribution of information by interneurons, and activation of muscle motor neurons. The current concept is that excitatory cholinergic motor neurons are activated proximal to and inhibitory neurons are activated distal to the stimulus site. We found that atropine reduced, but did not block, colonic migrating motor complexes (CMMCs) in mouse, monkey, and human colons, suggesting a mechanism other than one activated by cholinergic neurons is involved in the generation/propagation of CMMCs. CMMCs were activated after a period of nerve stimulation in colons of each species, suggesting that the propulsive contractions of CMMCs may be due to the poststimulus excitation that follows inhibitory neural responses. Blocking nitrergic neurotransmission inhibited poststimulus excitation in muscle strips and blocked CMMCs in intact colons. Our data demonstrate that poststimulus excitation is due to increased Ca2+ transients in colonic interstitial cells of Cajal (ICC) following cessation of nitrergic, cyclic guanosine monophosphate (cGMP)-dependent inhibitory responses. The increase in Ca2+ transients after nitrergic responses activates a Ca2+-activated Cl− conductance, encoded by Ano1, in ICC. Antagonists of ANO1 channels inhibit poststimulus depolarizations in colonic muscles and CMMCs in intact colons. The poststimulus excitatory responses in ICC are linked to cGMP-inhibited cyclic adenosine monophosphate (cAMP) phosphodiesterase 3a and cAMP-dependent effects. These data suggest alternative mechanisms for generation and propagation of CMMCs in the colon.

Changes in esophagus interstitial cells of Cajal in response to acute stress

BACKGROUND

Thoracic trauma is common, and traffic accident-related traumatic injury can cause acute stress leading to esophageal motility disorders. Interstitial cells of Cajal (ICCs) are regarded as gastrointestinal pacemaker cells.

AIM

This study explored the mechanism underlying changes in lower esophagus ICCs under acute stress conditions.

METHODS

Fifty adult rabbits, randomly divided into one healthy control and four study groups, were subjected to right chest puncture using a Hopkinson bar. Thereafter, one group was immediately subjected to lower esophagectomy, whereas the other three groups were maintained for 24, 48 and 72 h after puncture and subjected to lower esophagectomy. Immunohistochemistry was used to detect ICC distribution, morphology and density, and TUNEL assays were used to determine ICC apoptosis. Enzyme-linked immunosorbent assays (ELISAs) were used to measure cortisol, epinephrine, dopamine, IL-9, cholecystokinin (CCK) and vasoactive intestinal peptide (VIP). Western blotting and RT-PCR were performed to detect changes in SCF/c-kit and nNOS pathways.

RESULTS

After puncture, lung tissue was hemorrhaged, alveoli in puncture areas were destroyed, esophageal pH was decreased, and serum cortisol, epinephrine and dopamine levels increased. ICC numbers increased and apoptotic ICCs decreased in all stress groups after puncture (all p < .01). IL-9, CCK and VIP levels in lower esophagus tissue were increased after puncture (all p < .01). Moreover, SCF/c-kit and nNOS pathways were upregulated in response to stress (all p < .01).

CONCLUSIONS

Acute stress promotes increases in lower esophageal ICCs that might affect esophagus ICC functions and esophageal motility.

Antral Variation of Murine Gastric Pacemaker Cells Informed by Confocal Imaging and Machine Learning Methods

The Interstitial Cells of Cajal (ICC) are specialized gastrointestinal (GI) pacemaker cells that generate and actively propagate electrophysiological events called slow waves. Slow waves regulate the GI motility necessary for digestion. Several functional GI motility disorders have been associated with depletion in the ICC. In this study, a validated Fast Random Forest (FRF) classification method using Trainable WEKA Segmentation for segmenting the networks of ICC was applied to confocal microscopy images of a whole mount tissue from the distal antrum of a mouse stomach (583 × 3,376 × 133 μm³, parcellated into 24 equal image stacks). The FRF model performance was compared to 6 manually segmented subflelds and produced an area under the receiver-operating characteristic (AUROC) of 0.95. Structural variations of ICC network in the longitudinal muscle (ICC-LM) and myenteric plexus (ICC-MP) were quantified. The average volume of ICC-MP was significantly higher than ICC-LM at any point throughout the antral tissue sampled. There was a pronounced decline of up to 80% in ICC-LM (from 3,705 μm³ to 716 μm³) over a distance of 279.3 μm, that eventually diminished towards the distal antrum. However, an inverse relationship was observed in ICC-MP with an overall increase of up to 157% (from 59,100 μm³ to 151,830 μm³) over a distance of approximately 2 mm that proceeds towards the distal antrum.

Ca2+ transients in ICC-MY define the basis for the dominance of the corpus in gastric pacemaking

Myenteric interstitial cells of Cajal (ICC-MY) generate and actively propagate electrical slow waves in the stomach. Slow wave generation and propagation are altered in gastric motor disorders, such as gastroparesis, and the mechanism for the gradient in slow wave frequency that facilitates proximal to distal propagation of slow waves and normal gastric peristalsis is poorly understood.  Slow waves depend upon Ca2+-activated Cl- channels (encoded by Ano1). We characterized Ca2+ signaling in ICC-MY in situ using mice engineered to have cell-specific expression of GCaMP6f in ICC. Ca2+ signaling differed in ICC-MY in corpus and antrum. Localized Ca2+ transients were generated from multiple firing sites and were organized into Ca2+ transient clusters (CTCs). Ca2+ transient refractory periods occurred upon cessation of CTCs, but a relatively higher frequency of Ca2+ transients persisted during the inter-CTC interval in corpus than in antrum ICC-MY. The onset of Ca2+ transients after the refractory period was associated with initiation of the next CTC. Thus, CTCs were initiated at higher frequencies in corpus than in antrum ICC-MY. Initiation and propagation of CTCs (and electrical slow waves) depends upon T-type Ca2+ channels, and durations of CTCs relied upon L-type Ca2+ channels. The durations of CTCs mirrored the durations of slow waves. CTCs and Ca2+ transients between CTCs resulted from release of Ca2+ from intracellular stores and were maintained, in part, by store-operated Ca2+ entry. Our data suggest that Ca2+ release and activation of Ano1 channels both initiate and contribute to the plateau phase of slow waves.

Xiangbinfang granules enhance gastric antrum motility via intramuscular interstitial cells of Cajal in mice

BACKGROUND

Interdigestive migrating motor complexes (MMC) produce periodic contractions in the gastrointestinal tract, but the exact mechanism of action still remains unclear. Intramuscular interstitial cells of Cajal (ICC-IM) participate in gastrointestinal hormone and neuromodulation, but the correlation between ICC-IM and MMC is also unclear. We found that xiangbinfang granules (XBF) mediated the phase III contraction of MMC. Here, the effects of XBF on gastric antrum motility in W/W^v mice and the effects of ICC-IM on gastric antrum MMC are reported.

AIM

To observe the effects of ICC-IM on gastric antrum motility and to establish the mechanism of XBF in promoting gastric antrum motility.

METHODS

The density of c-kit-positive ICC myenteric plexus (ICC-MP) and ICC-IM in the antral muscularis of W/W^v and wild-type (WT) mice was examined by confocal microscopy. The effects of XBF on gastric antrum slow waves in W/W^v and WT mice were recorded by intracellular amplification recording. Micro-strain-gauge force transducers were implanted into the gastric antrum to monitor the MMC and the effect of XBF on gastric antrum motility in conscious W/W^v and WT mice.

RESULTS

In the gastric antrum of W/W^v mice, c-kit immunoreactivity was significantly reduced, and no ICC-IM network was observed. Spontaneous rhythmic slow waves also appeared in the antrum of W/W^v mice, but the amplitude of the antrum slow wave decreased significantly in W/W^v mice (22.62 ± 2.23 mV vs 2.92 ± 0.52 mV, P < 0.0001). MMCs were found in 7 of the 8 WT mice but no complete MMC cycle was found in W/W^v mice. The contractile frequency and amplitude index of the gastric antrum were significantly increased in conscious WT compared to W/W^v mice (frequency, 3.53 ± 0.18 cpm vs 1.28 ± 0.12 cpm; amplitude index, 23014.26 ± 1798.65 mV·20 min vs 3782.16 ± 407.13 mV·20 min; P < 0.0001). XBF depolarized smooth muscle cells of the gastric antrum in WT and W/W^v mice in a dose-dependent manner. Similarly, the gastric antrum motility in WT mice was significantly increased after treatment with XBF 5 mg (P < 0.05). Atropine (0.1 mg/kg) blocked the enhancement of XBF in WT and W/W^v mice completely, while tetrodotoxin (0.05 mg/kg) partially inhibited the enhancement by XBF.

CONCLUSION

ICC-IM participates in the regulation of gastric antrum MMC in mice. XBF induces MMC III-like contractions that enhance gastric antrum motility via ICC-IM in mice.

Continuum Based Bioelectrical Simulations using Structurally Realistic Gastrointestinal Pacemaker Cell Networks

Cellular and tissue level bioelectrical activity was simulated over structurally realistic 3D interstitial cell of Cajal (ICC) networks reconstructed from confocal images of a wild type (WT) mouse model with a normal ICC distribution and a Spry4 knockout (KO) mouse model with a mild ICC hyperplasia. First, the ICC pixels within the confocal images were segmented. Then, the segmented images were visually inspected and the 3D surface mesh of the ICC tissue network was created from the 90 slices spanning the myenteric plexus ICC network. After two additional concentric meshes (representing the non-ICC and tissue bath regions) surrounding the ICC region were added, a 3D tetrahedral volume mesh containing the three regions was reconstructed. The electrical propagation through the tissue network was simulated using the bidomain continuum model. The results showed that the ICC network of the WT mouse had a smaller volume than the KO mouse (0.008 vs 0.012 mm³). The simulated bioelectrical activity for both mice showed an isotropic propagation from the initial activation region. Mean velocities of 4.2±1.5 and 4.1±1.3 mm/s were reported for the WT and KO mice, respectively. The velocity in the x-direction was higher than the y-direction for the WT mouse with a percent difference of 14.8%. On the other hand, the velocity in the y-direction was higher for the KO mouse with a percent difference of 9.5%. For both cases, there was no propagation in the z-direction as all the solution points along the same z-depth were simultaneously activated.

Supervised Machine Learning Segmentation and Quantification of Gastric Pacemaker Cells

Interstitial Cells of Cajal (ICC) are specialized pacemaker cells that generate and actively propagate electrophysiological events called slow waves. Slow waves regulate the motility of the gastrointestinal tract necessary for digesting food. Degradation in the ICC network structure has been qualitatively associated to several gastrointestinal motility disorders. ICC network structure can be obtained using confocal microscopy, but the current limitations in imaging and segmentation techniques have hindered an accurate representation of the networks. In this study, supervised machine learning techniques were applied to extract the ICC networks from 3D confocal microscopy images. The results showed that the Fast Random Forest classification method using Trainable WEKA Segmentation outperformed the Decision Table and Naïve Bayes classification methods in sensitivity, accuracy, and F-measure. Using the Fast Random Forest classifier, 12 gastric antrum tissue blocks were segmented and variations in ICC network thickness, density and process width were quantified for the myenteric plexus ICC network (the primary pacemakers). Our findings demonstrated regional variation in ICC network density and thickness along the circumferential and longitudinal axis of the mouse antrum. An inverse relationship was observed in the distal and proximal antrum for density (proximal: 9.8±4.0% vs distal: 7.6±4.6%) and thickness (proximal: 15±3 μm vs distal: 24±10 μm). Limited variation in ICC process width was observed throughout the antrum (5±1 μm).Clinical Relevance- Detailed quantification of regional ICC structural properties will provide insights into the relationship between ICC structure, slow waves and resultant gut motility. This will improve techniques for the diagnosis and treatment of functional GI motility disorders.

[Role of platelet-derived growth factor receptor α positive cells in purinergic inhibitory nerve-smooth muscle transmission]

Under physiological conditions, the motility of smooth muscle in digestive tract is mainly regulated by enteric nervous system (ENS). However, how neural signal is transmitted to smooth muscle is not fully understood. Autonomic nerve endings in the smooth muscle layer form large number of varicosities which contain neurotransmitters. It was considered that nerve pulses arriving at the varicosities may cause the release of neurotransmitters, which may diffuse to the smooth muscle cells to induce contractile or relaxant responses. Over the past decade, a new understanding of the neurotransmission between ENS and smooth muscle has emerged, which emphasizes the role of a functional syncytium consisting of the interstitial cells of Cajal (ICC), the platelet-derived growth factor receptor α positive (PDGFRα⁺) cells and the smooth muscle cells. Within the syncytium, purine neurotransmitters bind to P2Y1 receptors on PDGFRα⁺ cells, activating small-conductance calcium activated potassium channel (SK3) to hyperpolarize PDGFRα⁺ cells, and thus hyperpolarize smooth muscle cells through gap junction, resulting in relaxation of smooth muscle. In this paper, we review the research progress in the field of inhibitory purinergic neurotransmission in the gastrointestinal tract.

Feasibility of High-Resolution Electrical Mapping for Characterizing Conduction Blocks Created by Gastric Ablation

The interstitial cells of Cajal (ICC) initiate, coordinate and propagate bioelectrical slow wave activity that drives gastric motility. In the healthy human stomach, slow wave activity is highly organized. Gastric motility disorders are associated with dysrhythmias. While ablation is widely used to treat cardiac dysrhythmias, this approach has yet to be trialed in the stomach. In this study, radiofrequency (RF) ablation was applied in pig stomachs in vivo to create targeted electrical conduction blocks. Ablations were performed at temperature control mode (55-70°C), and resultant conduction blocks were identified and verified using high-resolution electrical mapping. Termination of slow wave propagation at ablation sites was confirmed by a decrease in extracellular slow wave amplitude from 1.7 ± 0.2 mV to an undetectable amplitude, as well as spatiotemporal pattern analysis of conduction blocks. The use of high-resolution electrical mapping can now be employed to investigate ablation as a potential therapy for gastric dysrhythmias in motility disorders.

A Pipeline for the Registration of Calcium Transient Data to Structural Networks of the Interstitial Cells of Cajal

Interstitial cells of Cajal (ICC) generate electrical pacemaker activity in the gastrointestinal (GI) tract known as slow waves, which regulate GI motility. ICC express both the Kit receptor tyrosine kinase protein and a Ca²⁺-activated Cl^--channel, encoded by the anoctamin1 (Ano1) protein, which is an essential contributor to the Ca²⁺ cycling of ICC and slow wave pacemaking. Recent dye-loading imaging studies have demonstrated Ca²⁺ transients in ICC in isolated tissue preparations. The main aim of this study was to develop a method that allows Ca²⁺ transients to be registered to structural ICC network data. Confocal image stacks of ICC labeled for Kit or Ano1 and Ca²⁺ recording data were processed using a thresholding protocol. The Ca²⁺ transients were then registered to the ICC structural network. First, a general idea of the placement was found by mapping the field-of-view of the Ca²⁺ transient data to the distorted tissue that contained the ICC network image. The errors in the registration were then corrected for by warping the internal Ca²⁺ transient field according to the structural network. In data sets from tissues with induced, targeted knockdown of Ano1 expression in a subset of ICC, agreement between the Ca²⁺ transient data and structural network was 68 ± 10%. This level of agreement allowed selective extraction of Ca²⁺ data from Ano1-positive (Ano1+) and Ano1-negative (Ano1-) ICC. In the future, this technique will allow investigation into the functional properties of ICC in relation to the level of knockdown of specific ICC associated proteins.

Tissue specific simulations of interstitial cells of cajal networks using unstructured meshes

Gastrointestinal motility is facilitated by specialized pacemaker cells called Interstitial Cells of Cajal (ICC). ICC play a critical role in coordinating normal motility and its degradation in the gastrointestinal tract is associated with many functional motility disorders. Nonetheless, the degree of degradation and associated clinical impact remains unclear. Continuum modeling frameworks offers a virtual mean to simulate the electrical activity, and analyze the ICC activity in both normal and diseased states. Confocal images of the ICC networks were obtained from the intestine of normal mice. In this study, a new approach is presented where meshes of ICC networks were generated using a Delaunay triangulation and used to solve finite-element based reaction-diffusion equations describing gastrointestinal electrophysiology. The electrical activity was simulated on the ICC network and solutions were compared to those of a regular mesh based on individual pixel locations. The simulation results showed the proposed approach to be approximately 80% more efficient than a pixel-based mesh. The difference in activation time for the entire network between the different methods was observed to be around 4% (about 20 ms). The proposed approach will enable efficient examination of the ICC slow wave activity in larger networks and for longer temporal duration that has been previously impossible. This will provide valuable insights relating ICC degradation to gastrointestinal motility disorders.

A framework for simulating gastric electrical propagation in confocal microscopy derived geometries

Interstitial Cells of Cajal (ICC) initiate and actively propagate electrical events in the gastrointestinal tract known as slow-waves. The slow-waves coordinate the contraction of the gastrointestinal tract necessary for breakdown and mixing of ingested food. Degradation of the ICC numbers has been linked to several gastrointestinal motility disorders. However, limitations in imaging techniques and techniques for the quantification of ICC network structure have hindered our understanding of these disorders. We evaluated different machine learning techniques to segment ICC networks imaged using confocal microscopy. The accuracy the segmented networks were then quantified and compared using numerical metrics. Structurally realistic finite element meshes were constructed and used to simulate the propagation of electrical activation over the tissue blocks. The presented framework provides a system to quantify the structure and function of an ICC tissue sample. These methods are also applicable to other biological tissues and networks.

A mathematical model of the effects of anoctamin-1 loss on intestinal slow wave entrainment

The interstitial cells of Cajal (ICC) generate electrophysiological events called slow waves that regulate the motility of the gastrointestinal (GI) tract. Recent studies have demonstrated that the Ca²⁺-activated Cl^- -channel, encoded by the anoctamin1 (Ano1) protein, has a major role in regulating intestinal slow waves and motility. The main aim of this study was to develop a multi-scale mathematical model capable of simulating both normal slow wave entrainment and the effects of Ano1 knockout (KO) on the normal activity. A biophysically-based cell model was adapted to simulate the effects of Ano1 KO at the cellular level. A 10mm one-dimensional (1D) model was then developed to simulate entrained intestinal slow wave propagation. Cellular KO at levels of 100% and 20% were applied to a varying-sized middle region of the 1D model. The main finding was that the level of loss of entrainment increased as both cellular and spatial Ano1 KO levels increased, mostly manifesting as ectopic activation. In the future, this model will be extended and used in combination with Ca²⁺ -imaging data to quantitatively investigate the effects of Ano1 loss in ICC.

Many parts make a whole: Calcium transients sum for slow waves

New JGP study shows how calcium events drive long intestinal slow wave plateaus.

New JGP study shows how calcium events drive long intestinal slow wave plateaus.

[Experimental study of Bisacodyl in the treatment of slow transit constipation model rats]

OBJECTIVE

To explore the efficacy and the mechanism of Bisacodyl in treating slow transit constipation model rats.

METHODS

A total of 30 healthy rats were enrolled. Twenty rats received intragastric diphenoxylate to develop slow transit constipation (STC) model, and 10 untreated rats were set as blank control. STC rats were subdivided into two groups: STC Bisacodyl group (fed with Bisacodyl) and STC control group (common feed). Body weight, number and dry weight of faeces, and intestinal transit time were compared among 3 groups. Interstitial cells of Cajal(ICC) and c-Kit protein expression were measured by immunohistochemical staining. Restults Compared to blank control rats, at 100-day of receiving intragastric diphenoxylate, above 20 rats presented the decrease of body weight and feces number, the increase of dry weight of faeces, and the delay of intestinal transit time, indicating the successful establishment of STC rat model. One month after feeding, compared to STC control group, STC Bisacodyl grap had an increased feces number[(36.6±6.8) pill/day vs. (26.8±6.0) pill/day], decreased dry weight of feces [(150.6±10.5) mg/pill vs. (171.6±16.3) mg/pill] and shortened intestinal transit time [(416.9±50.6) minutes vs. (495.3±66.8) minutes], and the differences were statistically significant(all P<0.05). Dissolution of ICC basement membrane, damage of connection between ICC and surrounding cells, and atrophy of ICC nucleus structure were found in STC control rats. ICC (8.20±1.92 per field] and c-Kit expression (12.68%±2.59% ) in STC control rats were significantly lower than those in blank control rats(36.00±6.25 per field and 71.50 %±8.27%) (P=0.000). Compared to STC control group, the connection between ICC and surrounding cells enhanced obviously, ICC (18.80±3.70 per field) and c-Kit expression (45.91%±6.80%) were significantly higher in STC Bisacodyl group (all P=0.000).

CONCLUSION

Bisacodyl treatment can relieve STC symptoms, which may be associated with increased ICC number and c-Kit protein expression.

[Physiological and pathophysiological meanings of gastrointestinal smooth muscle motor unit SIP syncytium]

Gastrointestinal smooth muscle layer contains two kinds of interstitial cells with special differentiation, i.e., interstitial cells of Cajal (ICC) and platelet-derived growth factor receptor α-positive (PDGFRα⁺) cells. The ICC and PDGFRα⁺ cells contact with smooth muscle cells (SMCs) by gap junctions and regulate contractive function of the SMCs. Therefore, these three kinds of cells constitute a functional syncytium, i.e., the SMC, ICC and PDGFRα⁺ cells syncytium (SIP syncytium). Various neurotransmitters, humoral factors, endogenous bioactive molecules, as well as drugs regulate gastrointestinal motility through the SIP syncytium. In this review, we introduce the concept of SIP syncytium and summarize functions of the syncytium, as well as its physiological and pathological significances.

Interstitial cells of Cajal - systematic review

This paper reviews the distribution of interstitial cells of Cajal (ICC) in the human gastro-intestinal (GI) tract, based on ultrastructural and immunohistochemical evidence. The distribution and morphology of ICC at each level of the normal GI tracts is addressed from the perspective of their functional significance. Alterations of ICC reported in as well as in GI stromal tumours are reviewed, with emphasis on the place of ICC in the pathophysiology of disease.

Determining the efficient inter-electrode distance for high-resolution mapping using a mathematical model of human gastric dysrhythmias

Motility of the stomach is in part coordinated by an electrophysiological event called slow waves, which are generated by pacemaker cells called the interstitial cells of Cajal (ICC). In functional motility disorders, which can be associated with a reduction of ICC, dynamic slow wave dysrhythmias can occur. In recent years, high-resolution (HR) mapping techniques have been applied to describe both normal and dysrhythmic slow wave patterns. The main aim of this study was to inform gastric HR mapping array design by determining the efficient inter-electrode distance required to accurately capture normal and dysrhythmic gastric slow wave activity. A two-dimensional mathematical model was used to simulate normal activity and four types of reported slow wave dysrhythmias in human patients: ectopic activation, retrograde propagation, slow conduction, conduction block. For each case, the simulated data were re-sampled at 4, 6, 10, 12, 20 and 30mm inter-electrode distances. The accuracy of each distance was compared to a reference set sampled at 2mm inter-electrode distance, in terms of accuracy of velocity, using an ANOVA. Manual groupings were also conducted to test the ability of the human markers to distinguish separate cycles of slow waves as inter-electrode distance increases. The largest interelectrode distance for human gastric slow wave analysis, which produced both accurate grouping and velocity, was 10mm (CI [0.3 2.4]mms(-1); p<;0.05). Therefore an inter-electrode distance of less than 10mm was required to accurately describe the types of baseline and dysrhythmic activities reported in this study. However, it is likely that more spatially complex dysrhythmias, such as re-entry, may require finer inter-electrode distances.

[Establishment of rat slow transit constipation model by selective chemical ablation of the enteric plexus]

OBJECTIVE

To establish an innovative rat model of slow transit constipation by selective chemical ablation of the colon enteric plexus.

METHODS

Sprague Dawley rats, 5-6 weeks old, were randomly divided into normal control group, sham operation group, treatment group I, II, III, IIII. The normal control group did not receive treatment. Rats in the sham operation group and the treatment groups received abdominal operation under anesthesia, and the gauze containing 0.9% normal saline, 0.05%, 0.1%, 0.25%, 0.5% benzalkonium chloride (BAC) was applied into colon for 30 minutes. Two weeks after operation, the number of feces, fecal dry weight in 24 h and gastrointestinal transit time were recorded, then hematoxylin-eosin (HE) staining, immunohistochemistry, ELISA were used for the evaluation of colonic pathology, enteric plexus, Interstitial cells of Cajal and neurotransmitters 5-hydroxytryptamine(5-HT).

RESULTS

Compared to the normal control group and the sham operation group, the gastrointestinal transit time was significantly prolonged and fecal dry weight was lower in the treatment group II, III (all P<0.05). HE and immunohistochemical staining showed varying degrees of pathological changes in the treatment groups and in line with the pathological changes of slow transit constipation. 5-HT concentration reduced significantly in treatment group III compared to other groups (P<0.01).

CONCLUSION

The animal model of STC is successfully established by applying 0.25% BAC selective chemical ablation of the colon enteric plexus. This model is simple, stable, and is more in line with pathological changes of slow transit constipation.

[Effect of intestinal resection on hydrogen sulfide biosynthesis and the damage of Cajal interstitial cells]

OBJECTIVE

To investigate the effect of intestinal resection on hydrogen sulfide (H2S) biosynthesis and interstitial cells of Cajal(ICC) in mice.

METHODS

After intestinal resection mouse model was established, the activity of MPO in the proximal anastomosis intestinal tissue were detected. Sensitive sulphur electrode assay was applied to measure the H2S level. RT-PCR technique was employed to investigate the mRNA expression of the endogenous H2S biosynthesis enzymes, cystathionine-b-synthase (CBS) and cystathionine-c-lyase (CSE). Immunofluorescence staining was used to detect the expression of c-kit in order to calculate the area of ICC.

RESULTS

The mRNA expression of CSE was detected in the small intestine tissue of mice, while no CBS mRNA was found. The mRNA expression of CSE in proximal anastomotic stoma increased in time-dependent manner in the model group. CSE mRNA expression began to increase 1 hour after operation, reached the peak at 6th hour, then decreased gradually, and was similar to the control group at postoperative 24th hour. Compared to the model group, in the intestinal tissues of proximal 3 cm to anastomotic stoma, the mRNA expression of CSE (1.16 ± 0.18 vs. 1.63 ± 0.13, P<0.05), the activity of MPO [(0.54 ± 0.07) U/g vs. (0.83 ± 0.09) U/g, P<0.05], the H2S level [(36.1 ± 6.1) nmol/mg vs. (5.3 ± 5.6) nmol/mg, P<0.05] were significantly reduced in the PPG group. Meanwhile, average percentage of positive ICC area in the PPG groups was significantly higher [(2.26 ± 0.19)% vs. (1.65 ± 0.24)%, P<0.05].

CONCLUSIONS

Inflammatory reaction in muscular layer induced by intestinal resection up-regulates the mRNA expression of CSE proximal to anastomotic stoma, generates excess H2S to damage ICC leading to intestinal motor dysfunction. Preoperative inhibition of endogenous H2S generation may protect the ICC.

Interstitial cell of Cajal loss correlates with the degree of inflammation in the human appendix and reverses after inflammation

BACKGROUND

Normal gut motility relies on the complex interaction between the interstitial cell of Cajal (ICC) and the enteric nerve networks. Inflammation of the gastrointestinal tract adversely affects both ICC and enteric nerves. We aimed to determine the distribution of ICC and nerve networks in patients with appendicitis.

METHODS

Specimens from controls and patients with appendicitis were examined with immunohistochemistry (c-Kit for ICC, beta III tubulin [Tuj-1] and neuronal nitric oxide synthase [histochemical diaphorase] for nitrergic neurons) and electron microscopy (EM). Data were quantified using image analysis.

RESULTS

We found a profound decrease in c-Kit immunoreactivity (c-Kit IR) in the advanced inflammatory stages of appendicitis, which correlated with the severity of inflammation. Electron microscopy confirmed ultrastructural injury in both ICC and nerve fiber networks during acute inflammation. After the inflammation resolved, interval appendices displayed a recovery in ICC c-Kit IR to control levels and normal ultrastructure. The neuronal network also displayed ultrastructural recovery; however, neuronal nitric oxide synthase activity did not recover.

CONCLUSIONS

Severe inflammation results in significant ultrastructural damage of nerves and ICC networks in appendicitis. The loss of c-Kit IR is likely due to impaired ICC cytophysiology because ICC was still present under EM. After resolution of acute inflammation, ICC recovers their normal ultrastructure and c-Kit IR.

Cajal beyond the gut: interstitial cells in the urinary system--towards general regulatory mechanisms of smooth muscle contractility?

Interstitial cells of Cajal (ICC), similar to GI pacemakers have been identified throughout the urinary system. Although each part of the system serves a different function, ranging from peristalsis of the ureters, storage of urine by the bladder, and a sphincteric action by the urethra, they share a common mechanism in being able to generate phasic myogenic contractions. Even the urethra, often considered to be a 'tonic' smooth muscle, achieves an apparently sustained contraction by averaging numerous small asynchronous 'phasic' contractions. This activity can occur in the absence of any neural input, implying the presence of an intrinsic pacemaker. Intracellular microelectrode recordings from urethral muscle strips reveal electrical slow waves similar to those of the GI tract. To study this further, we isolated single cells from rabbit urethra and found not only smooth muscle cells (SMC), but a second cell type comprising -10% of the total. The latter cells were branched and non-contractile and closely resembled intestinal ICC. Electrophyiological studies revealed that, while the isolated smooth muscle cells were electrically quiescent, the 'ICC' fired electrical slow waves similar to those observed in the whole tissue. The basis of this difference was the presence of a large pacemaker current involving the activation of calcium-activated Cl channels by spontaneous intracellular Ca2+ waves. These, in turn, have been shown to be modulated by neurotransmitters such as nitric oxide, noradrenaline and ATP, thus providing a possible mechanism whereby neural regulation of the urethra, as well as spontaneous tone, may be mediated via ICC.