Do gap junctions couple interstitial cells of Cajal pacing and neurotransmission to gastrointestinal smooth muscle?

Expression of connexin 26 and connexin 43 is reduced in Hirschsprung's disease

BACKGROUND

Despite having an optimal pull-through operation, some children with Hirschsprung's disease (HSCR) continue to experience persistent bowel symptoms. Coordinated colonic electrical activity depends on intercellular communication between the enteric nerves, interstitial cells of Cajal (ICCs), smooth muscle cells, and fibroblast-like (platelet-derived growth factor receptor-alpha-positive) cells. Gap junctions are low-resistance channels composed of connexin (Cx) proteins which couple cells electrically and chemically. We aimed to evaluate the expression patterns of Cx26, Cx36, and Cx43 in the colon of children with HSCR and in healthy control colon.

MATERIALS AND METHODS

Entire resected colonic specimens were collected from children undergoing pull-through surgery for HSCR (n = 10). Colonic controls were collected at colostomy closure in children with imperforate anus (n = 8). Distribution of Cx26, Cx36, and Cx43 was assessed using double-labeled immunofluorescence and confocal microscopy. Protein expression was quantified using Western blot analysis.

RESULTS

Sparse punctate Cx36 expression was seen in the myenteric plexus in nerve trunks and some platelet-derived growth factor receptor-alpha-positive cell and ICC fibers. Cx26 was similarly distributed, although it was not coexpressed in ICCs. Cx43 was only coexpressed with ICCs in the myenteric plexus. Expression of Cx26 and Cx43 was markedly reduced in the aganglionic colon in HSCR compared to controls, while Cx26 expression was also moderately reduced in the ganglionic bowel in HSCR.

CONCLUSIONS

Reduced expression of Cx26 and Cx43 is implicated in the pathophysiology of colonic dysmotility in the aganglionic bowel as well as, in the case of Cx26, the ganglionic bowel in HSCR.

Roles of connexins and pannexins in digestive homeostasis

Connexin proteins are abundantly present in the digestive system. They primarily form gap junctions, which control the intercellular exchange of critical homeostasis regulators. By doing so, gap junctions drive a plethora of gastrointestinal and hepatic functional features, including gastric and gut motility, gastric acid secretion, intestinal innate immune defense, xenobiotic biotransformation, glycogenolysis, bile secretion, ammonia detoxification and plasma protein synthesis. In the last decade, it has become clear that connexin hemichannels, which are the structural precursors of gap junctions, also provide a pathway for cellular communication, namely between the cytosol and the extracellular environment. Although merely pathological functions have been described, some physiological roles have been attributed to connexin hemichannels, in particular in the modulation of colonic motility. This equally holds true for cellular channels composed of pannexins, connexin-like proteins recently identified in the intestine and the liver, which have become acknowledged key players in inflammatory processes and that have been proposed to control colonic motility, secretion and blood flow.

Functional alterations in gut contractility after connexin36 ablation and evidence for gap junctions forming electrical synapses between nitrergic enteric neurons

Neurons in the enteric nervous system utilize numerous neurotransmitters to orchestrate rhythmic gut smooth muscle contractions. We examined whether electrical synapses formed by gap junctions containing connexin36 also contribute to communication between enteric neurons in mouse colon. Spontaneous contractility properties and responses to electrical field stimulation and cholinergic agonist were altered in gut from connexin36 knockout vs. wild-type mice. Immunofluorescence revealed punctate labelling of connexin36 that was localized at appositions between somata of enteric neurons immunopositive for the enzyme nitric oxide synthase. There is indication for a possible functional role of gap junctions between inhibitory nitrergic enteric neurons.

Long-term culture and cryopreservation of interstitial cells of Cajal

OBJECTIVE

Interstitial cells of Cajal (ICCs) in the gastrointestinal tract generate and propagate slow waves and mediate neuromuscular neurotransmission. Damage to ICCs has been described in several gastrointestinal motor disorders, and although many studies have examined ICCs in culture, they have been largely limited to freshly dissociated cells or short-term cultures. An efficient and reliable method to establish a source of ICCs is much needed. The aim of this study was to investigate methods for culturing, subculturing, cryopreservation, and recovery of ICCs.

METHODS

ICCs were derived from intestinal segments of domestic rabbits, and immunohistochemistry for c-Kit was used to identify ICCs in culture and after recovery. Recovered ICCs were also examined for motilin receptor expression.

RESULTS

Optimal conditions for ICC culture and cryopreservation were based on cell growth curves and MTT assay. On the basis of these findings, recovered cells were cultured for 7 days and then sorted via flow cytometry based on c-Kit immunoreactivity. The percent of c-Kit positive cells was 64.3%, and the number of ICCs sorted was 6.7 × 10(5). Reverse-transcription polymerase chain reaction and western blotting verified motilin receptor expression in c-Kit-positive ICCs.

CONCLUSIONS

This is the first study to describe the culture, passage, and recovery of ICCs and to show motilin receptor expression. Our results suggest that ICCs play an important role, at least in some species, in initiating the migrating myoelectric complex induced by motilin.

Acupuncture improves the repair and regeneration of interstitial cells of Cajal in rats after enteroenterostomy

AIM: To explore the mechanism by which acupuncture promotes intestinal motility.

METHODS: Thirty Sprague-Dawley rats were randomly divided into blank group, model group (receiving colocolic anastomosis) and acupuncture group. The acupuncture group underwent acupuncture at Zusanli, Sanyinjiao and Taichong daily for three continuous days. After acupuncture treatment, defecation was observed and intestinal propulsive rate was measured. Tissue samples of the colon which was 2 cm below the caecum were taken to observe the ultrastructure of interstitial cells of Cajal (ICC) and the Ache-ICC-SMC network.

RESULTS: In the acupuncture group, the time to first postoperative passage of feces was shortened and intestinal propulsive rate was improved compared with the model group [(2.00 ± 0.47) d vs (2.50 ± 0.53) d, (66.30 ± 4.21)% vs (46.33 ± 5.56)% , both P < 0.05]. Compared with the blank group, the damage of ICC ultrastructure in the model group was more significant while that in the acupuncture group was milder. In the model group, the ENS-ICC-SMC structure was disorganized, and the number of ICC and their fluorescence intensity were greatly decreased compared with the blank group [(18.67 ± 6.11) vs(32.33 ± 5.51), (35.00 ± 9.54) vs (58.67 ± 10.21), both P < 0.05]. In contrast, in the acupuncture group, the damage of the network structure was milder, and the number of ICC and their fluorescence intensity were increased compared with the model group [(30.33 ± 3.21) vs (18.67 ± 6.11), (56.67 ± 9.45) vs (35.00 ± 9.54), both P < 0.05]. Similar results were also obtained for the number of VAChT-positive nerve fibres [(18.67 ± 3.79) vs (20.67 ± 3.21), (20.33 ± 5.13) vs (34.67 ± 6.81), (23.00 ± 4.58) vs (18.67 ± 3.79), (36.00 ± 8.19) vs (20.33 ± 5.13), all P < 0.05].

CONCLUSION: Acupuncture can improve intestinal motility in rats after abdominal operation perhaps by improving the repair and regeneration of ICC.

Presence of cyclic nucleotide-gated channels in the rat urethra and their involvement in nerve-mediated nitrergic relaxation

We have addressed the distribution of cGMP-gated channels (CNG) in the rat urethra for the first time, as well as their putative role in mediating of the relaxation elicited by electrical field stimulation of nitrergic nerves. Functional studies have shown that specifically blocking CNG with L-cis-diltiazem leads to the rapid inhibition of urethral relaxation induced either by nitric oxide (NO) released by the nerves or by soluble guanylate cyclase activated with YC-1. By contrast, nerve-mediated noradrenergic contractions were only slowly and mildly reduced by L-cis-diltiazem. This effect was mimicked by lower concentrations of the D-diltiazem isomer, probably due to the nonspecific inhibition of voltage-dependent calcium channels. However, D-diltiazem did not affect relaxation responses. The expression of heteromeric retinal-like CNGA1 channels was demonstrated by conventional PCR on mRNA from the rat urethra. These channels were located in a subpopulation of intramuscular interstitial cells of Cajal (ICC) as well as in smooth muscle cells, although they were less abundant in the latter. CNG channels could not be visualized in any nervous structure within the urethral wall, in agreement with the emerging view that a subset of ICC serves as a target for NO. These channels could provide a suitable ionic mechanism to associate the changes in cytosolic calcium with the activation of the nitric NO-cGMP pathway and relaxation although the precise mechanisms involved remain to be elucidated.

Inherent rhythmicity and interstitial cells of Cajal in a frog vein

Interstitial cells of Cajal are responsible for rhythmic contractions of the musculature of the gastrointestinal tract and blood vessels.The existence of these cells and spontaneous rhythmicity were noticed in amphibian vein and the findings are reported in this paper.The postcaval vein was identified in the frog, Rana tigrina and was perfused with amphibian Ringer solution after isolation.Contractile activity was recorded through a tension transducer connected to a polygraph.The isolated postcaval vein showed spontaneous rhythmic activity. Addition of cold Ringer solution decreased, while warm Ringer increased, the rate of contraction. Adrenaline caused inhibition of rhythmic activity at a dosage that increased the rate of isolated sinus venosus.Sections of the postcaval vein,when stained supravitally with methylene blue, showed the presence of interstitial cells of Cajal. Photic stimulation of the vein in the presence of methylene blue led to a significant decrease in the rate of spontaneous beating of the vein.These findings indicate that the postcaval vein of frog is capable of inherent rhythmcity, which is dependent on the interstitial cells of Cajal but is independent of the sinus venosus.

Are interstitial cells of Cajal plurifunction cells in the gut?

The proposed functions of the interstitial cells of Cajal (ICC) are to 1) pace the slow waves and regulate their propagation, 2) mediate enteric neuronal signals to smooth muscle cells, and 3) act as mechanosensors. In addition, impairments of ICC have been implicated in diverse motility disorders. This review critically examines the available evidence for these roles and offers alternate explanations. This review suggests the following: 1) The ICC may not pace the slow waves or help in their propagation. Instead, they may help in maintaining the gradient of resting membrane potential (RMP) through the thickness of the circular muscle layer, which stabilizes the slow waves and enhances their propagation. The impairment of ICC destabilizes the slow waves, resulting in attenuation of their amplitude and impaired propagation. 2) The one-way communication between the enteric neuronal varicosities and the smooth muscle cells occurs by volume transmission, rather than by wired transmission via the ICC. 3) There are fundamental limitations for the ICC to act as mechanosensors. 4) The ICC impair in numerous motility disorders. However, a cause-and-effect relationship between ICC impairment and motility dysfunction is not established. The ICC impair readily and transform to other cell types in response to alterations in their microenvironment, which have limited effects on motility function. Concurrent investigations of the alterations in slow-wave characteristics, excitation-contraction and excitation-inhibition couplings in smooth muscle cells, neurotransmitter synthesis and release in enteric neurons, and the impairment of the ICC are required to understand the etiologies of clinical motility disorders.

Identification of a vaginal pacemaker: An immunohistochemical and morphometric study

Vaginal electric waves spread caudally in the vagina. We investigated the hypothesis that electric waves originate from a centre of interstitial cells of Cajal (ICCs) in the proximal vagina. Specimens (0.75 x 0.75 cm) were obtained from the vaginal walls of 23 cadavers (age 38.2 +/- 10.2 years). Sections were prepared for immunohistochemical investigations using the specific ICC marker, C-kit. Morphometric studies for image analysis using a Leica imaging system were performed. C-kit positive cells were detected in vaginal smooth muscle. Results from image analyser revealed that mean area percent of positive immunoreactivity for C-kit in the upper part of posterior vaginal wall was significantly higher (p < 0.0001) than of areas in other vaginal walls, and also significantly higher (p < 0.05) in circular than in longitudinal muscle layer. Studies have shown that the greatest collection of ICCs occurred in the upper part of the posterior vaginal wall. The vaginal electric waves are suggested to originate from this 'centre' and spread caudally.

Are gap junctions truly involved in inhibitory neuromuscular interaction in mouse proximal colon?

1. Gap junctions exist between circular muscle cells of the colon and between interstitial cells of Cajal (ICC) in the myenteric plexus of the gastrointestinal tract. They also probably couple intramuscular ICC with smooth muscle cells. Recent functional evidence for this was found in dye-coupling and myoelectrical experiments. 2. In the present study, we tested the hypothesis of gap junctions putatively being involved in neuromuscular interaction in mouse colon by using different classes of gap junction blockers. 3. Electrical field stimulation of the myenteric plexus elicited tetrodotoxin-sensitive and hexamethonium-independent fast and slow inhibitory junction potentials (fIJP and sIJP, respectively) in circular smooth muscle cells, as evaluated by intracellular recording techniques in impaled smooth muscle cells. Heptanol produced a time-dependent hyperpolarization of the membrane potential (MP) and abolished fIJP and sIJP. Octanol had no effect on the MP and abolished fIJP and sIJP. Carbenoxolone produced a time-dependent depolarization of the MP without any effect on fIJP or sIJP. The connexin 43 mimetic gap junction blocker GAP-27 had no effect on MP, fIJP or sIJP. 4. Based on the presently available gap junction blockers we found no evidence that gap junctions are involved in neuromuscular transmission in mouse colon, as suggested by morphological studies.

Interstitial cells of cajal in patients with constipation due to total colonic inertia

Colonic wall contains interstitial cells of Cajal. In view of studies demonstrating that Cajal cells generate electric waves which are presumably responsible for colonic motor activity, and that these waves are absent in total colonic inertia, we investigated the hypothesis that colonic Cajal cells might be disordered in patients with total colonic inertia. The study comprised 28 patients (age 41.6 +/- 8.2 SD years, 19 women, 9 men) with total colonic inertia in whom total colectomy was performed. Colonic specimens obtained from normal segments of the excised colon of 24 cancer patients acted as controls. Specimens were subjected to c-kit immunohistochemistry. Controls for antisera specificity consisted of tissue incubated with normal rabbit serum that had been substituted for the primary antiserum. C-kit-positive branched Cajal-like cells were detected in the musculature of the normal colonic segments. They were distinguishable from the C-kit-negative smooth muscle cells and the C-kit-positive but unbranched mast cells. No Cajal cells were detected in colon of total colonic inertia patients. The absence of Cajal cells in patients with total colonic inertia can be assumed to explain the absence of electric waves and motile activity previously reported in these patients. Further studies are needed to investigate the cause of Cajal-cell absence.

The identification of specialized pacemaking cells in the anal sphincters

BACKGROUND AND AIMS

Interstitial cells of Cajal (ICC) are claimed to generate the electrical activity in the colon and stomach. As the external (EAS) and internal (IAS) anal sphincters exhibit resting electrical activity, we hypothesized the presence of ICC in these sphincters. This hypothesis was investigated in the current study.

PATIENTS/METHODS

Specimens from the EAS and IAS were taken from normal areas of the anorectum which had been surgically excised by abdominoperineal operation for rectal cancer of 28 patients (16 men, 12 women, mean age 42.2+/-4.8 years). The specimens were subjected to c-kit immunohistochemistry. Controls for the specificity of the antisera consisted of tissue incubation with normal rabbit serum substituted for the primary antiserum.

RESULTS/FINDINGS

Fusiform, c-kit positive, ICC-like cells were detected in the anal sphincters; they had dendritic processes. They were clearly distinguishable from the non-branching, c-kit negative smooth and striated muscle cells of the anal sphincters. The specimens contained also c-kit positive mast cells, but they had a rounded body with no dendritic processes. Immunoreactivity was absent in negative controls in which the primary antibody was omitted.

INTERPRETATION/CONCLUSION

We have identified, for the first time, cells in EAS and IAS with morphological and immunological phenotypes similar to ICCs of the gut. These cells appear to be responsible for initiating the slow waves recorded from the anal sphincters and for controlling their activity. A deficiency or absence of these cells may affect the anal motile activity. Studies are needed to explore the role of these cells in anal motility disorders.

STW 5 (Iberogast) and its individual herbal components modulate intestinal electrophysiology of mice

STW 5 (Iberogast), a phytomedicine agent consisting of a fixed combination of nine individual plant extracts, is widely used in the treatment of dyspepsia and motility related disorders. Little if anything is known on the possible influence on electrophysiological properties of intestinal smooth muscle by which STW 5 causes its beneficial effects. The aim of the present study was to investigate whether herbal extracts influence electrophysiological parameters of large and small intestine. For this purpose intracellular recordings of smooth muscle cell (SMC) of the circular muscle layer of different parts of mouse intestine were performed using standard microelectrode techniques. The resting membrane potential (RMP), excitatory and inhibitory neurotransmission in proximal colon, the frequency and the amplitude of slow waves in small intestine were investigated. The RMP of SMC was -46.4+/-3.8 mV, n=11 in the colon and -59+/-1.3 mV, n=15 in small intestine. STW 5 significantly depolarized the RMP of colonic (16.6+/-2.2 mV, n=6, p<0.05) and jejunal (9.6+/-1.6 mV, n=7, p<0.05) SMC. This depolarizing effect can be mainly attributed to the constituents of chamomile flower, Angelica root and greater celandine herb. Following the electrical field stimulations (EFSs), junction potentials are influenced in a distinct manner. Excitatory junctions potentials (EJPs) of the colon were not significantly reduced (13.1+/-4.8 vs. 10.1+/-2.8 n.s., n=6) but fast (fIJP) and slow (sIJP) inhibitory junction potentials of the murine colon are reduced significantly by STW 5 (fIJP: 21.6+/-8.1 vs. 11.6+/-2.1 and sIJP: 12.1+/-3.3 vs. 6.1+/-1.3 n=6, p<0.05). The basal frequency of small intestinal slow waves was 39.5+/-1.4 min(-1) and the amplitude was 23.1+/-0.9 mV, n=15. STW 5 significantly reduced amplitude and frequency of the slow waves (11.7+/-0.8 mV; 33.5+/-3.4 min(-1), n=6, p<0.05). This effect on slow waves represents the summation of effects of the nine individual phytoextracts. Whereas Angelica root and chamomile flower completely blocked the slow wave activity, bitter candy tuft increased the frequency and amplitude, greater celandine herb reduced frequency and amplitude of the slow wave, peppermint leaf reduced frequency and left amplitude unchanged and liquorice root, caraway fruit and lemon balm leaf had no effects in basic electrophysiological properties of SMC. This study demonstrates that STW 5 causes changes in SMC RMP, excitatory and inhibitory neurotransmission and slow wave rhythmicity. These effects represent a summation effect of different constituents of this phytotherapeuticum and prove that STW 5 has characteristic effects on intestinal electrophysiology.

Electric waves recorded from the testicle: are they capsular or from the testicular tissue?

We demonstrated in a previous study that electric waves could be recorded from the testicle by applying the electrodes either directly to the tunica albuginea (TA) or transcutaneously. As the TA contains smooth muscle fibres which presumably transmit the electric waves, we investigated the hypothesis that the electric waves recorded from the testicle originated from the TA. During the repair of inguino-scrotal hernia in 24 men [age 36.6 +/- 8.6 years (mean +/- SD)], the tunica vaginalis was everted because of the presence of hydrocele. The electric activity of the TA was recorded by three surface electrodes and that of the testicle by three needle electrodes. The recorded potentials were amplified and displayed on an electromyographic apparatus. Triphasic slow waves (SWs) were recorded from the TA. They showed similar frequency, amplitude and conduction velocity from the three electrodes of the individual subject and were reproducible. They were followed or superimposed by bursts of action potentials (APs) which occurred randomly. No waves were recorded from the three needle electrodes inserted into the testicular tissue. The current study could demonstrate that the electric waves recorded from the electrodes applied to the testicle were derived from the TA and not from the testicular tissue. This finding apparently denotes that the TA has a resting tone and probably motile activity, the role of which in testicular function needs to be studied.

Identification of c-kit-positive cells in the human prostate: the interstitial cells of Cajal

The prostate exhibits electric activity in the form of slow waves (SWs) and action potentials (APs). As the interstitial cells of Cajal (ICCs) are considered the pacemaker cells which generate the electric waves, we investigated the hypothesis that the prostate contains ICC. Prostatic biopsies were obtained from 15 healthy volunteers (mean age 36 +/- 3.8 SD years). They were subjected to c-kit immunohistochemistry. Controls for the specificity of the antisera consisted of tissue incubated with normal rabbit serum substituted for the primary antiserum. C-kit-positive cells were identified as fusiform with dendritic processes. The cytoplasm was granular and the nucleus large and oval. Mast cells, also c-kit-positive, were round and lacked the dendritic processes. Immunoreactivity was absent in the negative controls. There were cells in the prostate with morphological and immunological phenotypes similar to ICCs of the gut. We predict an abnormal distribution of these cells in prostatic diseases. The study of the integrity of these cells may prove to be a useful investigative tool in the diagnosis of prostatic diseases and in the planning of an appropriate treatment.

Identification of interstitial cells of Cajal in human urinary bladder: concept of vesical pacemaker

OBJECTIVES

To determine whether, given the presence of interstitial cells of Cajal (ICCs) in organs that discharge slow waves, such as the gastrointestinal tract, such cells could also be present in the human urinary bladder (UB) and might exist in great numbers in the bladder dome, constituting the "primary pacemaker" from which slow waves spread to the body of the UB. This hypothesis was based on previous studies that had demonstrated the vesical electric waves starting in the dome and spreading caudad.

METHODS

Specimens (0.5 x 0.5 cm) from different vesical locations were obtained from the cystectomized UB of 18 patients (12 men, 6 women, mean age 42.6 +/- 3.8 years) with bladder cancer. Fixed sections were prepared and subjected to c-kit immunohistochemistry. Controls for the antiserum specificity consisted of incubation of the tissue with normal rabbit serum substituted for the primary antiserum.

RESULTS

Fusiform, c-kit positive, and ICC-like cells were detected in the vesical muscle layers; they had dendritic processes. They occurred separately or were connected through the dendritic processes to form a cellular network. An accumulation of ICCs surrounded by a connective tissue layer was detected in all the dome specimens. Mast cells occurred in the vesical mucosa and submucosa; they were c-kit positive but had a rounded body with no dendritic processes.

CONCLUSIONS

We identified cells in the UB with morphologic and immunologic phenotypes similar to the ICCs of the gut. An accumulation of these cells, detected in the vesical dome, seems to constitute the "primary" vesical pacemaker that initiates the slow waves that spread to the other vesical walls. We believe that a deficiency or absence of these cells may be involved in vesical motility disorders. Additional studies are needed to delineate the role of these cells in UB physiology and pathologic conditions.

Comparisons of neural and pacing activities in intestinal segments from W/W++ and W/W(V) mice

We studied pacing and neurotransmission in longitudinal (LM) and circular muscle (CM) in intestine of W/W++ and W/W(V) mice. Electrical field-stimulation (EFS) of nerves in LM segments was more inhibitory in W/W(V) mice than in W/W++ mice. No inhibitory input to CM segments of W/W(V) mice was found. The EFS, after nerve block, entrained segments of both W/W++ and mutant mice with 10 ms pulses, and entrained those of mutant mice more readily at 1 and 3 ms pulses. Pacing with external electrodes did not depend on interstitial cells of Cajal in the myenteric plexus (ICC-MP). 2-Aminoethoxydiphenyl borate (2-APB), putative antagonist at IP3 receptors, store-operated channels and the Sacro-endoplasmic reticulum Ca2+ ATPase pump, reduced frequency and amplitudes of pacing of LM segments from W/W(V) mice as it did in BALB/c mice. Thus, its actions may not require ICC-MP. SKF 96365, a putative inhibitor of store-operated channels, reduced frequencies and amplitudes of intestinal segments in W/W++ mice at 10 or 30 micromol L-1. This resulted from blocking L-Ca2+-channels. Thus, no evidence was found that store-operated channels play a role in pacing. In LM segments of W/W(V), SKF 96365 had no effects on frequency of contractions. We conclude, results from models of severely reduced systems may not be applicable to intact ICC networks.

Immunohistochemical identification of the pacemaker cajal cells in the normal human vagina

OBJECTIVES

It is claimed that the electric waves recorded from the gut and urinary system are generated from specialized cells called interstitial cells of Cajal (ICCs). As the vagina exhibits electric activity, we investigated the hypothesis that ICCs could be detected in its wall.

METHODS

Vaginal specimens were obtained from 28 female cadavers (mean age 34.8+/-10.8 SD years) and fixed sections were prepared for immunohistochemical investigations using the specific ICC marker c-kit. Controls for antisera specificity consisted of tissue incubated with normal rabbit serum substituted for the primary antiserum.

RESULTS

Branching, c-kit-positive ICC-like cells were found in the muscular layer of the vagina. They were clearly distinguishable from the smooth muscle cells which were c-kit negative and not branched and from the c-kit positive non-branched mast cells. Immunoreactivity was absent in the negative controls.

CONCLUSIONS

We have, for the first time, identified in the vagina ICCs that may be responsible for initiating the slow waves recorded from the vaginal smooth muscle cells.

Effects of the gap junction blocker glycyrrhetinic acid on gastrointestinal smooth muscle cells

In the tunica muscularis of the gastrointestinal (GI) tract, gap junctions form low-resistance pathways between pacemaker cells known as interstitial cells of Cajal (ICCs) and between ICC and smooth muscle cells. Coupling via these junctions facilitates electrical slow-wave propagation and responses of smooth muscle to enteric motor nerves. Glycyrrhetinic acid (GA) has been shown to uncouple gap junctions, but previous studies have shown apparent nonspecific effects of GA in a variety of tissues. We tested the effects of GA using isometric force measurements, intracellular microelectrode recordings, the patch-clamp technique, and the spread of Lucifer yellow within cultured ICC networks. In murine small intestinal muscles, beta-GA (10 muM) decreased phasic contractions and depolarized resting membrane potential. Preincubation of GA inhibited the spread of Lucifer yellow, increased input resistance, and decreased cell capacitance in ICC networks, suggesting that GA uncoupled ICCs. In patch-clamp experiments of isolated jejunal myocytes, GA significantly decreased L-type Ca(2+) current in a dose-dependent manner without affecting the voltage dependence of this current. The IC(50) for Ca(2+) currents was 1.9 muM, which is lower than the concentrations used to block gap junctions. GA also significantly increased large-conductance Ca(2+)-activated K(+) currents but decreased net delayed rectifier K(+) currents, including 4-aminopyridine and tetraethylammonium-resistant currents. In conclusion, the reduction of phasic contractile activity of GI muscles by GA is likely a consequence of its inhibitory effects on gap junctions and voltage-dependent Ca(2+) currents. Membrane depolarization may be a consequence of uncoupling effects of GA on gap junctions between ICCs and smooth muscles and inhibition of K(+) conductances in smooth muscle cells.

Proteins of interstitial cells of Cajal and intestinal smooth muscle, colocalized with caveolin-1

The murine jejunum and lower esophageal sphincter (LES) were examined to determine the locations of various signaling molecules and their colocalization with caveolin-1 and one another. Caveolin-1 was present in punctate sites of the plasma membranes (PM) of all smooth muscles and diffusely in all classes of interstitial cells of Cajal (ICC; identified by c-kit immunoreactivity), ICC-myenteric plexus (MP), ICC-deep muscular plexus (DMP), ICC-serosa (ICC-S), and ICC-intramuscularis (IM). In general, all ICC also contained the L-type Ca(2+) (L-Ca(2+)) channel, the PM Ca(2+) pump, and the Na(+)/Ca(2+) exchanger-1 localized with caveolin-1. ICC in various sites also contained Ca(2+)-sequestering molecules such as calreticulin and calsequestrin. Calreticulin was present also in smooth muscle, frequently in the cytosol, whereas calsequestrin was present in skeletal muscle of the esophagus. Gap junction proteins connexin-43 and -40 were present in circular muscle of jejunum but not in longitudinal muscle or in LES. In some cases, these proteins were associated with ICC-DMP. The large-conductance Ca(2+)-activated K(+) channel was present in smooth muscle and skeletal muscle of esophagus and some ICC but was not colocalized with caveolin-1. These findings suggest that all ICC have several Ca(2+)-handling and -sequestering molecules, although the functions of only the L-Ca(2+) channel are currently known. They also suggest that gap junction proteins are located at sites where ultrastructural gap junctions are know to exist in circular muscle of intestine but not in other smooth muscles. These findings also point to the need to evaluate the function of Ca(2+) sequestration in ICC.

Intercellular coupling of interstitial cells of cajal in the digestive tract

Interstitial cells of Cajal (ICC) are essential for the normal function of the digestive tract, both as pacemakers and as intermediates between nerves and smooth muscle cells. To perform their functions ICC must be electrically coupled both among themselves and to the muscle layers. This review focuses on the role gap junctions play in coupling ICC to ICC, providing a summary of the published literature as well as a critical appraisal of the data. Most of the experimental evidence for gap junction coupling of ICC networks is indirect, and consists of the ultrastructural observation of gap junctions. Dye coupling studies provide consistent support for the role of gap junctions among ICC of certain types. Physiological evidence in support of this role is scarce. The nature of ICC to smooth muscle coupling is even less certain.

Response of the internal reproductive organs to clitoral stimulation: The clitorouterine reflex

We investigated hypothesis that uterine erection, elevation and enlargement during sexual response are reflex and result from penis buffeting the glans clitoris (GC). In 23 healthy women, two recording electrodes were applied to the uterine mucosa and one to cervix uteri (CU). GC was stimulated electrically and mechanically by pencil electrode. The uterine and CU pressures were measured. Tests were repeated after anesthetization of the uterus or GC. Uterine electrodes recorded slow waves, followed by random bursts of action potentials (APs). No waves registered from CU. Electrical or mechanical GC stimulation eliminated uterine electric waves, but anesthetized GC did not, nor did GC stimulation while the uterus anesthetized. Uterine pressure declined on electrical or mechanical stimulation. Results suggest presence of reproducible reflex relationship between GC and the uterus, we call 'clitorouterine reflex'. GC buffeting seems to evoke reflex and initiate uterine responses. Reflex may prove of diagnostic significance in sexual disorders.

Electroesophagogram in gastroesophageal reflux disease with a new theory on the pathogenesis of its electric changes

Background

In view of the disturbed esophageal peristaltic activity and abnormal esophageal motility in gastroesophageal reflux disease, (GERD), we investigated the hypothesis that these changes result from a disordered myoelectric activity of the esophagus.

Methods

The electric activity of the esophagus (electroesophagogram, EEG) was studied in 27 patients with GERD (16 men, 11 women, mean age 42.6 ± 5.2 years) and 10 healthy volunteers as controls (6 men, 4 women, mean age 41.4 ± 4.9 years). According to the Feussner scoring system, 7 patients had a mild (score 1), 10 a moderate (score 2) and 10 a severe (score 3) stage of the disease. One electrode was applied to the upper third and a second to the lower third of the esophagus, and the electric activity was recorded. The test was repeated after the upper electrode had been moved to the mid-esophagus.

Results

The EEG of the healthy volunteers showed slow waves and exhibited the same frequency, amplitude and conduction velocity from the 2 electrodes of the individual subject, regardless of their location in the upper, middle or lower esophagus. Action potentials occurred randomly. In GERD patients, score 1 exhibited electric waves' variables similar to those of the healthy volunteers. In score 2, the waves recorded irregular rhythm and lower variables than the controls. Score 3 showed a "silent" EEG without waves.

Conclusion

The electric activity in GERD exhibited 3 different patterns depending on the stages of GERD. Score 1 exhibited a normal EEG which apparently denotes normal esophageal motility. Score 2 recorded irregular electric waves variables which are presumably indicative of decreased esophageal motility and reflux clearance. In score 3, a "silent" EEG was recorded with probably no acid clearance. It is postulated that the interstitial cells of Cajal which are the electric activity generators, are involved in the inflammatory process of GERD. Destruction of these cells appears to occur in grades that are in accordance with GERD scores. The EEG seems to have the potential to act as an investigative tool in the diagnosis of GERD stages.

Electromotor Activity of the Cecum and Ascending Colon: The Concept of ‘Individual Pacemakers’

BACKGROUND/AIMS

The cecum is described as differing anatomically from the ascending colon (AC); yet their similarity or difference in terms of motile activity has not been studied sufficiently. The cecum is separated from the AC by the cecocolonic junction (CCJ) which contains a cecocolonic sphincter. We assumed that the motile activity of the AC is different from that of the cecum and hypothesized that both the AC and the cecum might have different pacemakers which initiate the motile activity. This hypothesis was investigated in the current study.

METHODS

The study was performed in 10 subjects (mean age 41.6 +/- 12.8 SD years; 7 women) during the repair of huge abdominal incisional hernias. The electric activity was recorded from 2 monopolar electrodes applied each to the cecum, CCJ and AC. The CCJ was then anesthetized by xylocaine and the electric waves of the cecum, CCJ and AC were registered after 10 and 90 min. The test was repeated using normal saline instead of xylocaine.

RESULTS

Electric waves were recorded from the cecum, CCJ and AC in the form of monophasic pacesetter (PPs) and action potentials (APs). The PPs occurred regularly and the APs randomly. The frequency, amplitude and conduction velocity of the waves recorded from the CCJ and AC had higher readings than those from the cecum (p < 0.05). The CCJ and AC showed similar frequency and conduction velocity (p > 0.05). Ten minutes after CCJ anesthetization, electric waves were recorded from the cecum but not from the CCJ or AC; however, electric activity returned after 90 min. Saline injection did not affect the electric activity of the cecum, CCJ and AC.

CONCLUSION

The electric wave parameters of the cecum differed from those of the CCJ and AC, suggesting that the motile activity of the CCJ and AC is not a continuation of the motile activity of the cecum and that it might be evoked by 2 different pacemakers. The similarity in frequency and conduction velocity of electric waves of the CCJ and AC, however, most likely denotes that the AC waves are a continuation of those of the CCJ, and that both are evoked by the same pacemaker probably located in the CCJ. The higher amplitude of cecal waves might be due to the thicker cecal musculature compared to that of the AC.

Vesical pacing in patients with overactive bladder: technique and results

OBJECTIVES

A recent study has demonstrated that the electric activity of the overactive bladder (OAB) is 'dysrhythmic'. The cause was attributed to a disordered vesical pacemaker which discharges these waves. In a subsequent study, the dysrhythmic waves have been 'normalized' by vesical pacing and the optimal parameters which are required to achieve normalization have been defined. We investigated the hypothesis that vesical pacing of the OAB might improve not only the vesical electric activity but also the symptoms.

METHODS

Vesical pacing was used in 9 patients (age 39.2 +/- 10.3; 5 women, 4 men) with OAB. Under anesthesia, the pacemaker was implanted in an inguinal subcutaneous pocket and connected to 2 pacing electrodes implanted into the vesical vault. The normalization of the waves was tested by 2 recording electrodes which were temporarily applied to the vesical wall and removed post-testing. The pacemaker was then programmed for home pacing to be activated at given times.

RESULTS

Vesical pacing effected normalization of the dysrhythmic electric waves with disappearance of the OAB symptoms in 7 patients and failed in 2. Vesical pacing was abandoned in 3/7 patients after a few months following the spontaneous disappearance of the symptoms.

CONCLUSIONS

Vesical pacing has normalized the dysrhythmic electric activity and suppressed the symptoms of the OAB in 77.7% of patients. The pacemaker was removed in 5 patients: 2 failures and 3 after spontaneous waves normalization. No complications were encountered. Vesical pacing is suggested as a treatment for OAB when commonly used therapeutic modalities have failed.

Function of interstitial cells of Cajal in the rabbit portal vein

Interstitial cells of Cajal (ICCs) were identified in the intact fixed media of the rabbit portal vein (RPV) using c-kit staining. The following experiments were performed using single cell preparations of the enzyme-dispersed vessel. Surviving contacts between the processes of single ICCs and the bodies of smooth muscle cells (SMCs) were observed in electron micrographs and by confocal microscopy. Spontaneous rhythmical [Ca2+]i oscillations were observed in ICCs after loading with the calcium indicator fluo-3 and were associated with depolarizations of the ICCs recorded by tight-seal patch pipette. To investigate signal transmission from ICCs to SMCs in dispersed cell pairs, or within small surviving fragments of the ICC network, an ICC was stimulated under voltage-clamp, while changes in [Ca2+]i in the stimulated cell as well as in a closely adjacent SMC or ICCs were monitored using fast x-y confocal imaging of fluo-3 fluorescence. After stimulation of single voltage-clamped ICC by a depolarizing step similar in duration to depolarizations associated with spontaneous [Ca2+]i oscillations, a depolarization and transient elevation of [Ca2+]i was observed in a closely adjacent SMCs after a delay of up to 4 seconds. In contrast, signal transmission from ICC to ICC was much faster, the delay being less than 200 ms. These results suggest that the an ICC may, in addition to generating an electrical signal (such as a slow wave) and thereby acting as a pacemaker for vascular SMCs of RPV, also release some unknown diffusible substance, which depolarizes the SMCs.

Gastro-electric dysrhythm and lack of gastric interstitial cells of cajal

AIM: The pathophysiology underlying gastrointestinal complications of long-standing diabetes is poorly understood. Recent evidence suggests an important role of intestitial cells of cajal in controlling gastrointestinal motility. The aim of this study was to clarify the changes of ultrastructural characteristics of interstitial cells of cajal in stomach of diabetic gastro-electric dysrhythmic rats.

METHODS: Rats were randomly divided into diabetic group and control group, the model of diabetic rats was established by peritoneally injection of streptozotocin. Electrogastrograms were recorded and intestitial cells of cajal in antrum were observed by electrictelescopy after diabetic model rat was established for 3 mo.

RESULTS: In the rats of diabetic group, the gastro-electric dysrhythmia was increased compared with control group, the abnormal rhythm index and the cofficient of variation of slow wave frequency were significantly higher than those of normal rats. The number of the gap junctions of interstitial cells of cajal in antrum of diabetic rats was significantly decreased, and the remaining structures were damaged. The organelles were also damaged, and vacuoles were formed.

CONCLUSION: It is possible that changes in ultrastructural characteristics of interstitial cells of cajal in stomach are one of the mechanisms underlying gastro-electric dysrhythm in diabetic rats.

Communication between interstitial cells of Cajal and gastrointestinal muscle

Interstitial cells of Cajal (ICC) pace gastrointestinal muscle by initiating slow waves in both muscle layers and appear to be preferred sites for reception of neurotransmitters. ICC of the myenteric plexus (ICC-MP) pace stomach and small intestine, while intramuscular ICC (ICC-IM) receive nerve messages. Recently, ICC-IM have been found to provide regenerative responses to and amplification of pacing messages from ICC-MP, at least in some systems. This review will examine the assumption that gap junctions provide low-resistance contacts for pacing. Structural and functional evidence will be evaluated. Structural, theoretical and experimental difficulties with the gap junctions hypothesis for pacing will be considered. So far little direct evidence about the role of gap junctions in neurotransmission exists, although a structural basis exists. Alternate possibilities for transmission of ICC pacing and neural messages will be examined and suggestions for future research made.

The electrovesicogram in the overactive bladder: role in determining pathogenesis and diagnostic significance

We investigated the hypothesis that the abnormal contractility of the smooth musculature of the overactive bladder (OAB) may be due to derangement of its electrical activity. Percutaneous electrovesicography was performed in 22 patients (mean age 46.3 years, 12 men, ten women) with OAB and 14 healthy volunteers (mean age 45.6 years, eight men, six women). Recording was performed with the bladder full and empty. Three electrodes were applied suprapubically and one reference electrode was applied to a lower limb. Reproducible regular triphasic slow waves (SWs) were recorded in the volunteers. The pattern of the full and empty bladder were similar except for the higher amplitude of the waves in the former (P < 0.05). The OAB patients showed a "dysrhythmic" pattern with irregular frequency, amplitude and conduction velocity in both the empty and full bladders. We obtained tachyrhythmic, bradyrhythmic and arrhythmic areas in the same recording. The OAB exhibited a "dysrhythmic" electrical pattern with areas of different electrical activity in the same recording. The tachyrhythmic, bradyrhythmic and arrhythmic areas are suggested to explain the abnormal vesical contractions and clinical manifestations of OAB. Further studies are required to investigate the cause of the dysrhythmic pattern and the electrovesicogram is suggested as an investigative tool in OAB diagnosis.

A new model of pacing in the mouse intestine

A simple model of pacing in mouse intestine to longitudinal (LM) as well as circular muscle (CM) has been developed. Undissected segments of LM or CM from mouse ileum or jejunum were prepared to record contractions, nerve functions were inhibited, and regular spontaneous contractions were recorded. These had the properties expected of interstitial cells of Cajal (ICC) paced contractions: ileum slower than jejunum, inhibited but not abolished by nicardipine, reduced in frequency by cyclopiazonic acid, abolished by Ca(2+)-free media, and high temperature dependence (Q10 approximately 2.6-3.2). Nicardipine significantly reduced the pacing frequency in LM and CM. Intestinal segments from W/W(V) mice had few irregular contractions in CM but had regular contractions in LM. Other differences were found between LM and CM that suggest that the control of pacing of LM differed from pacing of CM. Moreover, both LM and CM segments in wild-type and W/W(V) and after cyclopiazonic acid responded to electrical pacing (50 V/cm, 50 or 100 ms) at 1 pulse per second. Temperature <26 degrees C inhibited electrically paced contractions in CM. These findings suggest that the current models of ICC pacing need to be modified to apply to intact segments of mouse intestine.

Coupling among interstitial cells of Cajal in the human ileum

Current knowledge on the morphology and physiology of interstitial cells of Cajal (ICC) is mostly based on animal studies, and information about the function of these cells in humans is scarce. There is ultrastructural evidence that ICC in the myenteric region (ICC-MP) of the small intestine of several species are connected by gap junctions, but these were not observed in the human small intestine. The aim of the present study was to determine whether functional coupling also exists among ICC-MP in the human ileum. We visualized ICC-MP in live tissues using Nomarski optics, and verified their identity by staining for c-Kit. ICC were injected intracellularly with the fluorescent dye Lucifer yellow, which crosses gap junctions. In most cases the labelled cells had oval somata with two primary processes. At normal pH (7.3-7.4) only 20.2% (21/104) of the injected ICC were coupled to other ICC. However, at pH 7.8-7.9 coupling incidence increased to 74.5% (35/47, P < 0.0001). The injected cells were coupled to one to 35 other ICC. Octanol blocked coupling in all cases. Apparently, gap junctions interconnect ICC in the human small intestine. Coupling was enhanced by a small increase in pH, suggesting that it may be under physiological control.

Electric activity of the colon in irritable bowel syndrome: the 'tachyarrhythmic' electric pattern

BACKGROUND AND AIM

The etiology of irritable bowel syndrome is unknown. It presents with crampy abdominal pain associated with alternating constipation and diarrhea but with no anatomic abnormality on diagnostic testing. Because the condition is related to motility disturbance, the hypothesis that a disorder of the colonic electromyographic activity is responsible for the colonic motile disorders in irritable bowel syndrome, was investigated.

METHODS

The electromyographic activity of the sigmoid colon was recorded transcutaneously in 18 patients with irritable bowel syndrome (49.6 +/- 10.2 years, 12 women) and 14 healthy volunteers (47.2 +/- 9.9 years; eight women) by applying three electrodes to the abdominal skin below the umbilicus. The sigmoid colon pressure was measured by means of a saline-perfused tube connected to a pneumohydraulic capillary infusion system.

RESULTS

Slow waves with a regular rhythm were recorded in the healthy volunteers exhibiting the same frequency, amplitude and conduction velocity from all three electrodes. Action potentials (AP) were not registered. The basal sigmoid colon pressure was interrupted by bouts of elevation. In irritable bowel syndrome, the electromyographic rhythm was irregular and the slow wave variables were higher than those of the normal volunteers and were not the same from the three electrodes; occasional AP were also recorded. The sigmoid colon basal pressure was significantly higher, and was interrupted by pressure bouts significantly higher, than those of the volunteers.

CONCLUSIONS

Irritable bowel syndrome exhibited a 'tachyarrhythmic' pattern of electromyographic activity with higher slow wave variables than normal and occasional AP. The resulting elevated basal colonic pressure and tone may explain some of the irritable bowel syndrome symptoms. Because diagnostic testing of the irritable bowel syndrome shows no anatomic abnormalities, it is suggested that the cause of irritable bowel syndrome is related to an abnormal focus in one or more of the colonic pacemakers emitting these abnormal waves. However, further studies are required to verify these findings.

Plasma membrane channels formed by connexins: their regulation and functions

Members of the connexin gene family are integral membrane proteins that form hexamers called connexons. Most cells express two or more connexins. Open connexons found at the nonjunctional plasma membrane connect the cell interior with the extracellular milieu. They have been implicated in physiological functions including paracrine intercellular signaling and in induction of cell death under pathological conditions. Gap junction channels are formed by docking of two connexons and are found at cell-cell appositions. Gap junction channels are responsible for direct intercellular transfer of ions and small molecules including propagation of inositol trisphosphate-dependent calcium waves. They are involved in coordinating the electrical and metabolic responses of heterogeneous cells. New approaches have expanded our knowledge of channel structure and connexin biochemistry (e.g., protein trafficking/assembly, phosphorylation, and interactions with other connexins or other proteins). The physiological role of gap junctions in several tissues has been elucidated by the discovery of mutant connexins associated with genetic diseases and by the generation of mice with targeted ablation of specific connexin genes. The observed phenotypes range from specific tissue dysfunction to embryonic lethality.

Does ICC pacing require functional gap junctions between ICC and smooth muscle in mouse intestine?

We tested the hypothesis that interstitial cells of Cajal (ICC) pace longitudinal and circular muscle of mouse intestine through gap junctions. Carbenoxolone (10(-6), 10(-5), 10(-4) mol L(-1)), an inhibitor of gap junction conductance, was applied to segments of longitudinal or circular muscle with contractions driven by ICC after inhibition of nerve function by tetrodotoxin (10(-6) mol L(-1)) and L-NOARG (10(-4) mol L(-1)). Carbenoxolone concentration- and time-dependently inhibited the amplitude of contraction (0.2-1.5 g in controls) of segments of longitudinal muscle, but had no effect on the frequency of contractions (from 36-54 min). It also inhibited the amplitude of contractions of circular muscle segments and reduced the frequency slightly at 10(-4) mol L(-)1. Carbenoxolone inhibited tonic contractions of longitudinal but not circular segments to 60 mmol L(-1) KCl, suggesting that it directly inhibited contractions of longitudinal muscle. The responses to pacing by electrical field stimulation (40 V cm(-1), 50-100 ms, 1 Hz) after block of nerve function were reduced insignificantly in amplitude, and not in frequency in both longitudinal and circular segments. We conclude that it is likely that only gap junctions within circular muscle are involved in pacing of muscle by ICC. Carbenoxolone also has effects on muscle contractility in longitudinal muscle.

Roles of guanylate cyclase in responses to myogenic and neural nitric oxide in canine lower esophageal sphincter

Whether cGMP and cytosolic guanylate cyclase (cGC) mediate responses of canine lower esophageal sphincter (LES) to nitric oxide (NO) released from nerves, produced in muscle, or added exogenously was evaluated in vitro. 1-H-(1,2,4)oxadiazole(4,3-alpha)quinoxalin-1-1 (ODQ), inhibitor of cGC, reduced relaxations to nerve stimulation and sodium nitroprusside but not to nitric-oxide synthase activity-dependent outward K(+)-currents in isolated muscle cells. ODQ also failed to increase tone after nerve blockade. Nonspecific K(+) channel blocker, TEA ion at 20 mM was previously shown to increase tone, occlude NO-mediated modulation of tone, and inhibit NO-dependent outward currents but not neural relaxation in LES cells. In this study, TEA abolished neural relaxation and nearly abolished relaxation to sodium nitroprusside when present with ODQ. We conclude that mechanisms coupling NO in canine LES to responses vary with the source of NO. ODQ-dependent mechanisms, presumably involving cGC, mediate actions of NO from nerves, but NO from muscle utilizes TEA-sensitive but not ODQ-dependent mechanisms to modulate tone and outward currents. Exogenous NO utilizes both TEA- and ODQ-dependent mechanisms.

The interstitial cells of Cajal and a gastroenteric pacemaker system

In spite of a claim by Kobayashi (1990) that they do not correspond to the cells originally depicted by CAJAL, a particular category of fibroblast-like cells have been identified in the gut by electron microscopy (Faussone-Pellegrini, 1977; Thuneberg, 1980) and by immunohistochemistry for Kit protein (Maeda et al., 1992) under the term of the "interstitial cells of Cajal (ICC)". Generating electrical slow waves, the ICC are intercalated between the intramural neurons and the effector smooth muscular cells, to form a gastroenteric pacemaker system. ICC at the level of the myenteric plexus (IC-MY) are multipolar cells forming a reticular network. The network of IC-MY which is believed to be the origin of electrical slow waves is morphologically independent from but associated with the myenteric plexus. On the other hand, intramuscular ICC (IC-IM) usually have spindle-shaped contours arranged in parallel with the bulk smooth muscle cells. Associated with nerve bundles and blood vessels, the IC-IM possess receptors for neurotransmitters and such circulating hormones as cholecystokinin, suggesting their roles in neuromuscular and hormone-muscular transmissions. In addition, gap junctions connect the IC-MY and IC-IM, thereby realizing the electrically synchronized integrity of ICC as a pacemaker system in the gut. The smooth muscle cells are also coupled with ICC via gap junctions, and the functional unit thus formed enables rhythmically synchronized contractions and relaxations. It has recently been found that a lack of Kit-expressing cells may induce hyper-contractility of the tunica muscularis in vitro, whereas a decrease in Kit expression within the muscle wall causes dysmotility-like symptoms in vivo. The pacemaker system in the gut thus seems to play a critical role in the maintenance of both moderate and normal motility of the digestive tract. A loss of Kit positive cells has been detected in several diseases with an impaired motor activity, including diabetic gastroenteropathy. Pathogenesis of these diseases is thought to be accounted for by impaired slow waves and neuromuscular transmissions; a pacemaker disorder may possibly induce a dysmotility-like symptom called 'gastroenteric arrhythmia'. A knowledge of the structure and function of the ICC and the pacemaker system provides a basis for clarifying the normal mechanism and the pathophysiology of motility in the digestive tract.