Interstitial cells of Cajal mediate enteric inhibitory neurotransmission in the lower esophageal and pyloric sphincters

Survival dependency of intramuscular ICC on vagal afferent nerves in the cat esophagus

Interstitial cells of Cajal (ICC) have been proposed as stretch receptors for vagal afferent nerves in the stomach based on immunohistochemical studies. The aim of the present study was to use electron microscopy and the anterograde degeneration technique to investigate ultrastructural features and survival dependency of ICC associated with vagal afferent innervation of the cat esophagus. This is the first report on the ultrastructural characteristics of ICC in the cat esophagus. Intramuscular ICC (ICC-IM) were identified throughout the musculature, whereas ICC in the myenteric plexus were rare. ICC-IM were particularly numerous in septa aligned with smooth muscle bundles. They were in synapse-like contact with nerve varicosities and in gap junction contact with smooth muscle cells. Smooth muscle cells also made contact with ICC through peg and socket junctions. Precision damage through small-volume injection of saline in the center of the nodose ganglion from the lateral side, known to selectively affect sensory nerves, was followed within 24 h by degeneration of a subset of nerve varicosities associated with ICC-IM, as well as degeneration of the associated ICC-IM. Smooth muscle cells were not affected. Nerves of Auerbachs plexus and associated ICC were not affected. In summary, ICC-IM aligning the esophageal muscle bundles form specialized synapse-like contacts with vagal afferent nerves as well as gap junction and peg-and-socket contacts with smooth muscle cells. This is consistent with a role of ICC-IM as stretch receptors associated with vagal afferent nerves; the ICC-vagal nerve interaction appears essential for the survival of the ICC.

Regulation of basal tone, relaxation and contraction of the lower oesophageal sphincter. Relevance to drug discovery for oesophageal disorders

The lower oesophageal sphincter (LOS) is a specialized region of the oesophageal circular smooth muscle that allows the passage of a swallowed bolus to the stomach and prevents the reflux of gastric contents into the oesophagus. The anatomical arrangement of the LOS includes semicircular clasp fibres adjacent to the lesser gastric curvature and sling fibres following the greater gastric curvature. Such anatomical arrangement together with an asymmetric intrinsic innervation and distinct proportion of neurotransmitters in both regions produces an asymmetric pressure profile. The LOS tone is myogenic in origin and depends on smooth muscle properties that lead to opening of L-type Ca(2+) channels; however it can be modulated by enteric motor neurons, the parasympathetic and sympathetic extrinsic nervous system and several neurohumoral substances. Nitric oxide synthesized by neuronal NOS is the main inhibitory neurotransmitter involved in LOS relaxation. Different putative neurotransmitters have been proposed to play a role together with NO. So far, only ATP or related purines have shown to be co-transmitters with NO. Acetylcholine and tachykinins are involved in the LOS contraction acting through acetylcholine M(3) and tachykinin NK(2) receptors. Nitric oxide can also be involved in the regulation of LOS contraction. The understanding of the mechanisms that originate and modulate LOS tone, relaxation and contraction and the characterization of neurotransmitters and receptors involved in LOS function are important to develop new pharmacological tools to treat primary oesophageal motor disorders and gastro-oesophageal reflux disease.

Interstitial cells of Cajal in health and disease. Part I: normal ICC structure and function with associated motility disorders

Ramon y Cajal (1852-1934) is considered to be one of the founders of the field of neuroscience. In 1911, he described interstitial neurons in the gut, noting that they were primitive accessory components that perhaps modify smooth muscle contraction, themselves subject to regulation from principle neurons. The accuracy of his description of their appearance and activities has led to these cells now being called the interstitial cells of Cajal (ICC). Thuneberg and Faussone-Pellegrini were instrumental in bringing these cells to the attention of gastroenterologists and pathologists in the early 1980s. Subsequently, the development of antibodies to c-kit has allowed routine identification of the ICC in pathology specimens. c-Kit is a transmembrane protein kinase which has as ligand stem cell factor and is involved in cell development in a variety of cell lineages. In the gut musculature, ICC and mast cells are the only cells that have prominent c-kit expression. The ICC are now known to play an important role in gut motility and absent or disordered ICC networks have been identified in a variety of motility disorders.

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

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

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.

5-HT receptors on interstitial cells of Cajal, smooth muscle and enteric nerves

The majority of the body's serotonin (5-HT) is produced by the gastrointestinal tract. 5-HT has several functions in the gastrointestinal tract. 5-HT is a paracrine signalling molecule released from enterochromaffin cells, a survival and proliferating factor and a neurotransmitter. The actions of 5-HT are transduced by a large family of 5-HT receptors, several of which are expressed on different gastrointestinal cell types including enteric nerves, smooth muscle and interstitial cells of Cajal (ICC). This review will summarize recent advances in understanding the role of 5-HT in regulating function of ICC, and the expression and function of 5-HT receptors on muscle and enteric nerves in human tissue. Rodent ICC express several 5-HT receptors including 5-HT(2B) receptors which regulate ICC survival and proliferation. Human smooth muscle and enteric neurons also express several 5-HT receptor subtypes. Expression and function of these receptors is significantly different from small laboratory animals. 5-HT(7) receptor activation causes relaxation of muscle, whereas 5-HT(2B) receptors increase muscle activity. The 5-HT(4) receptor appears to mediate both inhibition and activation of smooth muscle involving myogenic as well as neural actions. Despite the abundant expression of 5-HT(3) receptors in the human enteric nervous system no functional correlate has been as yet demonstrated.

Symptomatology, pathophysiology, diagnostic work-up, and treatment of Hirschsprung disease in infancy and childhood

In the majority of infants and children with constipation, no obvious cause can be identified. A rare cause of constipation is Hirschsprung disease (HD). HD is characterized by the absence of ganglion cells from the anorectum for a variable length up to the duodenum. The extent of the aganglionic segment varies, but in most patients the lesion does not extend beyond the rectum and sigmoid colon. This review focuses on the passage of meconium, the recognition of HD, and new insights in its pathophysiology and genetics. The authors also provide a summary of the diagnostic evaluation and treatment of HD in infancy and childhood.

Interstitial cells of Cajal and neuromuscular transmission in the rat lower oesophageal sphincter

The distribution of interstitial cells of Cajal (ICC) and neurotransmission were investigated in lower oesophageal sphincter (LES) circular muscle strips from Sprague-Dawley (SD) rats, Ws/Ws mutant rats and their wild-type (+/+) siblings. Intramuscular c-Kit-positive cells, confirmed to be ICC-IM by electron microscopy, were observed throughout both muscle layers from SD and +/+ rats. In contrast, c-Kit-positive, ultrastructurally typical ICC-IM were absent in Ws/Ws. LES strips from Ws/Ws rats showed increased spontaneous contractile activity. Strips from SD and +/+ rats, responded to electrical neuronal stimulation with a relaxation that was in part L-NNA and in part apamin sensitive, followed by a contraction which was decreased by atropine. In Ws/Ws rats, similar to +/+ rats, neurally mediated relaxation was L-NNA and apamin sensitive and the contraction was decreased by atropine. We conclude that in the rat LES, relaxation is mediated by NO and an apamin-sensitive mediator, and contraction primarily by acetylcholine. Despite the absence of c-Kit-positive ICC, nerve-muscle interaction can be accomplished likely by diffusion of neurotransmitters to the smooth muscle cells. The lack of c-Kit-positive ICC is related to an increase in the basal tone and spontaneous contractile activity. The presence of fibroblast-like ICC in Ws/Ws rats might represent immature ICC whose possible functions need further investigation.

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.

Ultrastructural injury to interstitial cells of Cajal and communication with mast cells in Crohn's disease

Crohn's disease associated dysmotility has been attributed to fibrosis and damage to enteric nerves but injury to interstitial cells of Cajal (ICC) could also be involved. We assessed ICC in specimens obtained from patients with Crohn's disease and determined the relation between ICC and the inflammatory infiltrate, particularly mast cells (MC) using quantitative immunohistochemistry and electron microscopy. Ultrastructural injury to ICC was patchy in all ICC subtypes but ICC-Auerbach's plexus (AP) showed damage more frequently, i.e. swelling of mitochondria, decreased electron density, autophagosomes and partial depletion of the cytoplasm. Light microscopy confirmed a significant decrease in c-kit immunoreactivity for ICC-AP and an increased number of MC in the muscularis externa. Electron microscopy showed MC exhibiting piecemeal degranulation and making frequent and selective membrane-to-membrane contact with all types of injured ICC which suggests chronic release of granule content to affect ICC. Extent of ICC injury was not associated with duration of the disease. In conclusion, ultrastructural injury and loss of ICC-AP is evident in Crohn's disease. Epidemiological and morphological data suggest that ICC have the capacity to regenerate in spite of the chronic insult. The muscularis hosts a marked number of MC that exhibit piecemeal degranulation associated with ICC and may facilitate ICC maintenance.

Unique distribution of interstitial cells of Cajal in the feline pylorus

The feline gastrointestinal (GI) tract is an important model for GI physiology but no immunohistochemical assessment of interstitial cells of Cajal (ICC) has been performed because of the lack of suitable antibodies. The aim of the present study was to investigate the various types of ICC and associated nerve structures in the pyloric sphincter region, by using immunohistochemistry and electron microscopy to complement functional studies. In the sphincter, ICC associated with Auerbach's plexus (ICC-AP) were markedly decreased within a region of 6-8 mm in length, thereby forming an interruption in this network of ICC-AP, which is otherwise continuous from corpus to distal ileum. In contrast, intramuscular ICC (ICC-IM) were abundant within the pylorus, especially at the inner edge of the circular muscle adjacent to the submucosa. Similar distribution patterns of nerves positive for vesicular acetylcholine transporter (VAChT), nitric oxide synthase (NOS) and substance P (SP) were encountered. Quantification showed a significantly higher number of ICC-IM and the various types of nerves in the pylorus compared with the circular muscle layers in the adjacent antrum and duodenum. Electron-microscopic studies demonstrated that ICC-IM were closely associated with enteric nerves through synapse-like junctions and with smooth muscle cells through gap junctions. Thus, for the first time, immunohistochemical studies have been successful in documenting the unique distribution of ICC in the feline pylorus. A lack of ICC-AP guarantees the distinct properties of antral and duodenal pacemaker activities. ICC-IM are associated with enteric nerves, which are concentrated in the inner portion of the circular muscle layer, being part of a unique innervation pattern of the sphincter.

Axial stretch: A novel mechanism of the lower esophageal sphincter relaxation

Swallow and esophageal distension-induced relaxations of the lower esophageal sphincter (LES) are associated with an orad movement of the LES because of a concurrent esophageal longitudinal muscle contraction. We hypothesized that the esophageal longitudinal muscle contraction induces a cranially directed mechanical stretch on the LES and therefore studied the effects of a mechanical stretch on the LES pressure. In adult opossums, a silicon tube was placed via mouth into the esophagus and laparotomy was performed. Two needles with silk sutures were passed, 90 degrees apart, through the esophageal walls and silicon tube, 2 cm above the LES. The tube was withdrawn, and one end of each of the four sutures was anchored to the esophageal wall and the other end exited through the mouth to exert graded cranially directed stretch on the LES by using pulley and weights. A cranially directed stretch caused LES relaxation, and with the cessation of stretch there was recovery of the LES pressure. The degree an d duration of LES relaxation increased with the weight and the duration of stretch, respectively. The mean LES relaxation in all animals was 77.7 +/- 4.7%. The required weight to induce maximal LES relaxation differed in animals (714 +/- 348 g). N(G)-nitro-L-arginine, a nitric oxide inhibitor, blocked the axial stretch-induced LES relaxation almost completely (from 78 to 19%). Our data support the presence of an axial stretch-activated inhibitory mechanism in the LES. The role of axial stretch in the LES relaxation induced by swallow and esophageal distension requires further investigation.

Interstitial cells of cajal are involved in neurotransmission in the gastrointestinal tract

Interstitial cells of Cajal (ICC) are important cells which coordinate gastrointestinal motility. ICC express Kit receptor tyrosine kinase, and Kit immunohistochemistry reveals ICC morphology and distribution in the gastrointestinal musculature. ICC show a highly branched morphology and form unique networks. Myenteric ICC (ICC-MY) are located at the layer of the myenteric plexus and serve as electrical pacemakers. Intramuscular ICC (ICC-IM) and ICC in the deep muscular plexus (ICC-DMP) are distributed within the muscular layers, and are densely innervated by excitatory and inhibitory enteric motor neurons and in close contact with nerve terminals. Recent studies combined with morphological and functional techniques directly revealed that ICC-IM and ICC-DMP are mediators of enteric motor neuro-transmission. These types of ICC express several receptors for neurotransmitters such as acetylcholine and substance P and show responses to excitatory nerve stimulations. ICC also express receptive mechanisms for nitric oxide, which is an inhibitory neurotransmitter in the gastrointestinal tract. They can respond to nitrergic nerve stimulation by cyclic GMP production. Kit mutant mice lack ICC-IM and show attenuated postsynaptic responses after intrinsic nerve stimulation. These findings indicate the importance for ICC in neurotransmission in the gastrointestinal tract.

Interstitial cells of Cajal and adaptive relaxation in the mouse stomach

Interstitial cells of Cajal (ICC) are proposed to play a role in stretch activation of nerves and are under intense investigation for potential roles in enteric innervation. Most data to support such roles come from in vitro studies with muscle strips whereas data at the whole organ level are scarce. To obtain insight into the role of ICC in distention-induced motor patterns developing at the organ level, we studied distension-induced adaptive relaxation in the isolated whole stomach of wild-type and W/W(v) mice. A method was developed to assess gastric adaptive relaxation that gave quantitative information on rates of pressure development and maximal adaptive relaxation. Pressure development was monitored throughout infusion of 1 ml of solution over a 10-min period. The final intraluminal pressure was sensitive to blockade of nitric oxide synthase, in wild-type and W/W(v) mice to a similar extent, indicating NO-mediated relaxation in W/W(v) mice. Adaptive relaxation occurred between 0.2 and 0.5 ml of solution infusion; this reflex was abolished by TTX, was not sensitive to blockade of nitric oxide synthase, but was abolished by apamin, suggesting that ATP and not nitric oxide is the neurotransmitter responsible for this intrinsic reflex. Despite the absence of intramuscular ICC (ICC-IM), normal gastric adaptive relaxation occurred in the W/W(v) stomach. Because pressure development was significantly lower in W/W(v) mice compared with wild type in all the conditions studied, including in the presence of TTX, ICC-IM may play a role in development of myogenic tone. In conclusion, a mouse model was developed to assess the intrinsic component of gastric accommodation. This showed that ICC-IM are not essential for activation of intrinsic sensory nerves nor ATP-driven adaptive relaxation nor NO-mediated relaxation in the present model. ICC-IM may be involved in regulation of (distention-induced) myogenic tone.

Kit mutants and gastrointestinal physiology

There has been considerable speculation about the function of interstitial cells of Cajal (ICC) since their discovery more than 100 years ago. It has been difficult to study these cells under native conditions, but great insights about the function of ICC have come from studies of genetic models with loss-of function mutations in the Kit signalling pathway. First it was discovered that signalling via Kit (a receptor tyrosine kinase) was vital for the development and maintenance of the ICC phenotype in gastrointestinal (GI) muscles. In compound heterozygotes (W/W(V) and Sl/Sl(d) animals), where there are partial loss-of-function mutations in Kit receptors or Kit ligand (stem cell factor), ICC failed to develop in various regions of the GI tract, but no major changes in the smooth muscle layers or enteric nervous system occurred in the absence of these cells. Animals with these mutations provided an unprecedented opportunity to understand the role of ICC in GI motor function, and it is now clear from these studies that ICC serve as: (i) pacemaker cells, generating the spontaneous electrical rhythms of the gut known as slow waves; (ii) a propagation pathway for slow waves so that large areas of the musculature can be entrained to a dominant pacemaker frequency; (iii) mediators of excitatory cholinergic and inhibitory nitrergic neural inputs from the enteric nervous system, and (iv) stretch receptors that modulate membrane potential and electrical slow wave frequency. This review describes the use of genetic models to understand the important physiological role of ICC in the GI tract.

A deficiency of gastric interstitial cells of Cajal accompanied by decreased expression of neuronal nitric oxide synthase and substance P in patients with type 2 diabetes mellitus

BACKGROUND

Gastrointestinal motility is impaired in patients with diabetes mellitus (DM). Interstitial cells of Cajal (ICC) in the gastrointestinal tract play a central role in gastrointestinal motility. The present study examined whether ICC density, or expression of neuronal nitric oxide synthase (nNOS)- and substance P (SP)-containing nerves in the gastric antrum, were altered in patients with type 2 DM.

METHODS

Paraffin-embedded gastric specimens from 51 controls and 36 male DM patients with gastric cancer were used for immunohistochemistry. Serial sections were stained with Kit and mast cell tryptase-specific antibodies. Fresh-frozen gastric specimens from patients with gastric cancer were used for immunofluorescence. The specimens were stained with antibodies to Kit, nNOS, and SP, and levels of expression of these three markers were compared between controls and DM patients.

RESULTS

ICC density in the inner circular muscle layer, but not in the myenteric plexus, was lower in patients with severe DM than in controls in paraffin-embedded specimens. In addition, decreased expression of nNOS and SP accompanied by reduced ICC density was observed in frozen specimens from patients with DM.

CONCLUSIONS

These results suggest that lower gastric ICC, nNOS, and SP densities in patients with DM may be associated with the pathogenesis of diabetic gastroparesis.

Loss of interstitial cells of Cajal network in severe idiopathic gastroparesis

AIM

To report a case of severe idiopathic gastroparesis in complete absence of Kit-positive gastric interstitial cells of Cajal (ICC).

METHODS

Gastric tissue from a patient with severe idiopathic gastroparesis unresponsive to medical treatment and requiring surgery was analyzed by conventional histology and immunohistochemistry.

RESULTS

Gastric pacemaker cells expressing Kit receptor had completely disappeared while the local level of stem cell factor, the essential ligand for its development and maintenance, was increased. No signs of cell death were observed in the pacemaker region.

CONCLUSION

These results are consistent with the hypothesis that a lack of Kit expression may lead to impaired functioning of ICC. Total gastrectomy proves to be curative.

Involvement of intramuscular interstitial cells of Cajal in neuroeffector transmission in the gastrointestinal tract

Specialized cells known as interstitial cells of Cajal (ICC) are distributed in specific locations within the tunica muscularis of the gastrointestinal (GI) tract. ICC serve as electrical pacemakers, provide pathways for the active propagation of slow waves, are mediators of enteric motor neurotransmission and play a role in afferent neural signalling. Morphological studies have provided evidence that motor neurotransmission in the GI tract does not occur through poorly defined structures between nerves and smooth muscle, but rather via specialized synapses that exist between enteric nerve terminals and intramuscular ICC or ICC-IM. ICC-IM are coupled to smooth muscle cells via gap junctions and post-junctional responses elicited in ICC-IM are conducted to neighbouring smooth muscle cells. Electrophysiological studies from the stomachs and sphincters of wild-type and mutant animals that lack ICC-IM have provided functional evidence for the importance of ICC in cholinergic excitatory and nitrergic inhibitory motor neurotransmission. Intraperitoneal injection of animals with Kit neutralizing antibody or organ culture of gastrointestinal tissues in the presence of neutralizing antibody, which blocks the development and maintenance of ICC, has provided further evidence for the role of ICC in enteric motor transmission. ICC-IM also generate an ongoing discharge of unitary potentials in the gastric fundus and antrum that contributes to the overall excitability of the stomach.

Structure and organization of interstitial cells of Cajal in the gastrointestinal tract

The morphological features of interstitial cells of Cajal (ICC) in the gastrointestinal (GI) tract are described based on observations of laboratory animals including mice, rats and guinea-pigs, using immunohistochemical staining for Kit and electron microscopy. ICC show a specific distribution, arrangement and cell shape depending on their location within various regions and tissue layers of the GI tract. Hence they are classified into several subtypes. The stomach shows distinct regional variations in the distribution of subtypes of ICC from the cardia to pylorus, whereas the small intestine and colon both seem to retain nearly the same distribution pattern of subtypes of ICC throughout each organ. All subtypes of ICC share common ultrastructural features, such as the presence of numerous mitochondria, abundant intermediate filaments, and formation of gap junctions with the same type of cells and with smooth muscle cells. In addition, depending on their species and anatomical location, some subtypes of ICC show some features typical of smooth muscle cells including a basal lamina, caveolae, subsurface cisterns and dense bodies. ICC are somewhat heterogeneous morphologically. A question is raised on a special relationship between their ultrastructural features and dependency on Kit/stem cell factor system. As the neuromediator function of ICC, reciprocal distribution of ICC and gap junctions in the muscle coat is demonstrated by the comparison of Kit immunoreactive cells and gap junction protein connexin 43 in both small intestine and colon.

Achalasia: physiology and etiopathogenesis

Achalasia is a disorder of esophageal motility that has been well documented for over 300 years. Despite this, the initiating factor or factors and the underlying mechanisms leading to the characteristic features of achalasia, the absence of distal esophageal peristalsis and abnormal lower esophageal sphincter relaxation, are still not well understood. Recent work has shed light on changes in neurotransmission and cell signaling in the lower esophagus and lower esophageal sphincter that lead to achalasia. A number of recent reviews have thoroughly discussed diagnostic and therapeutic modalities and the reader is referred to these for in-depth review of these topics. The focus of this review will be on our current understanding of the physiology of esophageal peristalsis and lower esophageal sphincter function as it relates to achalasia and on available evidence for etiology and proposed pathophysiologic mechanisms.

Intramuscular interstitial cells of Cajal associated with mast cells survive nitrergic nerves in achalasia

Achalasia is dominated by injury to inhibitory nerves. As intramuscular interstitial cells of Cajal (ICC-IM) are proposed to form functional units with nitrergic nerves, their fate in achalasia may be critically important. We studied the relationship between loss of nitrergic nerves and injury to ICC-IM in patients with achalasia and determined associations between ICC-IM and mast cells (MC), using quantitative immunohistochemistry and electron microscopy. Loss of neuronal nitric oxide synthase (nNOS) immunoreactivity was completed within 3 years of acquiring achalasia. Thereafter, progressive ultrastructural injury to remaining nerve structures was evident. Within the first 2 years, the number of ICC-IM did not decline although ultrastructural injury was already present. Thereafter, loss of ICC-IM occurred unrelated to duration of disease. Damage to ICC-IM appeared unrelated to nerve injury. A significant MC infiltration was observed in the musculature; the number of MC was positively related to the persistent number of ICC-IM. Mast cell formed close contacts with ICC-IM and piecemeal-degranulation occurred towards ICC-IM. In conclusion, injury to ICC-IM in achalasia is variable, but not related to duration of disease and injury to nitrergic nerves. MC are prominent and form close functional contact with ICC-IM which may be responsible for their relatively long survival.

Esophageal motor disorders: recent advances

PURPOSE OF REVIEW

The aim of this article is to highlight literature published during the last year in the context of previous knowledge.

RECENT FINDINGS

A number of novel techniques - high-resolution manometry, esophageal electrical impedance and intra-luminal ultrasound imaging - have improved our understanding of esophageal function in health and disease. Several studies address the function of longitudinal muscle layer of the esophagus in normal subjects and patients with motor disorders of the esophagus. Esophageal electrical impedance recordings reveal abnormal transit in patients with diffuse esophageal spasm, achalasia and patients with normal manometry. Loss of the mammalian Sprouty2 gene leads to enteric neuronal hyperplasia and esophageal achalasia. Several studies showed excellent long-term results of medical and surgical treatment of achalasia of the esophagus. For the first time, mechanisms of gastroesophageal reflux in critically ill mechanically ventilated patients are reported. Novel pharmacologic strategies in the treatment of reflux disease are highlighted.

SUMMARY

Several novel techniques, perfected during recent years, have improved our understanding of esophageal function and dysfunction. A number of important observations, reviewed here, provide important insight into the pathogenesis of esophageal motor disorders and treatment of gastroesophageal reflux disease.

Interstitial cells of cajal as pacemakers in the gastrointestinal tract

In the gastrointestinal tract, phasic contractions are caused by electrical activity termed slow waves. Slow waves are generated and actively propagated by interstitial cells of Cajal (ICC). The initiation of pacemaker activity in the ICC is caused by release of Ca2+ from inositol 1,4,5-trisphosphate (IP3) receptor-operated stores, uptake of Ca2+ into mitochondria, and the development of unitary currents. Summation of unitary currents causes depolarization and activation of a dihydropyridine-resistant Ca2+ conductance that entrains pacemaker activity in a network of ICC, resulting in the active propagation of slow waves. Slow wave frequency is regulated by a variety of physiological agonists and conditions, and shifts in pacemaker dominance can occur in response to both neural and nonneural inputs. Loss of ICC in many human motility disorders suggests exciting new hypotheses for the etiology of these disorders.

Control of intestinal motility by the Ca(v)1.2 L-type calcium channel in mice

The Ca(v)1.2 L-type Ca2+ channel is the dominant voltage-activated Ca2+ channel in heart and smooth muscle. The functional significance of this channel was studied in intestinal smooth muscle from mice carrying a smooth muscle-specific, conditional inactivation of the Ca(v)1.2 gene (Ca(v)1.2SMACKO mice). Inactivation was complete within 4 wk after tamoxifen treatment and confirmed by RT-PCR, Western blot and functional analysis. Ca(v)1.2SMACKO mice show reduced feces excretion, absence of rhythmic contractions in small and large intestinal muscle and signs of paralytic ileus. Extracellular field stimulation evoked smaller contractions in jejunum muscles from Ca(v)1.2SMACKO than from CTR mice, whereas carbachol-induced contractions of similar magnitude in both muscles. The Ca2+ needed for contraction in jejunum was provided mainly by Ca(v)1.2 channels and by store-operated channels in muscles from CTR and Ca(v)1.2SMACKO mice, respectively. In conclusion, the Ca(v)1.2 channel is essential for electromechanical coupling and important for pharmaco-mechanical coupling in intestinal smooth muscle and cannot be substituted functionally by other Ca2+ entry pathways.

Interstitial cells of Cajal in the urethra

The smooth muscle layer of the urethra generates spontaneous myogenic tone that is thought to make a major contribution to urinary continence. The mechanisms underlying generation of tone remain unclear, however recent studies from our laboratory highlighted a role for a specialised population of pacemaker cells which we originally referred to as interstitial cells (IC) and now term ICC. Urethra ICC possess an electrical pacemaker mechanism characterised by rhythmic activation of Ca(2+)-activated Cl(-) channels leading to spontaneous transient inward currents (STICs) under voltage clamp and spontaneous transient depolarisations (STDs) under current clamp conditions. Both STICS and STDs are now known to be associated with spontaneous Ca(2+) oscillations that result from a complex interplay between release of Ca(2+) from intracellular stores and Ca(2+) influx across the plasma membrane. In this review we will consider some of the precise mechanisms involved in the generation of pacemaker activity and discuss how these are modulated by excitatory and inhibitory neurotransmitters.

Interstitial cells of Cajal in the deep muscular plexus mediate enteric motor neurotransmission in the mouse small intestine

Interstitial cells of Cajal (ICC) provide important regulatory functions in the motor activity of the gastrointestinal tract. In the small intestine, ICC in the myenteric region (ICC-MY), between the circular and longitudinal muscle layers, generate and propagate electrical slow waves. Another population of ICC lies in the plane of the deep muscular plexus (ICC-DMP), and these cells are closely associated with varicose nerve terminals of enteric motor neurons. Here we tested the hypothesis that ICC-DMP mediate excitatory and inhibitory neural inputs in the small bowel. ICC-DMP develop largely after birth. ICC-DMP, with receptor tyrosine kinase Kit-like immunoreactivity, appear first in the jejunum and then in the ileum. We performed electrophysiological experiments on mice immediately after birth (P0) or at 10 days post partum (P10) to determine whether neural responses follow development of ICC-DMP. At P0, slow-wave activity was present in the jejunum, but neural responses were poorly developed. By P10, after ICC-DMP developed, both cholinergic excitatory and nitrergic inhibitory neural responses were intact. Muscles of P0 mice were also put into organotypic cultures and treated with a neutralizing Kit antibody. Neural responses developed in culture within 3-6 days in control muscles, but blocking Kit caused loss of ICC and loss of cholinergic and nitrergic neural responses. Non-cholinergic excitatory responses remained after loss of ICC-DMP. Our observations are consistent with the idea that cholinergic and nitrergic motor neural inputs are mediated, to a large extent, via ICC-DMP. Thus, ICC-DMP appear to serve a function in the small intestine that is similar to the role of the intramuscular ICC in the stomach.

Synaptic specializations exist between enteric motor nerves and interstitial cells of Cajal in the murine stomach

Autonomic neurotransmission is thought to occur via a loose association between nerve varicosities and smooth muscle cells. In the gastrointestinal tract ultrastructural studies have demonstrated close apposition between enteric nerves and intramuscular interstitial cells of Cajal (ICC-IM) in the stomach and colon and ICC in the deep muscular plexus (ICC-DMP) of the small intestine. In the absence of ICC-IM, postjunctional neural responses are compromised. Although membrane specializations between nerves and ICC-IM have been reported, the molecular identity of these specializations has not been studied. Here we have characterized the expression and distribution of synapse-associated proteins between nerve terminals and ICC-IM in the murine stomach. Transcripts for the presynaptic proteins synaptotagmin, syntaxin, and SNAP-25 were detected. Synaptotagmin and SNAP-25-immunopositive nerve varicosities were concentrated in varicose regions of motor nerves and were closely apposed to ICC-IM but not smooth muscle. W/W(V) mice were used to examine the expression and distribution of synaptic proteins in the absence of ICC-IM. Transcripts encoding synaptotagmin, syntaxin, and SNAP-25 were detected in W/W(V) tissues. In the absence of ICC-IM, synaptotagmin and SNAP-25 were localized to nerve varicosities. Reverse transcriptase polymer chain reaction (RT-PCR) and immunohistochemistry demonstrated the expression of postsynaptic density proteins PSD-93 and PSD-95 in the stomach and expression levels of PSD-93 and PSD-95 were reduced in W/W(V) mutants. These data support the existence of synaptic specializations between enteric nerves and ICC-IM in gastric tissues. In the absence of ICC-IM, components of the synaptic vesicle docking and fusion machinery is trafficked and concentrated in enteric nerve terminals.

Lower esophageal sphincter analysis using computerized manometry in patients with chagasic megaesophagus

Due to the introduction of computer technology into manometry laboratories, three-dimensional manometric images of the lower esophageal sphincter can be constructed based on radially oriented pressures, a method termed 'computerized axial manometry.' Calculation of the sphincter pressure vector volume using this method is superior to standard manometric techniques in assessing lower esophageal sphincter function in patients with gastroesophageal reflux disease and idiopathic achalasia. Despite similarities between idiopathic achalasia and chagasic esophagopathy found using clinical, radiological, and manometric studies, controversy around lower esophageal sphincter pressure persists. The goal of this study was to analyze esophageal motor disorders in Chagas' megaesophagus using computerized axial manometry. Twenty patients with chagasic megaesophagus (5 men, 15 women, and average age 50.1 years, range 17-64) were prospectively studied. For three-dimensional imaging construction of the lower esophageal sphincter, a low-complacency perfusion system and an eight-channel manometry probe with four radial channels placed in the same level were used. For probe traction, the continuous pull-through technique was used. Results showed that the lower esophageal sphincter of patients with chagasic megaesophagus have significantly elevated pressure, length, asymmetry, and vector volumes compared to those of normal volunteers (P < 0.05). Aperistalsis of the esophageal body waves was observed in all patients and contraction amplitude was lower than that in normal patients. We conclude that patients with chagasic megaesophagus have hypertonic lower esophageal sphincter and aperistalsis of the esophageal body.

Evolution of the diffuse neuroendocrine system--clear cells and cloudy origins

As early as the 2nd century, Galen proposed that 'vital spirits' in the blood regulated human bodily functions. However, the concept of hormonal activity required a further 18 centuries to develop and relied upon the identification of 'ductless glands', Schwann's cell and the recognition by Bayliss and Starling of chemical messengers. Bernard's introduction of 'internal secretion' and its role in homeostasis laid a physiological basis for the development of endocrinology. Kocher and Addison recognized the consequences of ablation of glands by disease or surgery and identified their necessary role in life. Detailed descriptions of the endocrine cells of the gut and pancreas and their putative function were provided by Heidenhain, Langerhans, Laguesse and Sharpey-Schafer. Despite the dominant 19th century concept of nervism (Pavlov), in 1902, Starling and Bayliss using Hardy's term 'hormonos' described secretin and in so doing, established the gut as an endocrine organ. Thus, nervism was supplanted by hormonal regulation of function and thereafter numerous bioactive gut peptides and amines were identified. At virtually the same time (1892), Ramón y Cajal of Madrid reported the existence of a group of specialized intestinal cells that he referred to as 'interstitial cells'. Cajal postulated that they might function as an interface between the neural system and the smooth muscles of the gut. Some 22 years later, Keith suggested that their function might be analogous to the electroconductive system of the heart and proposed their role as components of an intestinal pacemaker system. This prescient hypothesis was subsequently confirmed in 1982 by Thuneberg and a decade later Maede identified c-Kit as a critical molecular regulator in the development and function of the interstitial cells of Cajal and further confirmed the commonality of neural and endocrine cells. The additional characterization of the endocrine regulatory system of the GI tract was implemented when Feyrter (1938) using Masson's staining techniques, identified 'helle Zellen' within the pancreatic ductal system and the intestinal epithelium and proposed the concept of a diffuse neuroendocrine system. Pearse subsequently grouped the various cells belonging to that system under the rubric of a unifying APUD series. Currently, the gut neuroendocrine system is viewed as a syncytium of neural and endocrine cells sharing a common cell lineage whose phenotypic regulation is as yet unclear. Their key role in the regulation of gastrointestinal function is, however, indubitable.

Relationships between neurokinin receptor-expressing interstitial cells of Cajal and tachykininergic nerves in the gut

The so-called interstitial cells of Cajal (ICC) are distributed throughout the muscle coat of the alimentary tract with characteristic intramural location and species-variations in structure and staining. Several ICC sub-types have been identified: ICC-DMP, ICC-MP, ICC-IM, ICC-SM. Gut motility is regulated by ICC and each sub-type is responsible for the electrical activities typical of each gut region and/or muscle layer. The interstitial position of the ICC between nerve endings and smooth muscle cells has been extensively considered. Some of these nerve endings contain tachykinins. Three distinct tachykinin receptors (NK1r, NK2r and NK3r) have been demonstrated by molecular biology. Each of them binds with different affinities to a series of tachykinins (SP, NKA and NKB). In the ileum, SP-immunoreactive (SP-IR) nerve fibers form a rich plexus at the deep muscular plexus (DMP), distributed around SP-negative cells, and ICC-DMP intensely express the SP-preferred receptor NK1r; conversely a faint NK1r-IR is detected on the ICC-MP and mainly after receptor internalization was induced by agonists. ICC-IM are never stained in laboratory mammals, while those of the human antrum are NK1r- IR. RT-PCR conducted on isolated ileal ICC-MP and gastric ICC-IM showed that these cells express NK1r and NK3r. Colonic ICC, except those in humans, do not express NK1r-IR, at least in resting conditions. Outside the gut, NK1r-IR cells were seen in the arterial wall and exocrine pancreas. In the mouse gut only, NK1r-IR is present in non-neuronal cells located within the intestinal villi, so-called myoid cells, which are c-kit-negative and alpha-smooth muscle actin-positive. Immunohistochemistry and functional studies confirmed that ICC receive input from SP-IR terminals, with differences between ICC sub-types. In the rat, very early after birth, NK1r is expressed by the ICC-DMP and SP by the related nerve varicosities. Studies on pathological conditions are few and those on mutant strains practically absent. It has only been reported that in the inflamed ileum of rats the NK1r-IR ICC-DMP disappear and that at the peak of inflammatory conditions ICC-MP are NK1r-IR. In the ileum of mice with a mutation in the W locus, ICC-DMP were seen to express c-kit-IR but not NK1-IR, and SP-IR innervation seems unchanged. In summary, there are distinct ICC populations, each of them under a different tachykininergic control and, likely, having different functions. Further studies are recommended at the aim of understanding ICC involvement in modulating/transmitting tachykininergic inputs.

Lack of pyloric interstitial cells of Cajal explains distinct peristaltic motor patterns in stomach and small intestine

The frequency and propagation velocity of distension-induced peristaltic contractions in the antrum and duodenum are distinctly different and depend on activation of intrinsic excitatory motoneurons as well as pacemaker cells, the interstitial cells of Cajal associated with Auerbach's plexus (ICC-AP). Because ICC are critical for coordination of motor activities along the long axis of many regions in the gut, the role of ICC in antroduodenal coordination was investigated. We used immunohistochemistry, electron microscopy, simultaneous multiple electrical recordings in vitro, and videofluoroscopy in vivo in mice and rats. A strongly reduced number of ICC-AP with loss of network characteristics was observed in a 4-mm area in the rat and a 1-mm area in the mouse pyloric region. The pyloric region showed a slow wave-free gap of 4.1 mm in rats and 1.3 mm in mice. Between antrum and duodenum, there was no interaction of electrical activities and in the absence of gastric emptying, there was no coordination of motor activities. When the pyloric sphincter opened, 2.4 s before the front of the antral wave reached the pylorus, the duodenum distended after receiving gastric content and aboral duodenal peristalsis was initiated, often disrupting other motor patterns. The absence of ICC-AP and slow wave activity in the pyloric region allows the antrum and duodenum to have distinct uncoordinated motor activities. Coordination of aborally propagating peristaltic antral and duodenal activity is initiated by opening of the pylorus, which is followed by distention-induced duodenal peristalsis. Throughout this coordinated motor activity, the pacemaker systems in antrum and duodenum remain independent.

Gastrointestinal function regulation by nitrergic efferent nerves

Gastrointestinal (GI) smooth muscle responses to stimulation of the nonadrenergic noncholinergic inhibitory nerves have been suggested to be mediated by polypeptides, ATP, or another unidentified neurotransmitter. The discovery of nitric-oxide (NO) synthase inhibitors greatly contributed to our understanding of mechanisms involved in these responses, leading to the novel hypothesis that NO, an inorganic, gaseous molecule, acts as an inhibitory neurotransmitter. The nerves whose transmitter function depends on the NO release are called "nitrergic", and such nerves are recognized to play major roles in the control of smooth muscle tone and motility and of fluid secretion in the GI tract. Endothelium-derived relaxing factor, discovered by Furchgott and Zawadzki, has been identified to be NO that is biosynthesized from l-arginine by the constitutive NO synthase in endothelial cells and neurons. NO as a mediator or transmitter activates soluble guanylyl cyclase and produces cyclic GMP in smooth muscle cells, resulting in relaxation of the vasculature. On the other hand, NO-induced GI smooth muscle relaxation is mediated, not only by cyclic GMP directly or indirectly via hyperpolarization, but also by cyclic GMP-independent mechanisms. Numerous cotransmitters and cross talk of autonomic efferent nerves make the neural control of GI functions complicated. However, the findingsrelated to the nitrergic innervation may provide us a new way of understanding GI tract physiology and pathophysiology and might result in the development of new therapies of GI diseases. This review article covers the discovery of nitrergic nerves, their functional roles, and pathological implications in the GI tract.

Severe gastrointestinal dysmotility in a patient with congenital myopathy: causal relationship to decrease of interstitial cells of Cajal

Interstitial cells of Cajal (ICC) are known to be essential regulators of gastrointestinal (GI) motility. Here, we report the clinical course and abnormalities of intestinal ICC distribution in a 5-year-old patient with congenital fiber type disproportion myopathy who demonstrated long-term GI dismotility. Full thickness biopsies of the small intestine and colon showed a normal enteric muscle layer and myenteric plexus. However, the density of ICC was strikingly decreased around the myenteric plexus compared to that in autopsied cases without GI tract disease. These findings suggest that a decline in ICC may contribute to disturbed GI motility in our patient with congenital myopathy.

Ascending contraction and descending relaxation in the distal colon of mice lacking interstitial cells of Cajal

Recently an essential role of interstitial cells of Cajal (ICC) within myenteric plexus (ICC-MY) was suggested in ascending contraction and descending relaxation in the mouse ileum. The role of ICC in these neural reflexes was examined in the distal colonic segments prepared from the wild type and c-kit mutant, W/W(V) mice, in the present study. Localized distension of the segments from the wild type mice by using a small balloon resulted in ascending contraction and descending relaxation. In the segments from the mutant mice, localized distension also induced these neural reflexes similar to those observed in the wild type mice. Immunohistochemical examination demonstrated that ICC-MY and ICC present in muscle layers (ICC-IM) were severely disrupted in the mutant mouse, but only ICC, present within submucosal plexus (ICC-SMP), remained unchanged. In the small strips with ICC-SMP absent prepared from the mutant mouse, electrical field stimulation induced contraction or relaxation in the absence or presence of atropine, respectively. It was suggested that ICC have no important role in the ascending and descending neural reflexes in the mouse distal colon, this is in direct contrast to the role of ICC-MY in the ileum.

Distinct roles of nitric oxide synthases and interstitial cells of Cajal in rectoanal relaxation

Nitric oxide (NO) relaxes the internal anal sphincter (IAS), but its enzymatic source(s) remains unknown; neuronal (nNOS) and endothelial (eNOS) NO synthase (NOS) isoforms could be involved. Also, interstitial cells of Cajal (ICC) may be involved in IAS relaxation. We studied the relative roles of nNOS, eNOS, and c-Kit-expressing ICC for IAS relaxation using genetic murine models. The basal IAS tone and the rectoanal inhibitory reflex (RAIR) were assessed in vivo by a purpose-built solid-state manometric probe and by using wild-type, nNOS-deficient (nNOS-/-), eNOS-deficient (eNOS-/-), and W/W(v) mice (lacking certain c-Kit-expressing ICC) with or without L-arginine or N(omega)-nitro-L-arginine methyl ester (L-NAME) treatment. Moreover, the basal tone and response to electrical field stimulation (EFS) were studied in organ bath using wild-type and mutant IAS. In vivo, the basal tone of eNOS-/- was higher and W/W(v) was lower than wild-type and nNOS-/- mice. L-arginine administered rectally, but not intravenously, decreased the basal tone in wild-type, nNOS-/-, and W/W(v) mice. However, neither L-arginine nor L-NAME affected basal tone in eNOS-/- mice. In vitro, L-arginine decreased basal tone in wild-type and nNOS-/- IAS but not in eNOS-/- or wild-type IAS without mucosa. The in vivo RAIR was intact in wild-type, eNOS-/-, and W/W(v) mice but absent in all nNOS-/- mice. EFS-induced IAS relaxation was also reduced in nNOS-/- IAS. Thus the basal IAS tone is largely controlled by eNOS in the mucosa, whereas the RAIR is controlled by nNOS. c-Kit-expressing ICC may not be essential for the RAIR.

In vivo gastric and intestinal slow waves in W/WV mice

The aim was to investigate whether there are regular gastric and intestinal slow waves in conscious W/WV mice. Eleven W/WV mice and 11 wild-type mice were implanted with two pairs of electrodes in the stomach and small intestine. Gastrointestinal slow waves were recorded both under anesthesia and in the conscious state. Atropine and verapamil were given separately to an additional 10 W/WV mice. Results were as follows. (1) The conscious W/WV mice showed lower rhythmic slow waves in the small intestine (77.1 vs 93.5%; P < 0.001). However, the frequency (10.7 vs 18.8 cpm; P < 0.0001) and the antregrade propagation of intestinal slow waves in W/Wv mice were significantly lower than in the controls. In the stomach, regular slow waves were recorded in both groups, with no difference between the two groups. (2) Anesthesia significantly impaired both gastric and intestinal slow waves in both groups. (3) Atropine and verapamil had no effects on the rhythmicity of intestinal slow waves. We conclude that ICC-MY may not be the sole pacemaker cells for slow waves in the small intestine. There may be some abnormality of smooth muscle cells in W/WV mice that causes a reduction in the frequency, rhythmicity, and antegrade propagation of slow waves.

CaM kinase II and phospholamban contribute to caffeine-induced relaxation of murine gastric fundus smooth muscle

Caffeine has been shown to increase the Ca2+release frequency (Ca2+sparks) from the sarcoplasmic reticulum (SR) through ryanodine-sensitive stores and relax gastric fundus smooth muscle. Increased Ca2+store refilling increases the frequency of Ca2+release events and store refilling is enhanced by CaM kinase II (CaMKII) phosphorylation of phospholamban (PLB). These findings suggest that transient, localized Ca2+release events from the SR may activate CaMKII and contribute to relaxation by enhancing store refilling due to PLB Thr17 phosphorylation. To investigate this possibility, we examined the effects of caffeine on CaMKII, muscle tone, and PLB phosphorylation in murine gastric fundus smooth muscle. Caffeine (1 mM) hyperpolarized and relaxed murine gastric fundus smooth muscle and activated CaMKII. Ryanodine, tetracaine, or cyclopiazonic acid each prevented CaMKII activation and significantly inhibited caffeine-induced relaxation. The large-conductance Ca2+-activated K+channel blocker iberiotoxin, but not apamin, partially inhibited caffeine-induced relaxation. Caffeine-induced CaMKII activation increased PLB Thr17, but not PLB Ser16 phosphorylation. 3-Isobutyl-1-methylxanthine increased PLB Ser16 phosphorylation, but not PLB Thr17 phosphorylation. The CaMKII inhibitor KN-93 inhibited caffeine-induced relaxation and PLB Thr17 phosphorylation. These results show that caffeine-induced CaMKII activation and PLB phosphorylation play a role in the relaxation of gastric fundus smooth muscles.

The internal anal sphincter: regulation of smooth muscle tone and relaxation

Basal tone in the internal anal sphincter (IAS) is primarily myogenic. Neurohumoral substances like angiotensin II may partially provide external signal for the basal tone in the IAS. The sphincteric relaxation on the contrary is neurogenic by activation of non-adrenergic non-cholinergic (NANC) nerves that release nitric oxide (NO), vasoactive intestinal polypeptide (VIP) and perhaps carbon monoxide. Because of the presence of spontaneous tone, the IAS offers an excellent model to investigate the nature of the inhibitory neurotransmission for NANC relaxation. Work from different laboratories in different species concludes that NO is the major contributor in the NANC relaxation. This may invoke the role of other inhibitory neurotransmitters such as VIP, working partly via NO. An understanding of the basic regulation of basal tone in the IAS and nature of inhibitory neurotransmission are critical in the pathophysiology and therapeutic potentials in the anorectal motility disorders.

Reduced insulin and IGF-I signaling, not hyperglycemia, underlies the diabetes-associated depletion of interstitial cells of Cajal in the murine stomach

Damage to interstitial cells of Cajal (ICC), pacemakers, and mediators of neuromuscular neurotransmission in the gastrointestinal tract contributes to the pathogenesis of diabetic gastroenteropathy in both patients and animal models. ICC depletion in diabetes may result from chronic hyperglycemia or lost/ineffective insulin signaling. Because independent control of insulin and glucose concentrations is difficult in chronic in vivo studies, we used long-term organotypic cultures to address this problem. Murine gastric muscles were cultured in normoglycemic or hyperglycemic basal media with or without insulin or IGF-I for 1-3 months, the time required for gastroparesis and ICC damage to develop in diabetic mice. ICC were assessed by c-Kit immunohistochemistry and quantitative analysis of c-kit expression. Electrical pacemaking was studied by intracellular recording of slow waves. ICC survived for at least 34 days in unsupplemented normoglycemic media, but their networks, c-kit expression, and slow waves were profoundly reduced after 68 days. These changes could be entirely prevented by insulin or IGF-I supplementation. ICC networks were completely resistant to hyperglycemia for at least 72 days. Thus, hyperglycemia is unlikely to be responsible for the diabetes-associated depletion of ICC. In contrast, maintenance of ICC requires insulin or IGF-I, which are reduced or ineffective in diabetes.

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.

Regional variation in ICC distribution, pacemaking activity and neural responses in the longitudinal muscle of the murine stomach

Intramuscular interstitial cells of Cajal (ICC-IM) play a critical role in enteric neural regulation of the circular muscle layer in the stomach, but no studies have been performed on the longitudinal layer. Kit immunohistochemistry was used to examine ICC-IM in the longitudinal muscle layer of the murine corpus and antrum, and it revealed marked heterogeneity in the distribution of ICC-IM in longitudinal muscles. In the corpus, ICC-IM were found along the greater curvature near the fundus. ICC-IM decreased in density in the circumferential axis toward the lesser curvature and in the longitudinal axis toward the antrum. ICC-IM were absent from the longitudinal layer of the antrum. Double labelling with markers for specific classes of enteric motor neurones revealed that cholinergic and nitrergic motor neurones formed close contacts with ICC-IM in the corpus but not in the antrum. Enteric nerve stimulation evoked prominent cholinergic excitatory and nitrergic inhibitory responses in longitudinal muscles of the corpus, but not in the antrum of wild-type animals. Cholinergic and nitrergic nerves were also present in W/W(V) mice, but functional innervation of the longitudinal muscle layer by these nerves in the corpus and antrum were absent. The data show that cholinergic and nitrergic neurotransmission only occurs in the gastric longitudinal layer in regions where ICC-IM are present. In regions, such as the corpus, where ICC-IM are common, robust neural responses are present, but the reduced density of ICC-IM near the lesser curvature and in the distal stomach leads to reduced neural regulation in these gastric regions.

Essential role of the interstitial cells of Cajal in nitric oxide-mediated relaxation of longitudinal muscle of the mouse ileum

The role of interstitial cells of Cajal (ICC) in electrical field stimulation (EFS)-induced neurogenic responses in ileum was studied by using the ICC-deficient mutant (SLC-W/W(V)) mouse and its wild type. In the immunohistochemical study with anti-c-Kit antibody, ICC was observed in the myenteric plexus (MY) and deep muscular plexus (DMP) region in the wild type. In the mutant, ICC-MY were lost, only ICC-DMP were present. EFS induced a rapid contraction of the ileal segments from the wild type mouse in the direction of longitudinal muscle. In the mutant mouse, onset of contraction was delayed and its rate was slowed. EFS induced nonadrenergic, noncholinergic (NANC) relaxation in the presence of atropine and guanethidine in the wild type. A nitric oxide synthase inhibitor inhibited the relaxation and L-arginine reversed it. In the mutant, EFS did not induce NANC relaxation. There was no difference between the responsiveness of the segments from wild type and mutant mice to exogenously added acetylcholine or Nor-1. Taking into account the selective loss of ICC-MY in the mutant mice, it seems likely that ICC-MY have an essential role in inducing nitric oxide-mediated relaxation of longitudinal muscle of the mouse ileum and that ICC-MY partly participate in EFS-induced contraction.

Role of the interstitial cells distributed in the myenteric plexus in neural reflexes in the mouse ileum

We examined the role of interstitial cells of Cajal (ICC) in the ascending and descending neural reflexes in the ileal segments prepared from wild type mice and c-kit mutant W/WV mice. Localized distension of the ileal segments from wild type mice with a small balloon caused contraction or relaxation of the circular muscle on the oral or anal side of the distended region, respectively. However, these intestinal reflexes were not induced in the ileal segments from the mutant mice. In the small strips that include the step of the pathways from efferent motor neurons to smooth muscle cells, nerve stimulation induced contraction of circular muscle in the absence of atropine and relaxation in the presence of atropine. The extent of nerve stimulation-induced contractions and relaxations of the ileal circular muscle were similar in wild type and W/WV mice. The responsiveness of ileal circular muscle to exogenously added acetylcholine and Nor-1, a nitric oxide donor, was also unaffected in the mutant ileum. Since previous immunohistochemical study had revealed selective loss of ICC within the myenteric plexus (ICC-MY) in the mutant ileum, it was concluded that ICC-MY have an essential role in ascending and descending neural pathways in the mouse ileum.

Constitutive and functional expression of cyclooxygenase 2 in the murine proximal colon

Recent reports suggest that cyclo-oxygenase (COX)-2, an inducible COX isoform may be constitutively expressed in gastrointestinal tissues. This study has evaluated the expression and function of COX-2 in the tunica muscularis of the murine proximal colon. Cyclo-oxygenase-2-like (COX-2-LI) immunoreactivity was found in a subpopulation of neurones in the myenteric and submucosal ganglia and in interstitial cells of Cajal within the muscle layers (IC-IM). Reverse transcriptase polymerase chain reaction (RT-PCR) verified expression of COX-2 in colonic muscles, and quantitative PCR demonstrated that COX-1 transcriptional expression was greater than COX-2. To test the functional significance of COX-2 expression, the effects of a COX-2 inhibitor were compared with the effects of indomethacin (COX-1/COX-2 inhibitor) on circular muscle contractions. The experiments indicate that indomethacin and the specific COX-2 inhibitor, GR253035X, increased the amplitude of phasic contractions, suggesting production of inhibitory prostaglandins tonically dampen contractile activity. The effects of indomethacin were reduced when tested on phasic contractions of muscles from COX-2 knockout mice. GR253035X did not affect contractions in muscles of COX-2 knockout animals. These studies demonstrate constitutive expression of COX-2 in the tunica muscularis of the proximal colon. The COX-2 appears to contribute a significant amount of the prostaglandins that affect the contractile behaviour of colonic muscles.

Identification of interstitial cells of Cajal in corporal tissues of the guinea-pig penis

This study shows for the first time the presence of interstitial cells of Cajal (ICC) and their possible role in the initiation of spontaneous excitation in the corporal tissue of the guinea-pig penis. ICC, which were identified by their c-kit immunoreactivity, were abundantly distributed in the corporal smooth muscle meshwork. Spontaneous increases in the intracellular calcium concentration ([Ca(2+)](i); calcium transients) were visualized in preparations loaded with the fluorescent dye fura-2. Ca transients originated from the boundary of muscle bundles and then spread throughout the meshwork (Ca waves). Ca waves were strongly suppressed by either CPA (10 microm), ryanodine (50 microm) or 2-APB (10 microm), and their synchronicity was disrupted by 18beta-GA (30 microm). These results suggest that ICC in the corporal tissue may have a role as pacemakers to drive the bulk of smooth muscles, and that intracellular Ca(2+) stores and gap junctions are critical for the generation of spontaneous excitation.

Vimentin-positive, c-kit-negative interstitial cells in human and rat uterus: a role in pacemaking?

The mechanism underlying spontaneous pacemaker potential in the uterus is not clearly understood. Several spontaneously active smooth muscles have interstitial cells of Cajal (ICCs) or ICC-like cells. We therefore examined cells from freshly dispersed uterine muscle strips (from pregnant human and rat myometrium) and in situ uterine preparations to determine the cell types present. Both preparations revealed numerous ICC-like cells; they were multipolar, with spider-like projections and enlarged central regions. These cells were readily distinguished from uterine myocytes by their morphology and ultrastructure, i.e., no myofilaments, numerous mitochondria, caveolae, and filaments. In addition, the ICC-like cells were noncontractile. These cells were negative to c-kit, a classic marker for ICCs. They stained positive for the intermediate filament, vimentin, a marker for cells of mesenchymal origin but not differentiated myocytes. The ICC-like cells had a more or less stable resting membrane potential of -58+/-7 mV compared with smooth-muscle cells, -65+/-13 mV, and produced outward current in response to voltage clamp pulses. However, in contrast with uterine myocytes, inward currents were not observed. This is the first description of ICC-like cells in myometrium and their role in the uterus is discussed, as possible inhibitors of intrinsic smooth-muscle activity.

Esophageal muscle physiology and morphogenesis require assembly of a collagen XIX-rich basement membrane zone

Collagen XIX is an extremely rare extracellular matrix component that localizes to basement membrane zones and is transiently expressed by differentiating muscle cells. Characterization of mice harboring null and structural mutations of the collagen XIX (Col19a1) gene has revealed the critical contribution of this matrix protein to muscle physiology and differentiation. The phenotype includes smooth muscle motor dysfunction and hypertensive sphincter resulting from impaired swallowing-induced, nitric oxide–dependent relaxation of the sphincteric muscle. Muscle dysfunction was correlated with a disorganized matrix and a normal complement of enteric neurons and interstitial cells of Cajal. Mice without collagen XIX exhibit an additional defect, namely impaired smooth-to-skeletal muscle cell conversion in the abdominal segment of the esophagus. This developmental abnormality was accounted for by failed activation of myogenic regulatory factors that normally drive esophageal muscle transdifferentiation. Therefore, these findings identify collagen XIX as the first structural determinant of sphincteric muscle function, and as the first extrinsic factor of skeletal myogenesis in the murine esophagus.

Electrophysiological properties of inhibitory junction potential in murine lower oesophageal sphincter

The electrophysiological properties of smooth muscle in the murine lower oesophageal sphincter (LOS) were investigated by intracellular microelectrode recording. Inhibitory junction potentials (IJPs) evoked by trains of field stimulation (30 V, 0.2-0.3 ms, 10 stimuli at 1-50 Hz) were observed in the murine LOS in the presence of atropine (1 microM) and nifedipine (1 microM). The IJP consists of two components, which we termed fast IJP and slow IJP. The fast IJP was partly sensitive to guanethidine (5 microM), pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS, 30 microM) and apamin (0.1 microM), suggesting that the fast IJP was produced partly through the activation of apamin-sensitive Ca2+-activated K+ channels and of P2-purinoceptors. The other part of the fast IJP was sensitive to N(omega)-nitro-L-arginine (L-NNA, 100 microM) and 1H-[1,2,4]oxadiazolo[4,3-a]quinoxaline-1-one (ODQ, 1 microM), but insensitive to apamin (0.1 microM), iberiotoxin (50 nM) and charybdotoxin (30 nM). Slow IJP was sensitive to L-NNA (100 microM), ODQ (10 microM) and glibenclamide (10 microM), but insensitive to apamin (0.1 microM), iberiotoxin (50 nM) and charybdotoxin (30 nM). KT5823, a protein kinase G (PKG) inhibitor, had no effect on the fast and slow IJP in this tissue. It was suggested that, in the mouse LOS, adenosine trisphosphate (ATP) partly mediated the fast UP through apamin-sensitive Ca2+-activated K+ channels, and nitric oxide mediated the remained part of the fast IJP and the slow IJP through cGMP, but not PKG. ATP-sensitive K+ channels were suggested to be partly involved in the production of slow IJP, but the responsible channel(s) for the nitrergic fast IJP remained unclarified.

Gut pacemaker cells: the interstitial cells of Cajal (ICC)

This review will focus on the pacemaker mechanisms underlying gastrointestinal autonomic rhythmicity in an attempt to elucidate the differences and similarities between the pacemaker mechanisms in the heart and gut. Interstitial cells of Cajal (ICC) form networks that are widely distributed within the submucosal (ICC-SM), intra-muscular (ICC-IM, ICC-DMP) and inter-muscular layers (ICC-MY) of the gastrointestinal tract from the esophagus to the internal anal sphincter. The ICC generate spontaneously active pacemaker currents that may be recorded as plateau and slow potentials. These pacemaker currents drive the spontaneous electrical and mechanical activities of smooth muscle cells. The enteric nervous system, composed of both the myenteric (inter-muscular) plexus and the submucosal plexus, is also distributed in the gastrointestinal tract from the esophagus to the internal anal sphincter. The role of the ICC and the enteric nervous system in the integrative control of gastrointestinal function and especially of spontaneous rhythmic activity, is still unknown. Nevertheless, at least from the results presented in this review of studies of the jejunum, ileum and proximal colon of the mouse, it is convincing that the ICC drive spontaneous rhythmic motility, although a role for the enteric nervous system in the regulation of spontaneous rhythmic motility cannot be overlooked. Furthermore, intracellular Ca2+ handling has a critical role in the generation of pacemaker activity in the gut and heart, although respective players such as the Ca2+-ATPase of the sarcoplasmic reticulum (endoplasmic reticulum), IP3 receptors, ryanodine receptors and plasma membrane ion channels may have divergent roles in the Ca2+-release refilling cycles. In conclusion, intracellular Ca2+ handling plays a key role in the gut pacemaker responsible for spontaneous rhythmicity, as well as in the cardiac pacemaker responsible for spontaneous beating. Pharmacotherapeutic targeting of intracellular Ca2+ handling mechanisms may be a promising approach to the treatment and cure of gut motility dysfunction.