Ultrastructural localization of neuronal nitric oxide synthase-immunoreactivity in the rat ileum

Nitric Oxide Is Essential for Generating the Minute Rhythm Contraction Pattern in the Small Intestine, Likely via ICC-DMP

Nitrergic nerves have been proposed to play a critical role in the orchestration of peristaltic activities throughout the gastrointestinal tract. In the present study, we investigated the role of nitric oxide, using spatiotemporal mapping, in peristaltic activity of the whole ex vivo mouse intestine. We identified a propulsive motor pattern in the form of propagating myogenic contractions, that are clustered by the enteric nervous system into a minute rhythm that is dependent on nitric oxide. The cluster formation was abolished by TTX, lidocaine and nitric oxide synthesis inhibition, whereas the myogenic contractions, occurring at the ICC-MP initiated slow wave frequency, remained undisturbed. Cluster formation, inhibited by block of nitric oxide synthesis, was fully restored in a highly regular rhythmic fashion by a constant level of nitric oxide generated by sodium nitroprusside; but the action of sodium nitroprusside was inhibited by lidocaine indicating that it was relying on neural activity, but not rhythmic nitrergic nerve activity. Hence, distention-induced activity of cholinergic nerves and/or a co-factor within nitrergic nerves such as ATP is also a requirement for the minute rhythm. Cluster formation was dependent on distention but was not evoked by a distention reflex. Block of gap junction conductance by carbenoxolone, dose dependently inhibited, and eventually abolished clusters and contraction waves, likely associated, not with inhibition of nitrergic innervation, but by abolishing ICC network synchronization. An intriguing feature of the clusters was the presence of bands of rhythmic inhibitions at 4-8 cycles/min; these inhibitory patches occurred in the presence of tetrodotoxin or lidocaine and hence were not dependent on nitrergic nerves. We propose that the minute rhythm is generated by nitric oxide-induced rhythmic depolarization of the musculature via ICC-DMP.

Ultrastructural and Immunohistochemical Features of Telocytes in Placental Villi in Preeclampsia

A new cell type, interstitial Cajal-like cell (ICLC), was recently described in different organs. The name was recently changed to telocytes (TCs), and their typical thin, long processes have been named telopodes (Tp). TCs regulate the contractile activity of smooth muscle cells and play a role in regulating vessel contractions. Although the placenta is not an innervated organ, we believe that TCs are present in the placenta. We studied placenta samples from physiological pregnancies and in different variants of preeclampsia (PE). We examined these samples using light microscopy of semi-thin sections, transmission electron microscopy, and immunohistochemistry. Immunohistochemical examination was performed with primary antibodies to CD34, CD117, SMA, and vimentin, and TMEM16a (DOG-1), the latter was used for the diagnosis of gastrointestinal stromal tumours (GIST) consisting of TCs. We have identified a heterogenetic population of ТСs in term placentas, as these cell types differed in their localization, immunophenotype and ultrastructural characteristics. We assume TMEM16a could be used as the marker for identification of TCs. In PE we have revealed telocyte-like cells with ultrastructural signs of fibrocytes (significant process thickening and the granular endoplasmic reticulum content was increased) and a loss of TMEM16a immunohistochemical staining.

Non-adrenergic non-cholinergic inhibition of gastrointestinal smooth muscle and its intracellular mechanism(s)

Relaxation of gastrointestinal smooth muscle caused by release of non-adrenergic non-cholinergic (NANC) transmitters from enteric nerves occurs in several physiologic digestive reflexes. Likely candidate NANC inhibitory agents include nitric oxide (NO), adenosine triphosphate (ATP), vasoactive intestinal peptide (VIP), pituitary adenylate cyclase-activating peptide (PACAP), carbon monoxide (CO), protease-activated receptors (PARs), hydrogen sulfide (H2S), neurotensin (NT) and beta-nicotinamide adenine dinucleotide (beta-NAD). Multiple NANC transmitters work in concert, are pharmacologically coupled and are closely coordinated. Individual contribution varies regionally in the gastrointestinal tract and between species. NANC inhibition of gastrointestinal smooth muscle involves several intracellular mechanisms, including increase of cyclic guanosine monophosphate (cGMP), increase of cyclic adenosine monophosphate (cAMP) and hyperpolarization of the cell membrane via direct or indirect activation of potassium ion (K+) channels.

Mechanisms of relaxation by carbon monoxide-releasing molecule-2 in murine gastric fundus and jejunum

This study investigated the effects and mechanisms of action of carbon monoxide-releasing molecule-2 (CORM-2), compared to those of carbon monoxide (CO), in murine gastric fundus and jejunal circular smooth muscle. Functional in vitro experiments and cGMP measurements were conducted. In both tissues, CO and CORM-2 induced concentration-dependent relaxations. CO-induced relaxations were abolished by the soluble guanylyl cyclase (sGC) inhibitor ODQ, while CORM-2-evoked inhibitory responses were only partly prevented by ODQ. Relaxations elicited by CO (300 microM) were associated with a significant increase in cGMP levels, whereas for CORM-2 (300 microM) no significant increase in cGMP levels could be measured. The sGC sensitizer YC-1 was able to accelerate and potentiate both CO- and CORM-2-induced relaxations. Furthermore, the intermediate- and large-conductance Ca2+-activated K+ (IKCa-BKCa) channel blocker charybdotoxin significantly reduced CO- and CORM-2-induced relaxations in jejunal tissue; this same effect was observed with the BKCa channel blocker iberiotoxin. The combination of apamin plus charybdotoxin significantly reduced relaxations in gastric fundus and had synergistic inhibitory effects in jejunum. The NOS inhibitor L-NAME had no effect on the induced relaxations in gastric fundus, but significantly reduced CO- and CORM-2-evoked relaxations in jejunum. In conclusion, these results demonstrate that CO and CORM-2 produce relaxation in gastric fundus and jejunum via sGC and activation of KCa channels, and a nitric oxide (NO)-mediated amplification of CO signaling in jejunum is suggested.

Substance P and Neurokinin 1 receptor - expression is affected in the ileum of mice with mutation in the W locus

The tachykinin substance P (SP) acts on the gut muscle coat via its preferred receptor, neurokinin 1 (NK1r). In the mouse ileum, NK1r-immunoreactivity (NK1r-IR) was detected in neurons, in the interstitial cells of Cajal at the deep muscular plexus (ICC-DMP) and the myoid cells of the villi. SP-IR was detected in neurons and varicose nerve fibers, which were especially numerous at the DMP and closely associated with the ICC-DMP. In mice with a mutation in the W locus (ckit mutant animals), innervation is suggested to be normal although few studies have actually tested this hypothesis. Indeed, studies demonstrating ICC-DMP integrity are lacking and whether SP- and NK1r-IR are normal in these animals has not been investigated. Our aim was to perform an immunohistochemical study on the ileum of a strain of heterozygous mice with a mutation in the W locus, the W(e/+) mice, to test this hypothesis. SP-IR nerve fibers were significantly more numerous than in wild type mice; NK1r-IR was clustered on the plasma membrane and also intracytoplasmatic in the neurons, but absent in the ICC-DMP. The richness in SP-IR nerve fibers and the NK1r-IR distribution in the neurons, similar to that of activated cells, might be attempts to compensate for the SP preferred receptor absence at the ICC-DMP. In conclusion, SP content and NK1r expression are noticeably different in c-kit mutants with respect to wild type mice, and probably causing an anomalous tachykininergic control of intestinal motility. Physiological studies on Wmutant mice have to take into account that innervation in this animal model is affected by the c-kit mutation.

Enteric neuropathology of the terminal ileum in patients with intractable slow-transit constipation

Slow-transit constipation is usually considered a colonic motor disorder. However, there is some evidence that abnormalities may be present in locations other than the colon. In particular, several studies have reported abnormal motor activity of the small bowel in these patients. We evaluated the neuropathological aspects of the terminal ileum in patients with slow-transit constipation to see whether abnormalities are present that may explain an abnormal motility of the small intestine. Specimens of the terminal ileum were obtained from 16 female patients (age range, 42-76 years) with slow-transit constipation undergoing surgery for intractable symptoms. Fifteen age- and sex-matched controls were used for comparison. Histologic and immunohistochemical evaluation of the myenteric plexus and the smooth muscle of the proximal ileal resection margin was carried out by means of hematoxylin and eosin, trichrome and periodic acid-Schiff stain, neuron-specific enolase, S-100, CD117, CD34, anti-alpha-actin, desmin, and vimentin antibodies. The patient group displayed a significantly reduced number of glial cells, compared with controls, in both the submucosal and the myenteric plexus. Only 1 of the 3 populations of interstitial cells of Cajal (that associated with the deep muscular plexus) was decreased in patients. No differences were found between patients and controls concerning ganglia neurons, fibroblast-like cells, enteric neurons, apoptotic phenomena, and smooth muscle. Patients with slow-transit constipation display neuropathological abnormalities of the terminal ileum to a lesser extent than those we previously found in the colon, which might explain the abnormal motor aspects sometimes found in these patients.

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.

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.

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.

Further characterisation of particulate neuronal nitric oxide synthase in rat small intestine

Neuronal NO-synthase (nNOS) was investigated in rat longitudinal muscle/myenteric plexus (LM/MP) tissue at the cellular and subcellular level. Using preparations and double immune staining and light and electron microscopy, we concluded that, in these preparations, nNOS is only present in neuronal cells. However, in spite of numerous attempts to morphologically identify the NOS-containing subcellular structure, no firm conclusions were possible. Consequently, the problem was approached by biochemical methods including gradient centrifugation followed by analysis of the fractions. Using a protocol involving gentle homogenisation of the tissue, we found that about 10% of the nNOS immune reactivity was particle-bound confirming previous results (Biochem. Pharmacol. 60 (2000) 145). However, applying a different protocol including strong homogenisation, we now demonstrated that about 50% of the immune reactive nNOS was sedimentable. The results suggested that particulate nNOS is associated with one single subcellular structure, which is different from the plasma membrane, rough and smooth endoplasmic reticulum, mitochondria and lysosomes. The equilibrium sedimentation characteristics of the nNOS containing particles corresponded partly to those containing vasoactive intestinal polypeptide (VIP) or synaptobrevin. Application of non-equilibrium centrifugation conditions, however, demonstrated that almost no co-localisation occurred. We conclude that, in the LM/MP tissue, nNOS is about 50% particle-bound in a subcellular structure, which is different from the VIP-containing particle and from synaptobrevin-containing exocytotic particles.

Coupling and innervation patterns of interstitial cells of Cajal in the deep muscular plexus of the guinea-pig

Interstitial cells in the deep muscular plexus (ICC-DMP) are thought to be essential for neurotransmission in the circular muscle. There is evidence for gap junctions within the ICC-DMP network and between ICC-DMP and muscle cells; however, there is no evidence for functional coupling via these gap junctions. In addition, the innervation of individual ICC-DMP has not been studied. We investigated these questions by injecting the dye Lucifer yellow into ICC-DMP of guinea-pig ileum. Nerves were labelled immunohistochemically for protein gene product 9.5. Cells were imaged by confocal microscopy. Most (79%) of the dye-injected ICC-DMP were coupled to one to five other ICC-DMP, and 86% of them were coupled to one to five circular muscle cells. Octanol effectively blocked all coupling. Incubation in pH 6.8-7.0 reduced ICC-ICC coupling to 49% and ICC-muscle coupling to 32%. In contrast, pH 7.8-7.9 increased ICC-ICC and ICC-muscle coupling to 100%. Most ICC somata (95%) and processes (60%) were in close proximity with both nerve fibres and smooth muscle cells. These results provide direct evidence for functional coupling within the ICC-DMP network, and between this network and cells of the outer circular muscle layer and showed that coupling can be affected by pH.

Cholinergic and nitrergic innervation of ICC-DMP and ICC-IM in the human small intestine

With functional evidence emerging that interstitial cells of Cajal (ICC) play a role in smooth muscle innervation, detailed knowledge is needed about the structural aspects of enteric innervation of the human gut. Conventional electronmicroscopy (EM), immunohistochemistry and immuno-EM were performed on the musculature of the distal human ileum focusing on ICC associated with the deep muscular plexus (ICC-DMP) and intramuscular ICC (ICC-IM). ICC-DMP could be identified by EM but not by c-Kit immunohistochemistry. Immuno-EM revealed that ICC-DMP were innervated by both cholinergic and nitrergic nerves, and were the only cells to possess specialized synapse-like junctions with nerve varicosities and gap junction contacts with smooth muscle cells. c-Kit positive ICC near the deep muscular plexus were not ICC-DMP, but ICC-IM located in septa. ICC-IM were innervated by both cholinergic and nitrergic nerves but without specialized contacts. Varicosities of both nerve types were also found scattered throughout the musculature without specialized contact with any ICC. No ICC showed immunoreactivity for neuronal nitric oxide synthase. As ICC-DMP form synapse-like junctions with cholinergic and nitrergic nerves and gap junction contacts with muscle cells, it is hypothesized that ICC-DMP hold a specialized function related to innervation of smooth muscle of the human intestine.

Interstitial Cells in the Musculature of the Gastrointestinal Tract: Cajal and Beyond

Expression of the receptor tyrosine kinase KIT on cells referred to as interstitial cells of Cajal (ICC) has been instrumental during the past decade in the tremendous interest in cells in the interstitium of the smooth muscle layers of the digestive tract. ICC generate the pacemaker component (electrical slow waves of depolarization) of the smooth musculature and are involved in neurotransmission. By integration of ICC functions, substantial progress has been made in our understanding of the neuromuscular control of gastrointestinal motility, opening novel therapeutic perspectives. In this article, the ultrastructure and light microscopic morphology, as well as the functions and the development of ICC and of neighboring fibroblast-like cells (FLC), are critically reviewed. Directions for future research are considered and a unifying concept of mesenchymal cells, either KIT positive (the "ICC") or KIT negative "non-Cajal" (including the FLC and possibly also other cell types) cell types in the interstitium of the smooth musculature of the gastrointestinal tract, is proposed. Furthermore, evidence is accumulating to suggest that, as postulated by Santiago Ramon y Cajal, the concept of interstitial cells is not likely to be restricted to the gastrointestinal musculature.

Myenteric neurons and interstitial cells of Cajal of mouse colon express several nitric oxide synthase isoforms

Information on equipment and subcellular distribution of nitric oxide synthase (NOS) isoforms in myenteric neurons and pacemaker cells (ICC) might help to identify nitric oxide (NO) pathway(s) acting on gastrointestinal motility. In sections of mouse colon labelled with neuronal (n)NOS, endothelial (e)NOS and inducible (i)NOS antibodies, all myenteric neurons co-expressed eNOS and iNOS and a subpopulation of them co-expressed nNOS. ICC co-expressed nNOS and eNOS. In the neurons, nNOS-labeling was intracytoplasmatic, in the ICC at cell periphery. In both cell types, eNOS-labeling was on intracytoplasmatic granules, likely mitochondria. In conclusion, myenteric neurons and ICC co-express several NOS isoforms with specific subcellular distribution. Different nNOS splice variants are presumably present: intracytoplasmatic nNOSbeta and nNOSalpha producing neurogenic NO, plasma membrane-bound nNOSalpha producing ICCgenic NO. eNOS might be implicated in mitochondrial respiration and, in ICC, also in pacemaker activity. Neurons express iNOS also in basal condition.

Effect of L-NAME on decreased ileal muscle contractility induced by peritonitis in rats

BACKGROUND/PURPOSE

It is now well established that intestinal inflammation is associated with disturbed contractility. The aim of this study was to determine the effects of peritonitis on longitudinal ileum smooth muscle responses to KCl, carbachol and substance P (SP) and to examine the role of nitric oxide (NO) and N(omega)-nitro-L-arginine methylester (L-NAME) on ileal contractility in this peritonitis model.

METHODS

Peritonitis was induced by cecal ligation and puncture (CLP) in 20 rats. While 10 of these received 1 mL distilled water as placebo, the other 10 received 5 mg/kg (subcutaneously) L-NAME before the operation. Another group of 10 rats underwent a sham operation. Twenty-four hours after the operation, the rats were killed, and their ileum was excised. Ileum segments were placed in longitudinal direction in a 10-mL organ bath; concentration-response relationship for KCl, carbachol, and SP were obtained by adding the reagent cumulatively to the bath.

RESULTS

The KCl-, carbachol-, and SP-induced contractions were decreased markedly, with no change in the pD(2) values in the peritonitis group compared with controls. Peritonitis-induced changes in the contractile responses were restored significantly by in vivo L-NAME pretreatment.

CONCLUSIONS

The model of CLP-induced peritonitis in rats showed that KCl-induced nonreceptor-mediated, carbachol- and SP-induced receptor-mediated contractions are significantly decreased by inflammation in the longitudinal ileum muscle. Increased synthesis of NO may be responsible for these decreases in contractile responses because they were restored significantly by in vivo L-NAME injection. Inhibition of NOS with L-NAME injection may afford a new therapeutic approach to the treatment of gastrointestinal stasis in septic patients.

Gastrointestinal stromal tumors and KIT-positive mesenchymal cells in the omentum

Gastrointestinal stromal tumor (GIST) is currently considered to be derived from the interstitial cells of Cajal (ICC). To test the hypothesis that omental mesenchymal tumor is also a type of GIST, we evaluated the expression of specific molecules in GIST, and c-kit gene mutation in omental mesenchymal tumors, and we identified a possible counterpart of ICC in the omentum. Immunohistochemically, all of the omental mesenchymal tumors (n = 5) were positive for both KIT and CD34, and three of the five tumors were also positive for an embryonic form of smooth-muscle myosin heavy chain (SMemb). Polymerase chain reaction-single-strand conformational polymorphism analysis (PCR-SSCP) and direct sequencing revealed mutations in c-kit gene exon 11 in all five tumors. As for the ICC counterparts in the omentum, there were some KIT-positive mesenchymal cells resembling ICC at the surface of the omentum. Double fluorescence immunostaining, using anti-KIT polyclonal antibodies and monoclonal antibodies against other molecules, demonstrated that KIT-, CD34- and SMemb-positive cells were present just beneath the mesothelial cells of the omentum. These results show that omental mesenchymal tumor corresponds to GIST of the omentum, and that KIT-positive bipolar mesenchymal cells may be a counterpart of ICC in the gastrointestinal tract. Identification of a new type of KIT-positive mesenchymal cell in the omentum may lead to the discovery of a new physiological role for this organ.

Haem oxygenase in enteric nervous system of human stomach and jejunum and co-localization with nitric oxide synthase

Recent evidence suggests that carbon monoxide (CO) may be a neurotransmitter, similar to nitric oxide (NO) in the enteric nervous system. The distribution of haem oxygenase (HO), the biosynthetic enzyme for CO, has been determined in the enteric nervous system of animals, but little is known about the distribution of HO in human gastrointestinal tract. The present study investigated the expression of HO and its colocalization with NO synthase (NOS), the biosynthetic enzyme for NO, in human antrum and jejunum. HO isoforms were identified using immunohistochemistry and NOS was identified by immunohistochemistry or NADPH-d histochemistry. HO-2 immunoreactive (IR) cell bodies in enteric ganglia and nerve fibres in longitudinal and circular muscle were found in both antrum and jejunum. Co-localization of HO-2 and NOS was about 40% in HO-2 containing cell bodies of myenteric ganglia and only 10% or less in cell bodies of submucous ganglia. HO-1 immunoreactivity was not detected in antrum or jejunum. The results suggest that CO is produced in human enteric ganglion neurones and indicate a possible role of CO as a neurotransmitter and possible interaction between HO and NOS pathways in inhibitory neurotransmission in the human gastrointestinal tract.

Quantitative analysis of intestinal motor patterns: spatiotemporal organization of nonneural pacemaker sites in the rat ileum

BACKGROUND & AIMS

Intestinal contractions are triggered by electric activity of pacemaker cells within the smooth muscle. However, the precise spatial organization of the pacemaker system is unknown. We directly assessed the spatiotemporal organization of pacemakers by video image analysis combined with manometry and electromyography.

METHODS

Isolated segments of rat ileum were perfused arterially with oxygenated fluorocarbon solution and luminally with saline. Luminal end pressures, extracellular electric activity, and images of the intestine were recorded simultaneously. Tetrodotoxin, N(G)-nitro-L-arginine methyl ester (L-NAME), L-arginine, and eserine were administered arterially.

RESULTS

Myogenic contractions originated in discrete areas (dominant pacemakers) and propagated faster in aboral than in oral direction. Dominant pacemakers were distributed along the intestine at regular intervals. The preparations were mostly driven by 1 pacemaker at the time, but 2 or 3 pacemakers with different frequencies could be active simultaneously. Tetrodotoxin decreased aboral propagation velocity and revealed multiple regularly spaced pacemaker areas. Eserine increased, whereas L-arginine decreased, their frequency. After L-NAME, pacemaker activity increased and isolated pacemakers with higher frequency appeared.

CONCLUSIONS

Nonneural pacemakers in rat ileum are functionally organized not as a continuous system but show a segmental arrangement, spatially and temporally modulated by neural activity.

Effect of exogenous ATP on canine jejunal smooth muscle

Intracellular recordings were made from the circular smooth muscle cells of the canine jejunum to study the effect of exogenous ATP and to compare the ATP response to the nonadrenergic, noncholinergic (NANC) inhibitory junction potential (IJP) evoked by electrical field stimulation (EFS). Under NANC conditions, exogenous ATP evoked a transient hyperpolarization (6.5 +/- 0.6 mV) and EFS evoked a NANC IJP (17 +/- 0.4 mV). Omega-conotoxin GVIA (100 nM) and a low-Ca(2+), high-Mg(2+) solution abolished the NANC IJP but had no effect on the ATP-evoked hyperpolarization. The ATP-evoked hyperpolarization and the NANC IJP were abolished by apamin (1 microM) and N(G)-nitro-L-arginine (100 microM). Oxyhemoglobin (5 microM) partially (38.8 +/- 5.5%) reduced the amplitude of the NANC IJP but had no effect on the ATP-evoked hyperpolarization. Neither the NANC IJP nor the ATP-evoked hyperpolarization was affected by P2 receptor antagonists or agonists, including suramin, reactive blue 2, 1-(N, O-bis-[5-isoquinolinesulfonyl]-N-methyl-L-tyrosyl)-4-phenylpiperazine , pyridoxal phosphate-6-azophenyl-2',4'-disulfonic acid, alpha, beta-methylene ATP, 2-methylthioadenosine 5'-triphosphate tetrasodium salt, and adenosine 5'-O-2-thiodiphosphate. The data suggest that ATP evoked an apamin-sensitive hyperpolarization in circular smooth muscle cells of the canine jejunum via local production of NO in a postsynaptic target cell.

Receptors in interstitial cells of Cajal: identification and possible physiological roles

Interstitial cells of Cajal (ICCs) are specialized cells of the gastrointestinal tract forming distinct populations depending on their location in the gut wall. Morphological observations and functional data have led to the hypothesis of two functions for the ICCs: (1) as pacemakers of the rhythmic activity; (2) as intermediaries in neural inputs to the muscle. The identification of specific receptors on the ICCs has represented an important step in the knowledge of these cells. Immunohistochemical labeling of these receptors provided information on both ICC morphology and contacts (particularly those with nerve endings) and on the functions of these cells. All ICC possess the Kit receptor, which represents the best tool to identify these cells under the light microscope. It has been demonstrated that this receptor is essential for ICC differentiation, and, by using mutant mice lacking the Kit-related gene, it has been possible to discriminate among all the ICC those with a primary role as pacemakers. The ileal ICC, in particular those at the deep muscular plexus, express the tachykinin receptor NK1 and a subtype of somatostatin receptors and contain nitric oxide synthase. All these data support a primary role of these ICC in neural transmission.

Gap junctions in intestinal smooth muscle and interstitial cells of Cajal

This manuscript reviews gap junctions' roles in control of intestinal motility. Gap junctions (GJs) of small intestine (SmIn) are found between circular muscle (CM) cells, between interstitial cells of Cajal (ICC) of deep muscular plexus (DMP) and between them and adjacent outer circular muscle (OCM). GJs between longitudinal muscle (LM) cells or between cells of inner circular muscle (ICM) have not been reported. Occasional GJs have been reported between ICC of the myenteric plexus (MyP) and rarely between these ICC and adjacent LM or CM cells, or between ICC within CM and smooth muscle cells. In the colon (Co) of several species a special network of ICC lines the inner border of CM, the submuscular plexus (SP). GJs are found between ICCs and between them and CM cells. The ICC of MyP of Co are associated with LM and CM; occasional GJs exist between ICC and each muscle layer. Small GJs are missed by electron microscopy or light microscopic Immunocytochemistry. Therefore, GJ coupling may exist without demonstrated GJs. The consequences for the pacemaking functions of ICC networks of varied densities of GJ between ICC and between ICC of MyP or DMP or of SP and CM are considered. Connexins (Cxs) that compose intestinal GJs may affect coupling, but are incompletely known. Understanding of the role of GJs in coordinating intestinal motility requires knowing: (1) what passes through gap junctions to couple ICC to smooth muscle cells; (2) what Cx with what conductances and what modulatory controls connect ICC and smooth muscle cells; (3) whether smooth muscles can generate slow waves independent of ICC networks; and (4) what happens to motility, slow waves, and IJPs when GJs are selectively uncoupled.

Heme oxygenase, carbon monoxide, and interstitial cells of Cajal

Interstitial cells of Cajal play a central role in the control of gastrointestinal motility. The mechanisms of communication between interstitial cells of Cajal and smooth muscle cells are to a large extent unknown. This article reviews the potential role of carbon monoxide as a messenger molecule between interstitial cells of Cajal and gastrointestinal smooth muscle cells. The machinery required for the formation of carbon monoxide is present in interstitial cells of Cajal and gastrointestinal smooth muscle cells express a target site of action for carbon monoxide, a potassium channel. Carbon monoxide may, therefore, be produced in interstitial cells of Cajal and function as a messenger molecule between interstitial cells of Cajal and gastrointestinal smooth muscle cells.

Guide to the identification of interstitial cells of Cajal

The interstitial cell of Cajal, abbreviated ICC, is a specific cell type with a characteristic distribution in the smooth muscle wall throughout the alimentary tract in humans and laboratory mammals. The number of publications relating to ICC is rapidly increasing and demonstrate a rich variation in the structure and organization of these cells. This variation is species-, region-, and location-dependent. We have chosen to define a "reference ICC," basically the ICC in the murine small intestine, as a platform for discussion of variability. The growing field of ICC markers for light and electron microscopy is reviewed. Although there is a rapidly increasing number of approaches applicable to bright field and fluorescence microscopy, the location of markers by electron microscopy still suffers from inadequate preservation of ultrastructural detail. Finally, we summarize evidence related to ICC ultrastructure under conditions differing from those of the normal, adult individual (during differentiation, in pathological conditions, transplants, mutants, and in cell culture).

Substance P immunoreactive nerves and interstitial cells of Cajal in the rat and guinea-pig ileum. A histochemical and quantitative study

The substance P (SP)-containing nerves at the deep (DMP) and myenteric (MP) plexuses and the related interstitial cells of Cajal (ICC-DMP and ICC-MP) were immunohistochemically studied in rat and guinea-pig ileum. All the ICC expressed SP-preferred receptor NK1r: the ICC-DMP showed an intense and the ICC-MP a faint NK1r-immunoreactivity(IR). c-kit-labeling confirmed that they were ICC. The SP-IR nerves at the DMP were significantly more numerous in the guinea-pig than in the rat, and more numerous than those at the MP in both animal species. All the ICC-DMP in the guinea-pig and half of them in the rat were close to SP-IR nerves. The ICC-MP were rarely near to SP-IR nerves in either species. The SP-innervation shows interspecies differences at the DMP that imply a different tachykinergic control of the local ICC.

Ileal nitric oxide formation is altered in the young rat in response to endotoxin: effects of exposure to alcohol in utero

This study was designed to test the hypothesis that the activity and expression of iNOS in the ileum will be altered in young rats exposed to alcohol in utero (FAE). The subjects, 26-29-day-old rats, were progeny of dams fed an alcohol diet during gestation and their pair-fed/control cohorts. We determined the effects of endotoxin administration on ileal iNOS enzymatic activity and on ileal iNOS immunoreactivity. The basal levels of the measured variables were not significantly different between the groups. In response to LPS, however, FAE animals responded with a greater increase in ileal iNOS activity and immunoreactivity. The findings indicate that ileal iNOS is augmented in response to immune signals, which may partly account for the altered gut functions associated with FAE.

Immunohistochemical distribution of c-Kit-positive cells and nitric oxide synthase-positive nerves in the guinea-pig small intestine

Anatomical relationships between c-Kit-positive cells and nitric oxide synthase-positive nerves in the small intestine were examined by double-labeling immunohistochemistry. Cryosections and whole mount preparations of the guinea-pig small intestine were double-immunolabeled using anti-c-Kit and neuronal nitric oxide synthase antibodies, and were observed using confocal laser scanning microscopy. The c-Kit-like immunoreactivity constituted dense reticular networks in the deep muscular plexus and myenteric plexus of the intestinal wall. The nitric oxide synthase-like immunoreactivity occurred in the circular muscle layer, most densely at the deep muscular plexus, as well as within the ganglion strands or connecting strands of the myenteric plexus. Close association between c-Kit-like immunoreactivity and nitric oxide synthase-like immunoreactivity was evident in the deep muscular plexus. Specimens immunolabeled with the anti-nitric oxide synthase antibody were further examined under transmission electron microscopy. Axon profiles with nitric oxide synthase-like immunoreactivity lay closely adjacent to the interstitial cells in the deep muscular plexus as well as to smooth muscle cells of the circular muscle layer, whereas there was a considerable distance (> 500 nm) between interstitial cells and axon profiles with nitric oxide synthase-like immunoreactivity in the myenteric plexus. These results suggest that the interstitial cells in the deep muscular plexus serve as mediators of the nitrergic neurotransmission to the musculature in the small intestine, playing a role in the regulation of intestinal movement.

Chemosensory Perception in the Gut

The ability of the gut mucosa to sense the chemical composition of chyme is important for gastrointestinal functions. The demonstration of gustducin and transducin, two alpha-subunits of GTP-binding proteins involved in gustatory signal transduction, in gastrointestinal epithelial cells provides first clues to the molecular basis of enteric chemosensitivity. Nitric oxide may play a role as a secondary messenger.

Searching for intrinsic properties and functions of interstitial cells of Cajal

Evidence is mounting that interstitial cells of Cajal may function as pacemaker cells and have a role in NO-mediated neurotransmission. Several colonic motor disorders may be associated with abnormal ICC function.

Characterization and splice variants of neuronal nitric oxide synthase in rat small intestine

The aim of this study was to characterize neuronal nitric oxide synthase (nNOS) activity and 5'-end splice variants in rat small intestine. nNOS was predominantly expressed in the longitudinal muscle layer, with attached myenteric plexus (LM-MP). The biochemical properties of NOS activity in enriched nerve terminals resemble those of nNOS isolated from the brain. Western blot analysis of purified NOS protein with an nNOS antibody showed a single band in the particulate fraction and three bands in the soluble fraction. Rapid amplification of 5' cDNA ends-PCR revealed the presence of three different 5'-end splice variants of nNOS. Two variants encode for nNOSalpha, which has a specific domain for membrane association. The third variant encodes for nNOSbeta, which lacks the domain for membrane association and should therefore be soluble. nNOS is predominantly expressed in LM-MP and can be enriched in enteric nerve terminals. We present the first evidence that three 5'-end splice variants of nNOS encoding two different proteins are expressed in rat small intestine. These two nNOS enzymes exhibit different subcellular locations and might be implicated in different biological functions.

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

BACKGROUND & AIMS

Previous studies have suggested that a specific class of interstitial cells of Cajal (ICC) act as mediators in nitrergic inhibitory neurotransmission. The aim of this investigation was to examine the role of intramuscular ICC (IC-IM) in neurotransmission in the murine lower esophageal (LES) and pyloric sphincters (PS).

METHODS

Immunohistochemistry and electrophysiology were used to study the distribution and role of IC-IM.

RESULTS

The LES and PS contain spindle-shaped IC-IM, which form close relationships with nitric oxide synthase-containing nerve fibers. The PS contains ICC within the myenteric plexus and c-Kit immunopositive cells along the submucosal surface of the circular muscle. IC-IM were absent in the LES and PS of c-kit (W/Wv) mutant mice. Using these mutants, we tested whether IC-IM mediate neural inputs in the LES and PS. Although the distribution of inhibitory nerves was normal in W/Wv animals, NO-dependent inhibitory neurotransmission was reduced. Hyperpolarizations to sodium nitroprusside were also attenuated in W/Wv animals.

CONCLUSIONS

The data suggest that IC-IM play an important role in NO-dependent neurotransmission in the LES and PS. IC-IM may be the effectors that transduce NO signals into hyperpolarizing responses. Loss of IC-IM may interfere with relaxations and normal motility in these sphincters.