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

Pacing the gut in motility disorders

Similar to cardiac pacing, gastrointestinal (GI) pacing is an attractive idea and may become a promising therapy, as the GI organs, like the heart, have their own natural pacemakers. Over the past 10 years, electrical stimulation of the gut has received increasing attention among researchers and clinicians. Several clinical studies have shown that gastric electrical stimulation (GES) with short pulses is able to reduce nausea and vomiting in patients with gastroparesis and that GES with long pulses is able to pace the intrinsic gastric slow waves and thus normalize gastric dysrhythmia. However, possible placebo effects cannot be ruled out, although recent animal studies have revealed various peripheral and central mechanisms involved with GES. Electrical stimulation of the small intestine, colon, or anal sphincter also has been reported for the treatment of dumping syndrome, constipation, and fecal incontinency. Similarly, there is a lack of placebo-controlled studies. In our opinion, pacing of the gut has great potential for the treatment of various GI motor disorders. However, none of the commercially available devices is designed for pacing the gut. The lack of well-suited devices and the invasive nature of gut pacing slow down the progress and clinical applications of gut pacing.

Receptor tyrosine and MAP kinase are involved in effects of H(2)O(2) on interstitial cells of Cajal in murine intestine

Hydrogen peroxide (H(2)O(2)) is involved in intestinal motility through changes of smooth muscle activity. However, there is no report as to the modulatory effects of H(2)O(2) on interstitial cells of Cajal (ICC). We investigated the H(2)O(2) effects and signal transductions to determine whether the intestinal motility can be modulated through ICC. We performed whole-cell patch clamp in cultured ICC from murine intestine and molecular analyses. H(2)O(2) hyperpolarized the membrane and inhibited pacemaker currents. These effects were inhibited by glibenclamide, an inhibitor of ATP-sensitive K+ (K(ATP)) channels. The free-radical scavenger catalase inhibited the H(2)O(2)-induced effects. MAFP and AACOCF3 (a cytosolic phospholipase A2 inhibitors) or SC-560 and NS-398 (a selective COX-1 and 2 inhibitor) or AH6809 (an EP2 receptor antagonist) inhibited the H(2)O(2)-induced effects. PD98059 (a mitogen activated/ERK-activating protein kinase inhibitor) inhibited the H(2)O(2)-induced effects, though SB-203580 (a p38 MAPK inhibitor) or a JNK inhibitor did not affect. H(2)O(2)-induced effects could not be inhibited by LY-294002 (an inhibitor of PI3-kinases), calphostin C (a protein kinase C inhibitor) or SQ-22536 (an adenylate cyclase inhibitor). Adenoviral infection analysis revealed H2O2 stimulated tyrosine kinase activity and AG 1478 (an antagonist of epidermal growth factor receptor tyrosine kinase) inhibited the H(2)O(2)-induced effects. These results suggest H(2)O(2) can modulate ICC pacemaker activity and this occur by the activation of K(ATP) channels through PGE(2) production via receptor tyrosine kinase-dependent MAP kinase activation.

ICC-MY coordinate smooth muscle electrical and mechanical activity in the murine small intestine

BACKGROUND

Animals carrying genetic mutations have provided powerful insights into the role of interstitial cells of Cajal (ICC) in motility. One classic model is the W/W(V) mouse which carries loss-of-function mutations in c-kit alleles, but retains minimal function of the tyrosine kinase. Previous studies have documented loss of slow waves and aberrant motility in the small intestine of W/W(V) mice where myenteric ICC (ICC-MY) are significantly depleted.

METHODS

Here, we used morphological and electrophysiological techniques to further assess the loss of ICC around the circumference of the small intestine and determine consequences of losing ICC-MY on electrical activity, Ca(2+) transients and contractions of the longitudinal muscle (LM).

KEY RESULTS

In wild-type mice, there was coherent propagation of Ca(2+) transients through the ICC-MY network and spread of this activity to the LM. In short segments of small intestine in vitro and in exteriorized segments, slow waves coordinated smoothly propagating Ca(2+) waves and contractions in the LM of wild-type mice. In W/W(V) mice, Ca(2+) waves were initiated at variable sites along and around intestinal segments and propagated without constraint unless they collided with other Ca(2+) waves. This activity resulted in abrupt, uncoordinated contractions.

CONCLUSIONS & INFERENCES

These results show how dominance of pacemaking by ICC-MY coordinates propagating con-tractions and regulates the spontaneous activity of smooth muscle.

Igf1r+/CD34+ immature ICC are putative adult progenitor cells, identified ultrastructurally as fibroblast-like ICC in Ws/Ws rat colon

The colon of Ws/Ws mutant rats shows impairment of pacemaker activity and altered inhibitory neurotransmission. The present study set out to find structural correlates to these findings to resolve mechanisms. In the colon of Ws/Ws rats, interstitial cells of Cajal associated with Auerbach's plexus (ICC-AP) were significantly decreased and ICC located at the submuscular plexus and intramuscular ICC were rarely observed based on immunohistochemistry and electron microscopy. Ultrastructural investigations revealed that there was no overall loss of all types of interstitial cells combined. Where loss of ICC was observed, a marked increase in fibroblast-like ICC (FL-ICC) was found at the level of AP. Immunoelectron microscopy proved FL-ICC to be c-Kit(-) but gap junction coupled to each other and to c-Kit(+) ICC; they were associated with enteric nerves and occupied space normally occupied by ICC in the wild-type rat colon, suggesting them to be immature ICC. In addition, a marked increase in immunoreactivity for insulin-like growth factor 1 receptor (Igf1r) occurred, co-localized with CD34 but not with c-Kit. A significantly higher number of Igf1r(+)/CD34(+) cells were found in Ws/Ws compared to wild-type rat colons. These CD34(+)/Igf1r(+) cells in the Ws/Ws colon occupied the same space as FL-ICC. Hence we propose that a subset of immature ICC (FL-ICC) consists of adult progenitor cells. Immunohistochemistry revealed a reduction of neurons positive for neuronal nitric oxide synthase. The functional capabilities of the immature ICC and the regenerative capabilities of the adult progenitor cells need further study. The morphological features described here show that the loss of pacemaker activity is not associated with failure to develop a network of interstitial cells around AP but a failure to develop this network into fully functional pacemaker cells. The reduction in nitrergic innervation associated with the Ws mutation may be the result of a reduction in nitrergic neurons.

Roles of interstitial cells of Cajal in regulating gastrointestinal motility: in vitro versus in vivo studies

The aim of this article is to provide a better understanding of the roles of interstitial cells of Cajal (ICC) in regulating gastrointestinal motility by reviewing in vitro and in vivo physiological motility studies. Based on the in vitro studies, ICC are proposed to have the following functions: to generate slow waves, to mediate neurotransmission between the enteric nerves and the gastrointestinal muscles and to act as mechanoreceptors. However, there is limited evidence available for these hypotheses from the in vivo motility studies. In this review, we first introduce the major subtypes of ICC and their established functions. Three Kit mutant mouse and rodent models are presented and the loss of ICC subtypes in these mutants is reviewed. The physiological motility findings from various in vitroand in vivo experiments are discussed to give a critical review on the roles of ICC in generating slow waves, regulating gastrointestinal motility, mediating neural transmission and serving as mechanoreceptors. It is concluded that the role of ICC as pacemakers may be well established, but other cells may also be involved in the generation of slow waves; the theory that ICC are mediators of neurotransmission is challenged by the majority of the in vivo motility studies; the hypothesis that ICC are mechanoreceptors has not found supportive evidence from the in vivo studies yet. More studies are needed to explain discrepancies in motility findings between the in vitro and in vivo experiments.

Roles of interstitial cells of Cajal in regulating gastrointestinal motility: in vitro versus in vivo studies

The aim of this article is to provide a better understanding of the roles of interstitial cells of Cajal (ICC) in regulating gastrointestinal motility by reviewing in vitro and in vivo physiological motility studies. Based on the in vitro studies, ICC are proposed to have the following functions: to generate slow waves, to mediate neurotransmission between the enteric nerves and the gastrointestinal muscles and to act as mechanoreceptors. However, there is limited evidence available for these hypotheses from the in vivo motility studies. In this review, we first introduce the major subtypes of ICC and their established functions. Three Kit mutant mouse and rodent models are presented and the loss of ICC subtypes in these mutants is reviewed. The physiological motility findings from various in vitro and in vivo experiments are discussed to give a critical review on the roles of ICC in generating slow waves, regulating gastrointestinal motility, mediating neural transmission and serving as mechanoreceptors. It is concluded that the role of ICC as pacemakers may be well established, but other cells may also be involved in the generation of slow waves; the theory that ICC are mediators of neurotransmission is challenged by the majority of the in vivo motility studies; the hypothesis that ICC are mechanoreceptors has not found supportive evidence from the in vivo studies yet. More studies are needed to explain discrepancies in motility findings between the in vitro and in vivo experiments.

Are interstitial cells of Cajal plurifunction cells in the gut?

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

Myoelectric activity and motility of the Roux limb after cut or uncut Roux-en-Y gastrojejunostomy

AIM: To explore the mechanisms of uncut Roux-en-Y gastrojejunostomy, which is used to decrease the occurrence of Roux stasis syndrome.

METHODS: The changes of myoelectric activity, mechanic motility and interstitial cells of Cajal (ICC) of the Roux limb after cut or uncut Roux-en-Y gastrojejunostomy were observed.

RESULTS: When compared with the cut group, the amplitude (1.15 ± 0.15 mV vs 0.48 ± 0.06 mV, P < 0.05) and frequency (14.4 ± 1.9 cpm vs 9.5 ± 1.1 cpm, P < 0.01) of slow waves and the incidence (98.2% ± 10.4% vs 56.6% ± 6.4%, P < 0.05) and amplitude (0.58 ± 0.08 mV vs 0.23 ± 0.06 mV, P < 0.01) of spike potential of the Roux limb in the uncut group were significantly higher. The migrating myoelectric complexes (MMC) phase III duration in the uncut group was significantly prolonged (6.5 ± 1.1 min vs 4.4 ± 0.8 min, P < 0.05), while the MMC cycle obviously shortened (42.5 ± 6.8 vs 55.3 ± 8.2 min, P < 0.05). Both gastric emptying rate (65.5% ± 7.9% vs 49.3% ± 6.8%, P < 0.01) and intestinal impelling ratio (53.4% ± 7.4% vs 32.2% ± 5.4%, P < 0.01) in the uncut group were significantly increased. The contractile force index of the isolated jejunal segment in the uncut group was significantly higher (36.8 ± 5.1 vs 15.3 ± 2.2, P < 0.01), and the expression of c-kit mRNA was significantly increased in the uncut group (0.82 ± 0.11 vs 0.35 ± 0.06, P < 0.01).

CONCLUSION: Uncut Roux-en-Y gastrojejunostomy may lessen the effects of operation on myoelectric activity such as slow waves, spike potential, and MMC, decrease the impairment of gastrointestinal motility, and remarkably increase the expression of c-kit mRNA.

Systematic review: applications and future of gastric electrical stimulation

BACKGROUND

Over the past 20 years, gastric electrical stimulation has received increasing attention among researchers and clinicians.

AIM

To give a systematic review on the effects, mechanisms and applications of gastric electrical stimulation.

METHODS

Medline was used to identify the articles to be included in this review. Key words used for the search included gastric electrical stimulation, gastric pacing, electrical stimulation, stomach, gastrointestinal motility, central nervous system, gastroparesis, nausea and vomiting; obesity and weight loss. Combinational uses of these keywords were made to identify relevant articles. Most of the articles included in this review ranged from 1985 to 2006.

RESULTS

Based on the general search, the review was structured as follows: (i) peripheral and central effects and mechanisms of gastric electrical stimulation; (ii) clinical applications of gastric electrical stimulation for gastroparesis and obesity and (iii) future development of gastric electrical stimulation.

CONCLUSIONS

Great progress has been made during the past decades. Gastric electrical stimulation has been shown to be effective in normalizing gastric dysrhythmia, accelerating gastric emptying and improving nausea and vomiting. Implantable device has been made available for treating gastroparesis as well as obesity. However, development of a new device and controlled clinical studies are required to further prove clinical efficacy of gastric electrical stimulation.

Roles of interstitial cells of Cajal in intestinal transit and exogenous electrical pacing

The aims of this study were to investigate the role of interstitial cells of Cajal (ICCs) on small intestinal transit and its responses to exogenous pacing in W/W(v) mice. Eleven W/W(v) mice and their controls implanted with four pairs of gastrointestinal electrodes were used for testing the entrainment of slow waves. Another 20 W/W(v) mice and their controls equipped with a duodenal catheter and one pair of intestinal electrodes were used to test small intestinal transit represented by the geometric center (GC). Results were as follows. (1) The effect of pacing on slow wave frequency was sustained only in controls, and not in W/W(v) mice. (2) Both gastric and intestinal slow waves were completely entrained in controls and W/W(v) mice. Higher energy was required for pacing the stomach than the small intestine. (3) There was no significant difference in small intestinal transit between the controls and the W/W(v) mice (GC: 5.4 vs. 5.5). (4) Pacing showed no effects on small intestinal transit in either wild-type (GC: 5.4 vs. 5.6) or W/W(v) mice (GC: 5.5 vs. 5.7). We conclude that myenteric ICCs may not play an important role in the regulation of small intestinal transit in conscious mice. Gastric and intestinal pacing can be achieved without ICCs.

Caveolae and calcium handling, a review and a hypothesis

Caveolae are associated with molecules crucial for calcium handling. This review considers the roles of caveolae in calcium handling for smooth muscle and interstitial cells of Cajal (ICC). Structural studies showed that the plasma membrane calcium pump (PMCA), a sodium-calcium exchanger (NCX1), and a myogenic nNOS appear to be colocalized with caveolin I, the main constituent of these caveolae. Voltage dependent calcium channels (VDCC) are associated but not co-localized with caveolin 1, as are proteins of the peripheral sarcoplasmic reticulum (SR) such as calreticulin. Only the nNOS is absent from caveolin 1 knockout animals. Functional studies in calcium free media sugest that a source of calcium in tonic smooth muscles exists, partly sequestered from extracellular EGTA. This source supported sustained contractions to carbachol using VDCC and dependent on activity of the SERCA pump. This source is postulated to be caveolae, near peripheral SR. New evidence, presented here, suggests that a similar source exists in phasic smooth muscle of the intestine and its ICC. These results suggest that caveolae and peripheral SR are a functional unit recycling calcium through VDCC and controlling its local concentration. Calcium handling molecules associated with caveolae in smooth muscle and ICC were identified and their possible functions also reviewed.

Novel type of interstitial cell (Cajal-like) in human fallopian tube

We describe here--presumably for the first time--a Cajal-like type of tubal interstitial cells (t-ICC), resembling the archetypal enteric ICC. t-ICC were demonstrated in situ and in vitro on fresh preparations (tissue cryosections and primary cell cultures) using methylene-blue, crystal-violet, Janus-Green B or MitoTracker-Green FM Probe vital stainings. Also, t-ICC were identified in fixed specimens by light microscopy (methylene-blue, Giemsa, trichrome stainings, Gomori silver-impregnation) or transmission electron microscopy (TEM). The positive diagnosis of t-ICC was strengthened by immunohistochemistry (IHC; CD117/c-kit+ and other 14 antigens) and immunofluorescence (IF; CD117/c-kit+ and other 7 antigens). The spatial density of t-ICC (ampullar-segment cryosections) was 100-150 cells/mm2. Non-conventional light microscopy (NCLM) of Epon semithin-sections revealed a network-like distribution of t-ICC in lamina propria and smooth muscle meshwork. t-ICC appeared located beneath of epithelium, in a 10-15 microm thick 'belt', where 18+/-2% of cells were t-ICC. In the whole lamina propria, t-ICC were about 9%, and in muscularis approximately 7%. In toto, t-ICC represent ~8% of subepithelial cells, as counted by NCLM. In vitro, t-ICC were 9.9+/-0.9% of total cell population. TEM showed that the diagnostic 'gold standard' (Huizinga et al., 1997) is fulfilled by 'our' t-ICC. However, we suggest a 'platinum standard', adding a new defining criterion- characteristic cytoplasmic processes (number: 1-5; length: tens of microm; thickness: < or =0.5 microm; aspect: moniliform; branching: dichotomous; organization: network, labyrinthic-system). Quantitatively, the ultrastructural architecture of t-ICC is: nucleus, 23.6+/-3.2% of cell volume, with heterochromatin 49.1+/-3.8%; mitochondria, 4.8+/-1.7%; rough and smooth endoplasmic-reticulum (1.1+/-0.6%, 1.0+/-0.2%, respectively); caveolae, 3.4+/-0.5%. We found more caveolae on the surface of cell processes versus cell body, as confirmed by IF for caveolins. Occasionally, the so-called 'Ca2+-release units' (subplasmalemmal close associations of caveolae+endoplasmic reticulum+mitochondria) were detected in the dilations of cell processes. Electrophysiological single unit recordings of t-ICC in primary cultures indicated sustained spontaneous electrical activity (amplitude of membrane potentials: 57.26+/-6.56 mV). Besides the CD117/c-kit marker, t-ICC expressed variously CD34, caveolins 1&2, alpha-SMA, S-100, vimentin, nestin, desmin, NK-1. t-ICC were negative for: CD68, CD1a, CD62P, NSE, GFAP, chromogranin-A, PGP9.5, but IHC showed the possible existence of (neuro)endocrine cells in tubal interstitium. We call them 'JF cells'. In conclusion, the identification of t-ICC might open the door for understanding some tubal functions, e.g. pace-making/peristaltism, secretion (auto-, juxta- and/or paracrine), regulation of neurotransmission (nitrergic/purinergic) and intercellular signaling, via the very long processes. Furthermore, t-ICC might even be uncommitted bipotential progenitor cells.