Organization and development of pacemaker of gastrointestinal tract

Rhythmical depolarization and automatic contraction of smooth muscle of the gastrointestinal tract are consequences of pacemaker activity of c-Kit-immunoreactive cells of mesenchymal origin--interstitial Cajal cells (CC) that have a peculiar mechanism of intracellular Ca2+ exchange controlled by mitochondria. The intermuscular layer cells (ICC-MY) generate pacemaker potentials. They produce depolarization that is enhanced by unitary potentials evoked by the intermuscular population--ICC-IM. Summation of unitary potentials in time of the pacemaker ones leads to creation of the second potentials of slow waves--plateau-potentials. Due to the presence of synapse-like structures, ICC serve messengers of transmission of signals of the enteral nervous system to muscle. Long processes and tight intercellular contacts similar to the cleft ones provide transduction and coordination of excitation in the intestinal musculature. Electrical rhythmicity appears in the enteric musculature at the prenatal period in parallel with structural and functional ICC maturation, but formation of mature rhythm parameters occurs in postnatal ontogenesis. Features of similarity and differences in organization of control of heart and the gastrointestinal tract musculature by pacemakers are considered.     

Hesperidin depolarizes the pacemaker potentials through 5-HT4 receptor in murine small intestinal interstitial cells of Cajal

ABSTRACT

Hesperidin, a citrus flavonoid, can exert numerous beneficial effects on human health. Interstitial cells of Cajal (ICC) are pacemaker cells in the gastrointestinal (GI) tract. In the present study, we investigated potential effects of hesperidin on pacemaker potential of ICC in murine small intestine and GI motility. A whole-cell patch-clamp configuration was used to record pacemaker potential in ICC, and GI motility was investigated in vivo by recording gastric emptying (GE) and intestinal transit rate (ITR). Hesperidin depolarized pacemaker potentials of ICC in a dose-dependent manner. Pre-treatment with methoctramine or 4-DAMP did not inhibit hesperidin-induced pacemaker potential depolarization. Neither a 5-HT₃ receptor antagonist (Y25130) nor a 5-HT₇ receptor antagonist (SB269970) reduced the effect of hesperidin on ICC pacemaker potential, whereas the 5-HT₄ receptor antagonist RS39604 was found to inhibit this effect. In the presence of GDP–β–S, hesperidin-induced pacemaker potential depolarization was inhibited. Moreover, in the presence of U73122 and calphostin C, hesperidin did not depolarize pacemaker potentials. Furthermore, hesperidin accelerated GE and ITR in vivo. These results imply that hesperidin depolarized ICC pacemaker potential via 5-HT₄ receptors, G protein, and PLC/PKC dependent pathways and that it increased GI motility. Therefore, hesperidin may be a promising novel drug to regulate GI motility.     

Pacemaker potentials generated by interstitial cells of Cajal in the murine intestine

Pacemaker potentials were recorded in situ from myenteric interstitial cells of Cajal (ICC-MY) in the murine small intestine. The nature of the two components of pacemaker potentials (upstroke and plateau) were investigated and compared with slow waves recorded from circular muscle cells. Pacemaker potentials and slow waves were not blocked by nifedipine (3 µM). In the presence of nifedipine, mibefradil, a voltage-dependent Ca²⁺ channel blocker, reduced the amplitude, frequency, and rate of rise of upstroke depolarization (dV/dt_max) of pacemaker potentials and slow waves in a dose-dependent manner (1–30 µM). Mibefradil (30 µM) changed the pattern of pacemaker potentials from rapidly rising, high-frequency events to slowly depolarizing, low-frequency events with considerable membrane noise (unitary potentials) between pacemaker potentials. Caffeine (3 mM) abolished pacemaker potentials in the presence of mibefradil. Pinacidil (10 µM), an ATP-sensitive K⁺ channel opener, hyperpolarized ICC-MY and increased the amplitude and dV/dt_max without affecting frequency. Pinacidil hyperpolarized smooth muscle cells and attenuated the amplitude and dV/dt_max of slow waves without affecting frequency. The effects of pinacidil were blocked by glibenclamide (10 µM). These data suggest that slow waves are electrotonic potentials driven by pacemaker potentials. The upstroke component of pacemaker potentials is due to activation of dihydropyridine-resistant Ca²⁺ channels, and this depolarization entrains pacemaker activity to create the plateau potential. The plateau potential may be due to summation of unitary potentials generated by individual or small groups of pacemaker units in ICC-MY. Entrainment of unitary potentials appears to depend on Ca²⁺ entry during upstroke depolarization. pacemaker activity; slow waves; gastrointestinal motility; calcium channel     

Vasoactive intestinal polypeptide inhibits pacemaker activity via the nitric oxide-cGMP-protein kinase G pathway in the interstitial cells of Cajal of the murine small intestine

Interstitial cells of Cajal (ICCs) are pacemaker cells that activate the periodic spontaneous depolarization (pacemaker potentials) responsible for the production of slow waves in gastrointestinal smooth muscle. The effects of vasoactive intestinal polypeptide (VIP) on the pacemaker potentials in cultured ICCs from murine small intestine were investigated by whole-cell patch-clamp techniques. Addition of VIP (50 nM-1 microM) decreased the amplitude of pacemaker potentials and depolarized resting membrane potentials. To examine the type of receptors involved in ICC, we examined the effects of the VIP1 agonist and found that it had no effect on pacemaker potentials. Pretreatment with VIP1 antagonist (1 microM) for 10 min also did not block the VIP (50 nM)-induced effects. On the other hand exposure to 1H-(1,2,4)oxadiazolo(4,3-A)quinoxalin- 1-one (ODQ, 100 microM), an inhibitor of guanylate cyclase, prevented VIP inhibition of pacemaker potentials. Similarly KT-5823 (1 microM) or RP-8-CPT-cGMPS (10 microM), inhibitors of protein kinase G (PKG) blocked the effect of VIP (50 nM) on pacemaker potentials as did N-nitro-L-arginine (L-NA, 100 mM), a non-selective nitric oxide synthase (NOS) inhibitor. These results imply that the inhibition of pacemaker activity by VIP depends on the NO-cGMP-PKG pathway.     

Effects of transient receptor potential channel blockers on pacemaker activity in interstitial cells of Cajal from mouse small intestine

The interstitial cells of Cajal (ICCs) are pacemakers in the gastrointestinal tract and transient receptor potential melastatin type 7 (TRPM7) is a candidate for pacemaker channels. The effect of the 5-lipoxygenase (5-LOX) inhibitors NDGA, AA861, MK886 and zileuton on pacemaking activity of ICCs was examined using the whole cell patch clamp technique. NDGA and AA861 decreased the amplitude of pacemaker potentials in ICC clusters, but the resting membrane potentials displayed little change, respectively. Also, perfusing NDGA and AA861 into the bath reduced both inward current and outward current in TRPM7-like current in single ICC, respectively. But, they had no effects on Ca²⁺ activated Cl⁻ currents. The 5-LOX inhibitors MK886 and zileuton were, however, ineffective in pacemaker potentials in ICC clusters and in TRPM7-like current in single ICC, respectively. A specific TRPC3 inhibitor, pyrazole compound (Pyr3), and a specific TRPM4 inhibitor, 9-phenanthrol, had no effects in pacemaker potentials in ICC clusters and in TRPM7-like current in single ICC. These results suggest that, among the tested 5-LOX inhibitors, NDGA and AA861 modulate the pacemaker activities of the ICCs, and that the TRPM7 channel can affect intestinal motility.     

Sphingosine and FTY720 modulate pacemaking activity in interstitial cells of Cajal from mouse small intestine

Interstitial cells of Cajal (ICCs) are the pacemakers of the gastrointestinal tract, and transient receptor potential melastatin type 7 (TRPM7) and Ca²⁺ activated Cl⁻ channels (ANO1) are candidate the generators of pacemaker potentials in ICCs. The effects of D-erythro-sphingosine (SPH) and structural analogues of SPH, that is, N,N-dimethyl-Derythro-sphingosine (N,N-DMS), FTY720, and FTY720-P on the pacemaking activities of ICCs were examined using the whole cell patch clamp technique. SPH, N,N-DMS, and FTY720 decreased the amplitudes of pacemaker potentials in ICC clusters, but resting membrane potentials displayed little change. Also, perfusing SPH, N,N-DMS, or FTY720 in the bath reduced both inward and outward TRPM7-like currents in single ICCs, and inhibited ANO1 currents. The another structural analogue of SPH, FTY720-P was ineffective at the pacemaker potentials in ICC clusters and the TRPM7-like currents in single ICCs. Furthermore, FTY720- P had no effect on ANO1. These results suggest that SPH, N,N-DMS, and FTY720 modulate the pacemaker activities of ICCs, and that TRPM7 and ANO1 channels affect intestinal motility.     

Effects of ginsenoside on pacemaker potentials of cultured interstitial cells of Cajal clusters from the small intestine of mice

Ginsenoside, one of the active ingredients of Panax ginseng, has a variety of physiological and pharmacological actions in various organs. However, little is known about the effects of ginsenosides on gastrointestinal (GI) motility. We studied the modulation of pacemaker potentials by ginsenoside in the interstitial cells of Cajal (ICCs) using the whole-cell patch clamp technique in the current clamp mode. Among ginsenosides, we investigated the effects of ginsenoside Rb1, Rg3 and Rf. While externally applied Rb1 and Rg3 had no effects on pacemaker potentials, Rf caused membrane depolarization. The application of flufenamic acid or niflumic acid abolished the generation of pacemaker potentials and inhibited the Rf-induced membrane depolarization. Membrane depolarization induced by Rf was not inhibited by intracellular application of guanosine 5′-[β-thio]diphosphate trilithium salt. Pretreatment with a Ca²⁺-free solution, thapsigargin, a Ca²⁺-ATPase inhibitor of the endoplasmic reticulum, U-73122, a phospholipase C inhibitor, or 2-APB, an IP3 receptor inhibitor, abolished the generation of pacemaker potentials and suppressed Rfinduced actions. However, treatment with chelerythrine and calphostin C, protein kinase C inhibitors, did not block Rf-induced effects on pacemaker potentials. These results suggest that ginsenoside Rf modulates the pacemaker activities of ICCs and therby regulates intestinal motility.     

Role of Interstitial Cells of Cajal and their relationship with the enteric nervous system.

The term 'Interstitial cells of Cajal' (ICC) designates several groups of mesenchymal cells present along the gastro-intestinal tract (GI), in close association with smooth muscle cells and elements of the enteric nervous system (ENS). For years, transmission electron microscopy (TEM) has been the only reliable tool to study ICC. Whilst TEM remains the golden standard for identification of ICC, the observation that the tyrosine kinase receptor c-kit plays a crucial role in their development recently resulted in numerous immunohistochemical studies and also led to a better characterization of their roles. ICC form extensive networks of electrically coupled cells and certain groups of ICC are currently regarded as the source of the spontaneous slow waves of the gut musculature (pacemaker cells). Other ICC appear to be involved in the transduction of the relaxation of smooth muscle triggered by nitric oxide. Abnormal distribution of ICC has been reported in several human diseases and abnormal functioning of ICC might actually be involved in many disorders of GI transit. This review addresses (1) the morphology and relationships of ICC along the GI tract in man and mouse, mainly based on data from immunohistochemistry and confocal microscopy, (2) the emerging role of ICC in the pathophysiology of human diseases, like infantile hypertrophic pyloric stenosis (a common disorder with a dysfunction of the pyloric sphincter), Hirschsprung's disease (aganglion-osis coli) and intestinal pseudo-obstruction, (3) developmental issues, (4) recent reports suggesting a possible link between ICC and gastrointestinal stromal tumors.     

Neurotensin modulates pacemaker activity in interstitial cells of Cajal from the mouse small intestine

Neurotensin, a tridecapeptide localized in the gut to discrete enteroendocrine cells of the small bowel mucosa, is a hormone that plays an important role in gastrointestinal secretion, growth, and motility. Neurotensin has inhibitory and excitatory effects on peristaltic activity and produces contractile and relaxant responses in intestinal smooth muscle. Our objective in this study is to investigate the effects of neurotensin in small intestinal interstitial cells of Cajal (ICC) and elucidate the mechanism. To determine the electrophysiological effects of neurotensin on ICC, whole-cell patch clamp recordings were performed in cultured ICC from the small intestine. Exposure to neurotensin depolarized the membrane of pacemaker cells and produced tonic inward pacemaker currents. Only neurotensin receptor1 was identified when RT-PCR and immunocytochemistry were performed with mRNA isolated from small intestinal ICC and c-Kit positive cells. Neurotensin-induced tonic inward pacemaker currents were blocked by external Na⁺- free solution and in the presence of flufenamic acid, an inhibitor of non-selective cation channels. Furthermore, neurotensin-induced action is blocked either by treatment with {"type":"entrez-nucleotide","attrs":{"text":"U73122","term_id":"4098075","term_text":"U73122"}}U73122, a phospholipase C inhibitor, or thapsigargin, a Ca²⁺-ATPase inhibitor in ICC. We found that neurotensin increased spontaneous intracellular Ca²⁺ oscillations as seen with fluo4/AM recording. These results suggest that neurotensin modulates pacemaker currents via the activation of non-selective cation channels by intracellular Ca²⁺-release through neurotensin receptor1.     

Induction of pacemaker currents by DA-9701, a prokinetic agent, in interstitial cells of Cajal from murine small intestine

The interstitial cells of Cajal (ICC) are pacemaking cells required for gastrointestinal motility. The possibility of whether DA-9701, a novel prokinetic agent formulated with Pharbitis Semen and Corydalis Tuber, modulates pacemaker activities in the ICC was tested using the whole cell patch clamp technique. DA-9701 produced membrane depolarization and increased tonic inward pacemaker currents in the voltage-clamp mode. The application of flufenamic acid, a non-selective cation channel blocker, but not niflumic acid, abolished the generation of pacemaker currents induced by DA-9701. Pretreatment with a Ca²⁺-free solution and thapsigargin, a Ca²⁺-ATPase inhibitor in the endoplasmic reticulum, abolished the generation of pacemaker currents. In addition, the tonic inward currents were inhibited by U-73122, an active phospholipase C inhibitor, but not by GDP-β-S, which permanently binds G-binding proteins. Furthermore, the protein kinase C inhibitors, chelerythrine and calphostin C, did not block the DA-9701-induced pacemaker currents. These results suggest that DA-9701 might affect gastrointestinal motility by the modulation of pacemaker activity in the ICC, and the activation is associated with the non-selective cationic channels via external Ca²⁺ influx, phospholipase C activation, and Ca²⁺ release from internal storage in a G protein-independent and protein kinase C-independent manner.     

Ether-a-go-go-related gene 3 is the main candidate for the E-4031-sensitive potassium current in the pacemaker interstitial cells of Cajal

The interstitial cells of Cajal (ICC), as pacemaker cells of the gut, contribute to rhythmic peristalsis and muscle excitability through initiation of slow-wave activity, which subsequently actively propagates into the musculature. An E-4031-sensitive K(+) current makes a critical contribution to membrane potential in ICC. This study provides novel features of this current in ICC in physiological solutions and seeks to identify the channel isoform. In situ hybridization and Kit immunohistochemistry were combined to assess ether-a-go-go-related gene (ERG) mRNA expression in ICC in mouse jejunum, while the translated message was assessed by immunofluorescence colocalization of ERG and Kit proteins. E-4031-sensitive currents in cultured ICC were studied by the whole cell patch-clamp method, with physiological K(+) concentration in the bath and the pipette. In situ hybridization combined with Kit immunohistochemistry detected m-erg1 and m-erg3, but not m-erg2, mRNA in ICC. ERG3 protein was colocalized with Kit-immunoreactive ICC in jejunum sections, but ERG1 protein was visualized only in the smooth muscle cells. At physiological K(+) concentration, the E-4031-sensitive outward current in ICC was different from its counterpart in cardiac and gut smooth muscle cells. In particular, inactivation upon depolarization and recovery from inactivation by hyperpolarization were modest in ICC. In summary, the E-4031-sensitive currents influence the kinetics of the pacemaker activity in ICC and contribute to maintenance of the resting membrane potential in smooth muscle cells, which together constitute a marked effect on tissue excitability. Whereas this current is mediated by ERG1 in smooth muscle, it is primarily mediated by ERG3 in ICC.     

Caja1间质细胞与慢性假性结肠肠梗阻关系的研究进展

Cajal间质细胞（interstitial cells of cajal,ICC）主要分布在胃肠道平滑肌细胞与神经纤维之间,是一类特殊的间质细胞,它是胃肠运动的起搏细胞,具有产生、传导慢波,调节胃肠道平滑肌运动的功能。而慢性假性肠梗阻是由于胃肠神经抑制,毒素刺激或肠壁平滑肌本身病变,导致的肠壁肌肉运动功能减弱,临床上具有肠梗阻的症状和体征,但无肠内外机械性肠梗阻因素存在,故又称动力性肠梗阻。按病程有急性和慢性之分,麻痹性肠梗阻和痉挛性肠梗阻属于急性假性肠梗阻,深入研究Caja1间质细胞,对进一步认识胃肠运动的生理及胃肠动力疾病的发生机制有重要意义。     

Pacemaker activity and inhibitory neurotransmission in the colon of Ws/Ws mutant rats

The aim of this study was to characterize the pacemaker activity and inhibitory neurotransmission in the colon of Ws/Ws mutant rats, which harbor a mutation in the c-kit gene that affects development of interstitial cells of Cajal (ICC). In Ws/Ws rats, the density of KIT-positive cells was markedly reduced. Wild-type, but not Ws/Ws, rats showed low- and high-frequency cyclic depolarization that were associated with highly regular myogenic motor patterns at the same frequencies. In Ws/Ws rats, irregular patterns of action potentials triggered irregular muscle contractions occurring within a bandwidth of 10-20 cycles/min. Spontaneous activity of nitrergic nerves caused sustained inhibition of muscle activity in both wild-type (+/+) and Ws/Ws rats. Electrical field stimulation of enteric nerves, after blockade of cholinergic and adrenergic activity, elicited inhibition of mechanical activity and biphasic inhibitory junction potentials both in wild-type and Ws/Ws rats. Apamin-sensitive, likely purinergic, inhibitory innervation was not affected by loss of ICC. Variable presence of nitrergic innervation likely reflects the presence of direct nitrergic innervation to smooth muscle cells as well as indirect innervation via ICC. In summary, loss of ICC markedly affects pacemaker and motor activities of the rat colon. Inhibitory innervation is largely maintained but nitrergic innervation is reduced possibly related to the loss of ICC-mediated relaxation.     

Biophysically Based Mathematical Modeling of Interstitial Cells of Cajal Slow Wave Activity Generated from a Discrete Unitary Potential Basis

Spontaneously rhythmic pacemaker activity produced by interstitial cells of Cajal (ICC) is the result of the entrainment of unitary potential depolarizations generated at intracellular sites termed pacemaker units. In this study, we present a mathematical modeling framework that quantitatively represents the transmembrane ion flows and intracellular Ca²⁺ dynamics from a single ICC operating over the physiological membrane potential range. The mathematical model presented here extends our recently developed biophysically based pacemaker unit modeling framework by including mechanisms necessary for coordinating unitary potential events, such as a T-Type Ca²⁺ current, V_m-dependent K⁺ currents, and global Ca²⁺ diffusion. Model simulations produce spontaneously rhythmic slow wave depolarizations with an amplitude of 65 mV at a frequency of 17.4 cpm. Our model predicts that activity at the spatial scale of the pacemaker unit is fundamental for ICC slow wave generation, and Ca²⁺ influx from activation of the T-Type Ca²⁺ current is required for unitary potential entrainment. These results suggest that intracellular Ca²⁺ levels, particularly in the region local to the mitochondria and endoplasmic reticulum, significantly influence pacing frequency and synchronization of pacemaker unit discharge. Moreover, numerical investigations show that our ICC model is capable of qualitatively replicating a wide range of experimental observations.     

The effects of mitochondrial inhibitors on Ca2+ signalling and electrical conductances required for pacemaking in interstitial cells of Cajal in the mouse small intestine

Interstitial cells of Cajal (ICC-MY) are pacemakers that generate and propagate electrical slow waves in gastrointestinal (GI) muscles. Slow waves appear to be generated by the release of Ca²⁺ from intracellular stores and activation of Ca²⁺-activated Cl⁻ channels (Ano1). Conduction of slow waves to smooth muscle cells coordinates rhythmic contractions. Mitochondrial Ca²⁺ handling is currently thought to be critical for ICC pacemaking. Protonophores, inhibitors of the electron transport chain (FCCP, CCCP or antimycin) or mitochondrial Na⁺/Ca²⁺ exchange blockers inhibited slow waves in several GI muscles. Here we utilized Ca²⁺ imaging of ICC in small intestinal muscles in situ to determine the effects of mitochondrial drugs on Ca²⁺ transients in ICC. Muscles were obtained from mice expressing a genetically encoded Ca²⁺ indicator (GCaMP3) in ICC. FCCP, CCCP, antimycin, a uniporter blocker, Ru360, and a mitochondrial Na⁺/Ca²⁺ exchange inhibitor, CGP-37157 inhibited Ca²⁺ transients in ICC-MY. Effects were not due to depletion of ATP, as oligomycin did not affect Ca²⁺ transients. Patch-clamp experiments were performed to test the effects of the mitochondrial drugs on key pacemaker conductances, Ano1 and T-type Ca²⁺ (Ca_V3.2), in HEK293 cells. Antimycin blocked Ano1 and reduced Ca_V3.2 currents. CCCP blocked Ca_V3.2 current but did not affect Ano1 current. Ano1 and Cav3.2 currents were inhibited by CGP-37157. Inhibitory effects of mitochondrial drugs on slow waves and Ca²⁺ signalling in ICC can be explained by direct antagonism of key pacemaker conductances in ICC that generate and propagate slow waves. A direct obligatory role for mitochondria in pacemaker activity is therefore questionable.     

Clotrimazole-sensitive K+ currents regulate pacemaker activity in interstitial cells of Cajal

Interstitial cells of Cajal (ICC) are pacemaker cells for gut peristaltic motor activity. Compared with cardiac pacemaker cells, little is known about mechanisms that regulate ICC excitability. The objective of the present study was to investigate a potential role for clotrimazole (CTL)-sensitive K currents (I(CTL)) in the regulation of ICC excitability and pacemaker activity. ICC were studied in situ and in short-term culture by using the whole cell patch-clamp configuration. In situ, ICC exhibited spontaneous transient inward currents followed by transient outward currents. CTL blocked outward currents, thereby increasing the net inward currents, and depolarized ICC, thereby establishing CTL-sensitive channels as regulators of ICC pacemaker activity. In short-term culture, a I(CTL) was identified that showed increased conductance when depolarized from the resting membrane potential to 0 mV and subsequent inward rectification at further depolarized potentials. The I(CTL) markedly increased with increasing intracellular calcium and was insensitive to the ether-à-go-go-related K channel blocker E-4031 and the large-conductance calcium-activated K channel blocker iberiotoxin. I(CTL) contributed 3-9 nS to the whole cell conductance at 0 mV membrane potential under physiological conditions; it was fast activating (tau = 88 ms), showed little time-dependent inactivation, and exhibited a deactivation time constant of 38 ms. The nitric oxide donor sodium nitroprusside (SNP) increased I(CTL). Single-channel activity, activated by calcium and SNP, was inhibited by CTL, with a single-channel conductance of approximately 38 pS. In summary, ICC generate a I(CTL) on depolarization through an intermediate-conductance calcium-activated K channel that regulates pacemaker activity and ICC excitability.     

Development of c‐kit immunopositive interstitial cells of Cajal in the human stomach

Interstitial cells of Cajal (ICC) include several types of specialized cells within the musculature of the gastrointestinal tract (GIT). Some types of ICC act as pacemakers in the GIT musculature, whereas others are implicated in the modulation of enteric neurotransmission. Kit immunohistochemistry reliably identifies the location of these cells and provides information on changes in ICC distribution and density. Human stomach specimens were obtained from 7 embryos and 28 foetuses without gastrointestinal disorders. The specimens were 7–27 weeks of gestational age, and both sexes are represented in the sample. The specimens were exposed to anti‐c‐kit antibodies to investigate ICC differentiation. Enteric plexuses were immunohistochemically examined by using anti‐neuron specific enolase and the differentiation of smooth muscle cells (SMC) was studied with anti‐α smooth muscle actin and anti‐desmin antibodies. By week 7, c‐kit‐immunopositive precursors formed a layer in the outer stomach wall around myenteric plexus elements. Between 9 and 11 weeks some of these precursors differentiated into ICC. ICC at the myenteric plexus level differentiated first, followed by those within the muscle layer: between SMC, at the circular and longitudinal layers, and within connective tissue septa enveloping muscle bundles. In the fourth month, all subtypes of c‐kit‐immunoreactivity ICC which are necessary for the generation of slow waves and their transfer to SMC have been developed. These results may help elucidate the origin of ICC and the aetiology and pathogenesis of stomach motility disorders in neonates and young children that are associated with absence or decreased number of these cells.     

Roles of Interleukin-9 in the Growth and Cholecystokinin-Induced Intracellular Calcium Signaling of Cultured Interstitial Cells of Cajal

Interstitial cells of Cajal (ICC) are pacemaker cells in the gastrointestinal (GI) tract and loss of ICC is associated with many GI motility disorders. Previous studies have shown that ICC have the capacity to regenerate or restore, and several growth factors are critical to their growth, maintenance or regeneration. The present study aimed to investigate the roles of interleukin-9 (IL-9) in the growth, maintenance and pacemaker functions of cultured ICC. Here, we report that IL-9 promotes proliferation of ICC, and culturing ICC with IL-9 enhances cholecystokinin-8-induced Ca²⁺ transients, which is probably caused by facilitating maintenance of ICC functions under culture condition. We also show co-localizations of cholecystokinin-1 receptor and IL-9 receptor with c-kit by double-immunohistochemical labeling. In conclusion, IL-9 can promote ICC growth and help maintain ICC functions; IL-9 probably performs its functions via IL-9 receptors on ICC.     

Characterization of in vitro gutlike organ formed from mouse embryonic stem cells

Using an embryoid body (EB) culture system, we have made a functional organlike cluster: the "gut" from embryonic stem (ES) cells (ES gut). There are many types of ES clusters, because ES cells have a pluripotent ability to develop into a wide range of cell types. Before inducing specific differentiation by exogenously added factors, we characterized comprehensive physiological and morphological properties of ES guts. Each ES gut has a hemispherical (or cystic) structure and exhibits spontaneous contractions [mean frequency: 13.5 ± 8.8 cycles per min (cpm)]. A dense distribution of interstitial cells of Cajal (ICC) was identified by c-Kit immunoreactivity, and specific subcellular structures of ICC and smooth muscle cells were identified with electron microscopy. ICC frequently formed close contacts with the neighboring smooth muscle cells and occasionally formed gap junctions with other ICC. Widely propagating intracellular Ca²⁺ concentration oscillations were generated in the ES gut from the aggregates of c-Kit immunopositive cells. Plateau potentials, possibly pacemaker potentials in ICC, and electrical slow waves were recorded for the first time. These events were nifedipine insensitive, as in the mouse gut. Our present results indicate that the rhythmic pacemaker activity generated in ICC efficiently spreads to smooth muscle cells and drives spontaneous rhythmic contractions of the ES gut. The present characterization of physiological and morphological properties of ES gut paves the way for making appropriate models to investigate the origin of rhythmicity in the gut. intracellular calcium concentration oscillation; interstitial cells of Cajal; peristalsis     

Action potentials in gastrointestinal smooth muscle.

Recent investigation of the ultrastructure and electrophysiology of gastrointestinal smooth muscle layers has revealed a fascinating heterogeneity in cell type, cell structure, intercellular communication, and generated electrical activities. Networks of interstitial cells of Cajal (ICC) have been identified in many muscle layers and evidence is accumulating for a role of these networks in gut pacemaking activity. Synchronized motility in the organs of the gut result from interaction between ICC, neural-tissue, and smooth muscle cells. Regulation of cell to cell communication between the different cell types will be an important area for further research. Progress has been made in the elucidation of the ionic basis of the slow wave type action potentials and the spike-like action potentials. The mechanism underlying smooth muscle autorhythmicity seems different from that encountered in cardiac tissue, and evidence exists for metabolic regulation of the frequency of slow wave type action potentials.