Heme oxygenase, carbon monoxide, and interstitial cells of Cajal

Carbon monoxide, hydrogen sulfide, and nitric oxide as signaling molecules in the gastrointestinal tract

Carbon monoxide (CO) and hydrogen sulfide (H2S) used to be thought of simply as lethal and (for H2S) smelly gaseous molecules; now they are known to have important signaling functions in the gastrointestinal tract. CO and H2S, which are produced in the gastrointestinal tract by different enzymes, regulate smooth muscle membrane potential and tone, transmit signals from enteric nerves, and can regulate the immune system. The pathways that produce nitric oxide, H2S, and CO interact; each can inhibit and potentiate the level and activity of the other. However, there are significant differences between these molecules, such as in half-lives; CO is more stable and therefore able to have effects distal to the site of production, whereas nitric oxide and H2S are short lived and act only close to sites of production. We review their signaling functions in the luminal gastrointestinal tract and discuss how their pathways interact. We also describe other physiological functions of CO and H2S and how they might be used as therapeutic agents.

Altered expression of Ano1 variants in human diabetic gastroparesis

Diabetes affects many organs including the stomach. Altered number and function of interstitial cells of Cajal (ICC), the gastrointestinal pacemaker cells, underlie a number of gastrointestinal motility disorders, including diabetic gastroparesis. In the muscle layers, ICC selectively express Ano1, thought to underlie classical Ca(2+)-activated Cl(-) currents. Mice homozygous for Ano1 knock-out exhibit abnormal ICC function and motility. Several transcripts for Ano1 are generated by alternative splicing of four exons. Here, we report expression levels of transcripts encoded by alternative splicing of Ano1 gene in gastric muscles of patients with diabetic gastroparesis and nondiabetic control tissues. Expression of mRNA from two alternatively transcribed exons are significantly different between patients and controls. Furthermore, patients with diabetic gastroparesis express mRNA for a previously unknown variant of Ano1. The 5' end of this novel variant lacks exons 1 and 2 and part of exon 3. Expression of this variant in HEK cells produces a decreased density of Ca(2+)-activated Cl(-) currents that exhibit slower kinetics compared with the full-length Ano1. These results identify important changes in expression and splicing of Ano1 in patients with diabetic gastroparesis that alter the electrophysiological properties of the channel. Changes in Ano1 expression in ICC may directly contribute to diabetic gastroparesis.

Effects of prostaglandin F2α on small intestinal interstitial cells of Cajal

AIM: To explore the role of prostaglandin F_2α (PGF_2α)) on pacemaker activity in interstitial cells of Cajal (ICC) from mouse small intestine.

METHODS: In this study, effects of PGF_2α in the cultured ICC cells were investigated with patch clamp technology combined with Ca²⁺ image analysis.

RESULTS: Externally applied PGF_2α (10 μmol/L) produced membrane depolarization in current-clamp mode and increased tonic inward pacemaker currents in voltage-clamp mode. The application of flufenamic acid (a non-selective cation channel inhibitor) or niflumic acid (a Cl^- channel inhibitor) abolished the generation of pacemaker currents but only flufenamic acid inhibited the PGF_2α-induced tonic inward currents. In addition, the tonic inward currents induced by PGF_2α were not inhibited by intracellular application of 5’-[-thio]diphosphate trilithium salt. Pretreatment with Ca²⁺ free solution, U-73122, an active phospholipase C inhibitor, and thapsigargin, a Ca²⁺-ATPase inhibitor in endoplasmic reticulum, abolished the generation of pacemaker currents and suppressed the PGF_2α-induced tonic inward currents. However, chelerythrine or calphostin C, protein kinase C inhibitors, did not block the PGF_2α-induced effects on pacemaker currents. When recording intracellular Ca²⁺ ([Ca²⁺]_i) concentration using fluo-3/AM, PGF_2α broadly increased the spontaneous [Ca²⁺]_i oscillations.

CONCLUSION: These results suggest that PGF_2α can modulate pacemaker activity of ICC by acting non-selective action channels through phospholipase C-dependent pathway via [Ca²⁺]i regulation

New insights into the pathogenesis of infantile pyloric stenosis

Infantile hypertrophic pyloric stenosis (IHPS) is the most common surgical cause of vomiting in infants. Despite numerous hypotheses, the aetiopathogenesis of IHPS is not fully understood. Genetic, extrinsic and hormonal factors have been implicated in the pathogenesis of the disease. Furthermore, abnormalities of various components of the pyloric muscle such as smooth muscle cells, growth factors, extracellular matrix elements, nerve and ganglion cells, synapses, nerve supporting cells, neurotransmitters and interstitial cells of Cajal have been reported. Recently, genetic studies have identified susceptibility loci for IHPS and molecular studies have concluded that smooth muscle cells are not properly innervated in IHPS.

Interstitial cells of Cajal in health and disease

The gastrointestinal tract serves the physiological function of digesting and absorbing nutrients from food and physically mixing and propelling these contents in an oral to anal direction. These functions require the coordinated interaction of several cell types, including enteric nerves, immune cells and smooth muscle. Interstitial cells of Cajal (ICC) are now recognized as another cell type that are required for the normal functioning of the gastrointestinal tract. Abnormalities in ICC numbers and networks are associated with several gastrointestinal motility disorders. This review will describe what is known about the function and role of ICC both in health and in a variety of motility disorders with a focus on unresolved issues pertaining to their role in the control of gastrointestinal motility.

Increase in stretch-induced rhythmic motor activity in the diabetic rat colon is associated with loss of ICC of the submuscular plexus

Diabetes affects many aspects of gastrointestinal motility, in part due to changes in interstitial cells of Cajal (ICC). The effect of diabetes on the colon, however, is not well characterized, and the aim of the present study was to investigate possible relationships between altered colonic motility as a consequence of streptozotocin-induced diabetes and injury to ICC. Physiological, immunohistochemical, and ultrastructural techniques were employed. The motor pattern of the rat colon was dominated by rhythmic high-amplitude, low-frequency contractions that were primarily myogenic in origin. These rhythmic contractions were induced by stretch associated with increased tension; the amplitude of the superimposed rhythmic contractions increased with increasing applied tension. In diabetic rats, the stretch-induced rhythmic contractile activity remained robust and of similar frequency but was significantly higher in amplitude compared with that in control rats. At 700 mg of applied tension, the force of contraction in circular colonic muscle strips of the diabetic rats was 370% of control values. This robust presence of low-frequency contractions is consistent with the unaffected pacemaker, the ICC associated with Auerbach's plexus, and the increased amplitude correlates with loss of and injury to ICC of the submuscular plexus and intramuscular ICC. Loss of inhibitory nitrergic nerves does not appear to be a factor based on unaltered nNOS immunoreactivity.

Interstitial cells of Cajal in the normal gut and in intestinal motility disorders of childhood

Interstitial cells of Cajal (ICCs) are pacemaker cells which are densely distributed throughout the whole gastrointestinal tract. ICCs have important functions in neurotransmission, generation of slow waves and regulation of mechanical activities in the gastrointestinal tract, especially for the coordinated gastrointestinal peristalsis. Therefore, a loss of ICCs could result in gastrointestinal motor dysfunction. In recent years c-kit labeling has been widely used to study pathological changes of ICCs in gastrointestinal motility disorders. Paediatric gastrointestinal motility disorders such as hypertrophic pyloric stenosis, Hirschsprung's disease, total colonic aganglionosis, hypoganglionosis, intestinal neuronal dysplasia, internal anal sphincter achalasia, megacystis microcolon intestinal hypoperistalsis syndrome have been reported to be associated with loss or deficiency of ICCs networks. This review describes the distribution of ICCs in the normal gastrointestinal tract and its altered distribution in intestinal motility disorders of childhood.

Heme in intestinal epithelial cell turnover, differentiation, detoxification, inflammation, carcinogenesis, absorption and motility

The gastrointestinal tract is lined by a simple epithelium that undergoes constant renewal involving cell division, differentiation and cell death. In addition, the epithelial lining separates the hostile processes of digestion and absorption that occur in the intestinal lumen from the aseptic environment of the internal milieu by defensive mechanisms that protect the epithelium from being breached. Central to these defensive processes is the synthesis of heme and its catabolism by heme oxygenase (HO). Dietary heme is also an important source of iron for the body which is taken up intact by the enterocyte. This review describes the recent literature on the diverse properties of heme/HO in the intestine tract. The roles of heme/HO in the regulation of the cell cycle/apoptosis, detoxification of xenobiotics, oxidative stress, inflammation, development of colon cancer, heme-iron absorption and intestinal motility are specifically examined.

Downregulation of two novel genes in Sl/Sld and W(LacZ)/Wv mouse jejunum

Interstitial cells of Cajal (ICC) are the so-called pacemaker cells of the gut. W(LacZ)/Wv and Sl/Sld mice lack ICC surrounding the myenteric plexus (MP) in the jejunum. We compared the gene expression profile of wild type (WT) and W(LacZ)/Wv and Sl/Sld mice using suppression subtractive hybridization (SSH), generating a cDNA library of 1303 clones from which 48 unique sequences were differentially expressed with Southern blot. Among them, we identified heme oxygenase2, TROY, and phospholamban in ICC using immunohistochemistry. Using RT-qPCR, c-Kit and two new transcripts Dithp and prenylcysteine oxidase1 were significantly lower expressed in Sl/Sld and W(LacZ)/Wv versus WT. Prenylcysteine oxidase1 appeared cytotoxic for COS-7 cells and was highly expressed in liver while Dithp was mainly expressed in small intestine. The combination of SSH, Southern blot, RT-qPCR, and immunohistochemistry turned out to be a useful approach to identify rarely expressed genes and genes with small differences in expression.

Volume-activated chloride currents in interstitial cells of Cajal

Interstitial cells of Cajal (ICC) undergo marked morphological changes on contraction of the musculature, making it essential to understand properties of mechanosensitive ion channels. The whole cell patch-clamp technique was used to identify and to characterize volume-activated Cl- currents in ICC cultured through the explant technique. Hypotonic solutions (approximately 210 mosM) activated an outwardly rectifying current, which reversed near the equilibrium potential for Cl-. Time-dependent inactivation occurred only at pulse potentials of +80 mV, with a time constant of 478 +/- 182 ms. The degree of outward rectification was calculated using a rectification index, the ratio between the slope conductances of +65 and -55 mV, which was 13.9 +/- 1.5 at 76 mM initial extracellular Cl- concentration. The sequence of relative anion permeability of the outwardly rectifying Cl- channel was I- > Cl- > aspartate-. The chloride channel blockers, DIDS and 5-nitro-2-(3-phenlypropl-amino)benzoic acid, caused a voltage-dependent block of the outwardly rectifying Cl- current, inhibition occurring primarily at depolarized potentials. On exposure to hypotonic solution, the slope conductance significantly increased at the resting membrane potential (-70 mV) from 1.2 +/- 0.2 to 2.0 +/- 0.4 nS and at the slow-wave plateau potential (-35 mV) from 2.1 +/- 0.3 to 5.0 +/- 1.0 nS. The current was constitutively active in ICC and contributed to the resting membrane potential and excitability at the slow-wave plateau. In conclusion, swelling or volume change will depolarize ICC through activation of outwardly rectifying chloride channels, thereby increasing cell excitability.

Interstitial cells in the vasculature

Interstitial cells of Cajal are believed to play an important role in gastrointestinal tissues by generating and propagating electrical slow waves to gastrointestinal muscles and/or mediating signals from the enteric nervous system. Recently cells with similar morphological characteristics have been found in the wall of blood vessels such as rabbit portal vein and guinea pig mesenteric artery. These non-contractile cells are characterised by the presence of numerous processes and were easily detected in the wall of the rabbit portal vein by staining with methylene blue or by antibodies to the marker of Interstitial Cells of Cajal c-kit. These vascular cells have been termed "interstitial cells" by analogy with interstitial cells found in the gastrointestinal tract. Freshly dispersed interstitial cells from rabbit portal vein and guinea pig mesenteric artery displayed various Ca2+-release events from endo/sarcoplasmic reticulum including fast localised Ca2+ transients (Ca2+ sparks) and longer and slower Ca2+ events. Single interstitial cells from the rabbit portal vein, which is a spontaneously active vessel, also demonstrated rhythmical Ca2+ oscillations associated with membrane depolarisations, which suggests that in this vessel interstitial cells may act as pacemakers for smooth muscle cells. The function of interstitial cells from the mesenteric arteries is yet unknown. This article reviews some of the recent findings regarding interstitial cells from blood vessels obtained by our laboratory using electron microscopy, immunohistochemistry, tight-seal patch-clamp recording, and fluorescence confocal imaging techniques.

Smooth muscle cells and interstitial cells of blood vessels

A rise in intracellular ionised calcium concentration ([Ca(2+)](i)) at sites adjacent to the contractile proteins is a primary signal for contraction in all types of muscles. Recent progress in the development of imaging techniques with special accent on the fluorescence confocal microscopy and new achievements in the synthesis of organelle- and ion-specific fluorochromes provide an experimental basis for study of the relationship between the structural organisation of the living smooth muscle myocyte and the features of calcium signalling at subcellular level. Applying fluorescent confocal microscopy and tight-seal recording of transmembrane ion currents to freshly isolated vascular myocytes we have demonstrated that: (1) Ca(2+) sparks originate from clustered opening of ryanodine receptors (RyRs) and build up a cell-wide increase in [Ca(2+)](i) upon myocyte excitation; (2) spontaneous Ca(2+) sparks occurred at the highest rate at certain preferred locations, frequent discharge sites (FDS), which are associated with a prominent portion of the sarcoplasmic reticulum (SR) located close to the cell membrane; (3) Ca(2+)-dependent K(+) and Cl(-) channels sense the local changes in [Ca(2+)](i) during a calcium spark and thereby couple changes in [Ca(2+)](i) within a microdomain to changes in the membrane potential, thus affecting excitability of the cell; (4) an intercommunication between RyRs and inositol trisphosphate receptors (IP(3)Rs) is one of the important determinants of intracellular calcium dynamics that, in turn, can modulate the cell membrane potential through differential targeting of calcium dependent membrane ion channels. Furthermore, using immunohystochemical approaches in combination with confocal imaging we identified non-contractile cells closely resembling interstitial cells (ICs) of Cajal (which are considered to be pacemaker cells in the gut) in the wall of portal vein and mesenteric artery. Using electron microscopy, tight-seal recording and fluorescence confocal imaging we obtained information on the morphology of ICs and their possible coupling to smooth muscle cells (SMCs), calcium signalling in ICs and their electrophysiological properties. The functions of these cells are not yet fully understood; in portal vein they may act as pacemakers driving the spontaneous activity of the muscle; in artery they may have other a yet unsuspected functions.

The role of carbon monoxide in the gastrointestinal tract

Carbon monoxide (CO) is a biologically active product of haem metabolism that contributes to the normal physiology of the gastrointestinal tract. In this article, we review recent data showing that CO is an integral regulator of gastrointestinal motility and an important factor in the response to gastrointestinal injury. CO is generated by haem oxygenase-2 (HO-2), which is constitutively expressed in many inhibitory neurones of the vertebrate enteric nervous system. The membrane potential gradients along and across the muscle layers of the gastrointestinal tract require the generation of CO by haem oxygenase-2. The presence of CO is also necessary for normal inhibitory neurotransmission in circular smooth muscle and appears to permit nitric oxide-mediated inhibitory neurotransmission. Genetic deletion of the haem oxygenase-2 gene in mice slows gut transit. The other major CO synthetic enzyme, haem oxygenase-1 (HO-1) is induced under conditions of stress or injury. Recent studies have demonstrated that up-regulation of haem oxygenase-1 protects the gut from several types of gastrointestinal injury, suggesting that CO or induction of HO-1 may find therapeutic use in gastrointestinal diseases and injuries. Furthermore, it is anticipated that the understanding of CO-mediated signalling in the gastrointestinal tract will inform studies in other tissues that express haem oxygenases.

A new model of pacing in the mouse intestine

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

Distribution of interstitial cells of Cajal in the internal anal sphincter of patients with internal anal sphincter achalasia and Hirschsprung disease

CONTEXT

Interstitial cells of Cajal (ICCs) are pacemaker cells in the smooth muscles of the gut. The internal anal sphincter (IAS) is the most caudal part of gastrointestinal tract. It has the important function of maintaining fecal continence. It has been proposed that ICCs in the IAS mediate the inhibitory innervation of the recto-anal reflexes.

OBJECTIVE

To investigate the distribution of ICCs in the normal IAS and in the IAS of children diagnosed with internal anal sphincter achalasia (IASA) and Hirschsprung disease (HD).

METHODS

At the time of IAS myectomy, specimens of the IAS were taken from 8 patients with IASA, 4 patients with HD, and 4 normal controls. All specimens were examined using anti-c-Kit and antiperipherin antibodies; immunolocalization was detected with light microscopy. Density of the ICCs was graded by computerized image analysis.

RESULTS

There was strong peripherin immunoreactivity in the ganglia cells and nerve fibers in the normal IAS. The number of peripherin-positive nerve fibers was markedly reduced in the IAS in patients with IASA. In HD patients, there was lack of peripherin immunoreactivity in the IAS, but hypertrophic nerve trunks stained strongly. Many c-Kit-positive ICCs were present among the muscle fibers and between the muscle bundles in the normal IAS. In HD and IASA patients, ICCs were absent or markedly reduced.

CONCLUSION

Altered distribution of ICCs in the internal sphincter in IASA and HD may contribute to motility dysfunction in these patients.

Distribution of heme oxygenase-2 in nerves and interstitial cells of Cajal in the normal pylorus and in infantile hypertrophic pyloric stenosis

CONTEXT

Interstitial cells of Cajal (ICCs) are pacemaker cells, which are of fundamental importance in regulating gastrointestinal motility. Recent evidence suggests that carbon monoxide is a neurotransmitter involved in neurotransmission between ICC and smooth muscle cells. Heme oxygenase-2 (HO-2) is the major physiological mechanism for the generation of carbon monoxide in the enteric nervous system.

OBJECTIVE

To investigate the immunocolocalization of HO-2 and ICCs in the normal pylorus and in infantile hypertrophic pyloric stenosis (IHPS).

DESIGN

Specimens from 18 infants with IHPS and 8 control specimens were examined using double-immunostaining with c-Kit and HO-2 antibodies. The immunolocalization was detected with the help of confocal laser scanning microscopy.

RESULTS

Abundant HO-2 immunoreactivity was found in ICCs in the smooth muscle layer of normal pylorus. There was a decrease in the number of ICCs and lack of HO-2 immunoreactivity in ICCs in IHPS.

CONCLUSIONS

The results of the present study provide the first evidence for the presence of HO-2 in ICCs in the normal human pylorus. The lack of ICCs and HO-2 in IHPS suggests impaired intracellular communication between ICCs and smooth muscle cells, contributing to motility dysfunction in IHPS.

Identification of interstitial cells of Cajal in the rabbit portal vein

Two layers of interstitial cells (ICs) of Cajal were detected by c-kit and methylene blue staining in the media of the rabbit portal vein in subendothelial intramuscular and deeper intramuscular positions, displaced radially from each other by about 40-70 microm. Two morphologically distinct types of ICs were found among enzymatically dispersed cells from this vessel: small multipolar cells with stellate-shaped bodies not exceeding 20 microm, and spindle-shaped cells from 40 to 300 microm in length with numerous branching processes. Relaxed smooth muscle cells (SMCs) had a more constant length (90-150 microm). The cell membrane capacitance was 46.5+/-2.2 pF in SMCs, 39.7+/-2.4 pF in spindle-shaped ICs and 27.8+/-0.7 pF in multipolar ICs. Although darker under phase contrast, after loading with fluo-4 AM, single isolated ICs of both types usually had brighter fluorescence than SMCs and displayed various spontaneous calcium events, including Ca(2+) sparks and Ca(2+) waves. Ca(2+) waves were usually followed by contraction of SMCs but no change in shape of ICs. In some ICs spontaneous [Ca(2+)](i) transients (lasting about 2s) which propagated towards the end of the processes were observed. Physical contacts between the processes of ICs and the body of one or more SMCs survived the isolation procedure. Application of noradrenaline (1-10 microM), caffeine (1-10 mM) or high-K(+) solution (60mM) led to a rise of [Ca(2+)](i) in both SMCs and ICs evoking contraction of SMCs but not ICs. No differences in electrophysiological characteristics between single enzymatically isolated IC and SMC were detected; thus, the resting membrane potential estimated under current-clamp conditions was -46.5+/-2.0 mV in spindle-shaped ICs and -45.6+/-2.7 mV in SMCs. Under voltage-clamp, both ICs and SMCs revealed a well-developed voltage-gated nifedipine-sensitive L-type Ca(2+) current, a set of K(+) currents, including spontaneous transient outward currents (STOCs) but no Na(+) current. This study for the first time directly demonstrated the presence in vascular tissue of ICs. Possible roles for ICs including their involvement in spontaneous activity of the vessel were discussed.

Heme oxygenase in the rat ovary: immunohistochemical localization and possible role in steroidogenesis

The objectives of this study were to determine if heme oxygenase (HO), which catalyzes the degradation of heme and the formation of carbon monoxide (CO), is localized in the rat ovary and, if so, to determine if hemin (a substrate for HO) or chromium mesoporphyrin (CrMP, an inhibitor of HO), alter basal or gonadotropin-induced steroidogenesis. The hypothesis was that CO produced endogenously by HO suppresses steroid hormone production by the ovary similar to the action of nitric oxide. For the histological localization of HO, sections of ovaries obtained from mature Holtzman Sprague-Dawley rats were immunostained for two of the HO isoforms, HO-1 and HO-2. Theca cells and granulosa cells of follicles and luteal cells stained for HO-1, whereas the ovarian stroma showed a low intensity of staining. Theca, granulosa cells, and corpora lutea as well as the ovarian stroma exhibited HO-2 staining. HO-2 immunostaining appeared more intense for theca cells than granulosa cells. In the study of steroidogenesis, three daily injections of hemin stimulated basal- and gonadotropin-induced androstenedione and estradiol secretion from ovaries of pregnant mare serum gonadotropin-treated immature rats in vitro, but had no effect on progesterone production. A similar treatment with CrMP suppressed basal- and gonadotropin-induced secretion of progesterone and androstenedione, but had no effect on estradiol production. These data, taken together, show the existence of HO in the rat ovary and suggest a possible stimulatory role of endogenous CO in the production of ovarian steroids.

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.

Immunocolocalization of the heme oxygenase-2 and interstitial cells of Cajal in normal and aganglionic colon

PURPOSE

Interstitial cells of Cajal (ICCs) are pacemaker cells that play an important role in the control of gut motility. Carbon monoxide (CO) has been proposed as an endogenous messenger molecule between ICC and smooth muscle cells in the gastrointestinal tract (GIT). Heme oxygenase-2 (HO-2) is the main physiologic mechanism for generating CO in human cells. The aim of this study was to investigate the immunocolocalization of the HO-2 and ICCs in normal and aganglionic bowel of Hirschsprung's disease (HD).

METHODS

Full-thickness specimens were obtained from aganglionic colon during pull-through operation from 10 patients diagnosed as having HD. Normal control large bowel specimens were collected from 4 patients during bladder augmentation procedures. Double immunostaining was carried out using c-kit and HO-2 antibodies. Immunolocalization was detected by means of confocal laser scanning microscopy.

RESULTS

HO-2 immunoreactivity (IR) was found in many ICCs present around the myenteric plexus, within the longitudinal and circular muscle layers and at the innermost part of the circular muscle layer in normal colon. In the aganglionic colon there was absence of HO-2 IR in the sparsely found ICCs. In the transitional zone of HD bowel the colocalization of HO-2 IR and ICCs was much reduced compared with controls.

CONCLUSIONS

The results of this study provide the first evidence for the presence of HO-2 immunoreactivity in the ICCs in normal human colon and absence of HO-2 immunoreactivity in sparsely appearing ICCs in the bowel of HD patients. The lack of HO-2 in the ICCs in the bowel of HD patients may result in impaired intracellular communication between ICCs and SMCs causing motility dysfunction.

Induction of heme oxygenase in guinea-pig stomach: roles in contraction and in single muscle cell ionic currents

The role of heme oxygenase reaction products in modulation of stomach fundus excitability was studied. The presence of constitutive heme oxygenase 2 was verified in myenteric ganglia by immunohistochemistry. The role of inducible heme oxygenase isoenzyme was investigated after invivo treatment of animals with CoCl2 (80 mg kg-1 b.w) injected subcutaneously 24 h before they were killed. This treatment resulted in increased production of bilirubin and positive staining for the inducible isoform in stomach smooth muscle and vast induction in the liver. In both control and treated animals haemin, applied to the bath as a substrate of heme oxygenase caused significant decrease of prostaglandin F2alpha-induced tone, and ameliorated the relaxatory response of the fundic strips to electrical field stimulation. Both effects were antagonized by Sn-protoporphyrin IX, competitive heme oxygenase inhibitor, and were found to be neuronally dependent. In single freshly isolated smooth muscle cells from control animals haemin caused a concentration-dependent increase of the whole cell K+ currents, which was not affected by Sn-protoporphyrin IX, cyclic guanosine monophosphate (cGMP)-dependent protein kinase or guanylyl cyclase antagonists, but was reversed by various antioxidants and abolished by an NO scavenger. In cells from treated animals the K+ current increasing effect of haemin did not depend on the presence of antioxidants, but was abolished by protein kinase G and guanylyl cyclase inhibitors, depletors of intracellular Ca2+ pools or Sn-protoporphyrin IX. Biliverdin did not affect contraction or ionic currents. Thus, this is the first study demonstrating that heme oxygenase is an inducible enzyme in guinea-pigs, which exerts a modulatory role on gastric smooth muscle excitability via carbon monoxide production.

Immunohistochemical localization of the antioxidant enzymes biliverdin reductase and heme oxygenase-2 in human and pig gastric fundus

The intrinsic antioxidant capacities of the bile pigments biliverdin and bilirubin are increasingly recognized since both heme degradation products can exert beneficial cytoprotective effects due to their scavenging of oxygen free radicals and interaction with antioxidant vitamins. Several studies have been published on the localization of the carbon monoxide producing enzyme heme oxygenase-2 (HO-2), which concomitantly generates biliverdin; histochemical data on the distribution of biliverdin reductase (BVR), converting biliverdin to bilirubin, are still very scarce in large mammals including humans. The present study revealed by means of immunohistochemistry the presence of BVR and HO-2 in mucosal epithelial cells and in the endothelium of intramural vessels of both human and porcine gastric fundus. In addition, co-labeling with the specific neural marker protein-gene product 9.5 (PGP 9.5) demonstrated that both BVR and HO-2 were present in all intrinsic nerve cell bodies of both submucous and myenteric plexuses, while double labeling with c-Kit antibody confirmed their presence in intramuscular interstitial cells of Cajal (ICC). Our results substantiate the hypothesis that BVR, through the production of the potent antioxidant bilirubin, might be an essential component of normal physiologic gastrointestinal defense in man and pig.

Physiology and pathophysiology of the interstitial cell of Cajal: from bench to bedside. II. Gastric motility: lessons from mutant mice on slow waves and innervation

The stomach harbors a network of interstitial cells of Cajal (ICC) associated with Auerbach's plexus as well as intramuscular ICC within the muscle layers that make close apposition contact with nerve varicosities. ICC are critical for slow-wave generation, making ICC the pacemaker cells of the gut, allowing rhythmic peristaltic motor patterns in the mid- and distal stomach. ICC also play a role in neurotransmission, but its importance relative to direct muscle innervation is still under investigation. The role of ICC in many control functions of gastric motility in humans needs further examination. The pathophysiology of ICC in disease can be partially assessed by immunohistochemistry and electron microscopy on tissue samples. Electrogastrogram measurements may also play a role, but this technique needs further refinement. Communication between ICC and muscle may involve electrical coupling, metabolic coupling through gap junctions, or secretion of nitric oxide or carbon monoxide.

Interstitial cells of Cajal--their role in pacing and signal transmission in the digestive system

Interstitial cells of Cajal (ICC) are located in most parts of the digestive system. Although they were discovered over 100 years ago, their function began to be unravelled only recently. Morphological observations have led to a number of hypotheses on the possible physiological roles of ICC: (1) these cells may be the source of slow electrical waves recorded in gastrointestinal (GI) muscles; (2) they participate in the conduction of electrical currents, and (3) mediate neural signals between enteric nerves and muscles. These hypotheses were supported by experiments in which the ICC-containing layer was removed surgically, or when ICC were ablated chemically, and as a consequence the slow waves were absent. Electrophysiological experiments on isolated cells confirmed that ICC can generate rhythmic electrical activity and can also respond to messenger molecules known to be released from enteric nerves. In mice mutants deficient in ICC, or in mice treated with antibody against the protein c-Kit, slow wave activity was impaired. These results support the role of ICC as pacemaker cells. Physiological studies have shown that ICC in certain GI regions are important for signal transmission between nerves and smooth muscle. There is evidence that pathological changes in ICC may be associated with GI motility disorders. The full interpretation of the role of ICC in disease conditions will require much further study on the physiology and pharmacology of these cells.