Dynamics of inhibitory co-transmission, membrane potential and pacemaker activity determine neuromyogenic function in the rat colon

Contractility of isolated colonic smooth muscle strips from rats treated with cancer chemotherapy: differential effects of cisplatin and vincristine

Background

Certain antineoplastic drugs cause gastrointestinal disorders even after the end of treatment. Enteric neuropathy has been associated with some of these alterations. Our goal was to assess the impact of repeated treatment with cisplatin and vincristine on the contractility of circular and longitudinal muscle strips isolated from the rat colon.

Methods

Two cohorts of male rats were used: in cohort 1, rats received one intraperitoneal (ip) injection of saline or cisplatin (2 mg kg-1 week-1) on the first day of weeks 1-5; in cohort 2, rats received two cycles of five daily ip injections (Monday to Friday, weeks 1-2) of saline or vincristine (0.1 mg kg-1 day-1). Body weight and food and water intake were monitored throughout the study. One week after treatment, responses of colonic smooth muscle strips to acetylcholine (10-9-10-5 M) and electrical field stimulation (EFS, 0.1-20 Hz), before and after atropine (10-6 M), were evaluated in an organ bath.

Results

Both drugs decreased body weight gain. Compared to saline, cisplatin significantly decreased responses of both longitudinal and circular smooth muscle strips to EFS, whereas vincristine tended to increase them, although in a non-significant manner. No differences were observed in the muscle response to acetylcholine. Atropine abolished the contractile responses induced by acetylcholine, although those induced by EFS were only partially reduced in the presence of atropine.

Conclusion

The findings suggest that although both drugs cause the development of enteric neuropathy, this seems to have a functional impact only in cisplatin-treated animals. Understanding the effects of chemotherapy on gastrointestinal motor function is vital for enhancing the quality of life of cancer patients.

Complementary mechanisms of modulation of spontaneous phasic contractions by the gaseous signalling molecules NO, H2S, HNO and the polysulfide Na2S3 in the rat colon

OBJECTIVES

Reactive oxygen and nitrogen species may be produced during inflammation leading to the formation of NO, H2S or HNO. Enzymes such as iNOS, CSE and CBS might also be responsible for polysulfide production. Since these signalling molecules might have an impact on colonic motility, the aim of this study was to compare their effect on rat colonic slow phasic contractions (SPC).

METHODS

Organ bath measurements with strips obtained from rat proximal colon were performed using the polysulfide Na2S3, sodium nitroprusside (NaNP), sodium hydrogen sulfide (NaHS), Angeli's salt as NO, H2S, and HNO donors, respectively. TTX (1 µM) was used to block neuronal activity.

RESULTS

All four molecules, concentration-dependently, inhibited the amplitude and frequency of SPC both in the circular and longitudinal muscle layer. The relative potency was NaNP>Angeli's salt>NaHS>Na2S3. The inhibitory response induced by NaNP (1 µM) and Angeli's salt (50 µM) was reversed by ODQ (10 µM) whereas the inhibitory effect of NaHS (1 mM) was reversed by apamin (1 µM) and glibenclamide (10 µM). Na2S3 (1 mM) response was partially reversed by apamin (1 µM) and glibenclamide (10 µM). High concentrations of Na2S3 caused an increase in tone. Low concentrations of NaHS or Na2S3 did not potentiate NaNP responses.

CONCLUSIONS

All signalling molecules inhibit SPC in both muscle layers. The effect is independent of neural activity and involves guanylyl cyclase (NO and HNO) and SKCa and KATP channels (NaHS or Na2S3). Other pathways might also be involved in Na2S3 responses. Accordingly, complementary mechanisms of inhibition might be attributable to these signalling molecules.

Naringenin modulates Cobalt activities on gut motility through mechanosensors and serotonin signalling

IntroductionCobalt chloride-(CoCl₂) exerts beneficial and toxic activities depending on dose however Naringenin-(Nar) a flavonoid, chelates heavy metals. Absorption of ingested heavy metals, or chelates are dependent on gut motility (gastric emptying and intestinal transit time) and mechanosensor regulation. Literature is vague on CoCl₂ activities on gut motility and mechanosensor nor probable chelating actions with naringenin which was investigated in this study.MethodOne hundred male Wistar rats were grouped viz; A to D (25, 62, 150 and 300 mg/kg CoCl₂), E to H doses of CoCl₂+Nar (50 mg/kg), I-Narigenin and J-Control. Gastric emptying and intestinal transit time were evaluated by day eight, intestinal tissue assayed for biochemical, histological and immunohistochemistry reactivity.ResultCoCl₂ significantly increased Gastric emptying (150 and 300 mg/kg) and Intestinal transit time unlike Naringenin. CoCl₂ (150 mg/kg) significantly increased Catalase and Nitric oxide but ameliorated by Naringenin. ATPase activities significantly increased in 150 mg/kg-CoCl₂ but ameliorated by Naringenin. Carbonyl levels increased in all CoCl₂+Nar groups. High Enterochromaffin-cell count in 25 and 62 mg/kg-CoCl₂ were ameliorated by Naringenin. Serotonin immunoreactivity increased in CoCl₂ (25, 62, 300 mg/kg) but reduced in CoCl₂+Nar groups.ConclusionCobalt chloride enhanced gastric motility via increased mechanosensor activities and serotonin expression at low doses. Naringenin ameliorated toxicity of high cobalt chloride via metal-flavonoid chelates.

The Role of H2S in the Gastrointestinal Tract and Microbiota

The pathways and mechanisms of the production of H₂S in the gastrointestinal tract are briefly described, including endogenous H₂S produced by the organism and H₂S from microorganisms in the gastrointestinal tract. In addition, the physiological regulatory functions of H₂S on gastrointestinal motility, sensation, secretion and absorption, endocrine system, proliferation and differentiation of stem cells, and the possible mechanisms involved are introduced. In view of the complexity of biosynthesis, physiological roles, and the mechanism of H₂S, this chapter focuses on the interactions and dynamic balance among H₂S, gastrointestinal microorganisms, and the host. Finally, we focus on some clinical gastrointestinal diseases, such as inflammatory bowel disease, colorectal cancer, functional gastrointestinal disease, which might occur or develop when the above balance is broken. Pharmacological regulation of H₂S or the intestinal microorganisms related to H₂S might provide new therapeutic approaches for some gastrointestinal diseases.

Neurotransmitters responsible for purinergic motor neurotransmission and regulation of GI motility

Classical concepts of peripheral neurotransmission were insufficient to explain enteric inhibitory neurotransmission. Geoffrey Burnstock and colleagues developed the idea that ATP or a related purine satisfies the criteria for a neurotransmitter and serves as an enteric inhibitory neurotransmitter in GI muscles. Cloning of purinergic receptors and development of specific drugs and transgenic mice have shown that enteric inhibitory responses depend upon P2Y₁ receptors in post-junctional cells. The post-junctional cells that transduce purinergic neurotransmitters in the GI tract are PDGFRα⁺ cells and not smooth muscle cells (SMCs). PDGFRα⁺ cells express P2Y₁ receptors, are activated by enteric inhibitory nerve stimulation and generate Ca²⁺ oscillations, express small-conductance Ca²⁺-activated K⁺ channels (SK3), and generate outward currents when exposed to P2Y₁ agonists. These properties are consistent with post-junctional purinergic responses, and similar responses and effectors are not functional in SMCs. Refinements in methodologies to measure purines in tissue superfusates, such as high-performance liquid chromatography (HPLC) coupled with etheno-derivatization of purines and fluorescence detection, revealed that multiple purines are released during stimulation of intrinsic nerves. β-NAD⁺ and other purines, better satisfy criteria for the purinergic neurotransmitter than ATP. HPLC has also allowed better detection of purine metabolites, and coupled with isolation of specific types of post-junctional cells, has provided new concepts about deactivation of purine neurotransmitters. In spite of steady progress, many unknowns about purinergic neurotransmission remain and require additional investigation to understand this important regulatory mechanism in GI motility.

The asymmetric innervation of the circular and longitudinal muscle of the mouse colon differently modulates myogenic slow phasic contractions

BACKGROUND

Neuromuscular transmission has been extensively studied in the circular layer of the mouse colon where a co-transmission of purines acting on P2Y₁ receptors and NO has been previously described. However, the corresponding mechanisms in the longitudinal layer are less known.

METHODS

Electrophysiological and myography techniques were used to evaluate spontaneous phasic contractions (SPC) and neural-mediated responses in the proximal, mid, and distal colon devoid of CD1 mice. Immunohistochemistry against c-kit and PDGFRα was performed in each colonic segment.

KEY RESULTS

SPC were recorded in both muscle layers at a similar frequency being about four contractions per minute (c.p.m.) in the proximal and distal colon compared to the mid colon (2 c.p.m.). In non-adrenergic, non-cholinergic conditions, L-NNA (1 mmol/L) increased contractility in the circular but not in the longitudinal layer. In the longitudinal muscle, both electrophysiological and mechanical neural-mediated inhibitory responses were L-NNA and ODQ (10 µmol/L) sensitive. NaNP (1 µmol/L) caused cessation of SPC and the response was blocked by ODQ. Neither ADPßS (10 µmol/L) nor CYPPA (10 µmol/L), which both targeted the purinergic pathway, altered longitudinal contractions. PDGFRα + cells were located in both muscle layers and were more numerous compared with cKit + cells, which both formed a heterologous cellular network. A decreasing gradient of the PDGFRα labeling was observed along the colon.

CONCLUSION

An inhibitory neural tone was absent in the longitudinal layer and neuronal inhibitory responses were mainly nitrergic. Despite the presence of PDGFRα + cells, purinergic responses were absent. Post-junctional pathways located in different cell types might be responsible for neurotransmitter transduction.

First translational consensus on terminology and definitions of colonic motility in animals and humans studied by manometric and other techniques

Alterations in colonic motility are implicated in the pathophysiology of bowel disorders, but high-resolution manometry of human colonic motor function has revealed that our knowledge of normal motor patterns is limited. Furthermore, various terminologies and definitions have been used to describe colonic motor patterns in children, adults and animals. An example is the distinction between the high-amplitude propagating contractions in humans and giant contractions in animals. Harmonized terminology and definitions are required that are applicable to the study of colonic motility performed by basic scientists and clinicians, as well as adult and paediatric gastroenterologists. As clinical studies increasingly require adequate animal models to develop and test new therapies, there is a need for rational use of terminology to describe those motor patterns that are equivalent between animals and humans. This Consensus Statement provides the first harmonized interpretation of commonly used terminology to describe colonic motor function and delineates possible similarities between motor patterns observed in animal models and humans in vitro (ex vivo) and in vivo. The consolidated terminology can be an impetus for new research that will considerably improve our understanding of colonic motor function and will facilitate the development and testing of new therapies for colonic motility disorders.

Hydrogen sulphide as a signalling molecule regulating physiopathological processes in gastrointestinal motility

The biology of H₂ S is a still developing area of research and several biological functions have been recently attributed to this gaseous molecule in many physiological systems, including the cardiovascular, urogenital, respiratory, digestive and central nervous system (CNS). H₂ S exerts anti-inflammatory effects and can be considered an endogenous mediator with potential effects on gastrointestinal motility. During the last few years, we have investigated the role of H₂ S as a regulator of gastrointestinal motility using both animal and human tissues. The aim of the present work is to review published data regarding the potential role of H₂ S as a signalling molecule regulating physiopathological processes in gastrointestinal motor function. H₂ S is endogenously produced by defined enzymic pathways in different cell types of the intestinal wall including neurons and smooth muscle. Inhibition of H₂ S biosynthesis increases motility and H₂ S donors cause smooth muscle relaxation and inhibition of propulsive motor patterns. Impaired H₂ S production has been described in animal models with gastrointestinal motor dysfunction. The mechanism(s) of action underlying these effects may include several ion channels, although no specific receptor has been identified. At this time, even though there is much experimental evidence for H₂ S as a modulator of gastrointestinal motility, we still do not have conclusive experimental evidence to definitively propose H₂ S as an inhibitory neurotransmitter in the gastrointestinal tract, causing nerve-mediated relaxation.

BPTU, an allosteric antagonist of P2Y1 receptor, blocks nerve mediated inhibitory neuromuscular responses in the gastrointestinal tract of rodents

P2Y1 receptors mediate nerve mediated purinergic inhibitory junction potentials (IJP) and relaxations in the gastrointestinal (GI) tract in a wide range of species including rodents and humans. A new P2Y1 antagonist, with a non-nucleotide structure, BPTU, has recently been described using X-ray crystallography as the first allosteric G-protein-coupled receptor antagonist located entirely outside of the helical bundle. In this study, we tested its effect on purinergic responses in the gastrointestinal tract of rodents using electrophysiological and myographic techniques. BPTU concentration dependently inhibited purinergic inhibitory junction potentials and inhibition of spontaneous motility induced by electrical field stimulation in the colon of rats (EC50 = 0.3 μM) and mice (EC50 = 0.06 μM). Mechanical inhibitory responses were also concentration-dependently blocked in the stomach of both species. Compared to MRS2500, BPTU displays a lower potency. In the rat colon nicotine induced relaxation was also blocked by BPTU. BPTU also blocked the cessation of spontaneous contractility elicited by ADPβS and the P2Y1 agonist MRS2365. We conclude that BPTU is a novel antagonist with different structural and functional properties than nucleotidic antagonists that is able to block the P2Y1 receptor located at the neuromuscular junction of the GI tract.

Changes of excitatory and inhibitory neurotransmitters in the colon of rats underwent to the wrap partial restraint stress

BACKGROUND

Animal models proposed to reproduce some of the human irritable bowel syndrome (IBS) symptoms are based on the hypothesis that psychosocial stressors play a pivotal role in the IBS etio-pathology. We investigated the wrap restraint stress (WRS) model with the aim to analyze the morphological changes of the entire colonic wall of these animals that showed some of the human IBS symptoms such as visceral hypersensitivity.

METHODS

Male Wistar rats were used and WRS was maintained for 2 h. Abdominal contractions (AC) were recorded in the colon-rectum by balloon distension. Fecal pellets were quantitated. Colonic specimens were examined by routine histology, immunohistochemistry and western blot.

KEY RESULTS

WRS animals were characterized by: (i) increase in AC number and fecal pellets mean weight; (ii) clusters of mononucleated cells, increase in eosinophilic granulocytes and mast cells in the mucosa; (iii) increase in CGRP-immunoreactive (IR) nerve fibers in the lamina propria; (iv) decrease in myenteric NK1r-IR and nNOS-IR neurons and in submucous nNOS-IR neurons; (v) decrease in SP-IR nerve fibers in the muscle wall; (vi) reduction in S100β-IR glia in the entire colonic wall; (vii) increase in CRF1r-IR myenteric neurons; (viii) no change in ChAT-IR neurons, smooth muscle cells and interstitial cells of Cajal.

CONCLUSIONS AND INFERENCES

The present results support the consistency of the WRS as a potential model where part of the human IBS signs and symptoms are reproduced. The changes in glial cells and in excitatory and inhibitory neurotransmitters might represent the substrate for the dysmotility and hypersensitivity.

Neurotensin Changes Propulsive Activity into a Segmental Motor Pattern in the Rat Colon

BACKGROUND/AIMS

Neurotensin is a gut-brain peptide with both inhibitory and excitatory actions on the colonic musculature; our objective was to understand the implications of this for motor patterns occurring in the intact colon of the rat.

METHODS

The effects of neurotensin with concentrations ranging from 0.1-100 nM were studied in the intact rat colon in vitro, by investigating spatio-temporal maps created from video recordings of colonic motility before and after neurotensin.

RESULTS

Low concentration of neurotensin (0.1-1 nM) inhibited propagating long distance contractions and rhythmic propagating motor complexes; in its place a slow propagating rhythmic segmental motor pattern developed. The neurotensin receptor 1 antagonist SR-48692 prevented the development of the segmental motor pattern. Higher concentrations of neurotensin (10 nM and 100 nM) were capable of restoring long distance contraction activity and inhibiting the segmental activity. The slow propagating segmental contraction showed a rhythmic contraction-- relaxation cycle at the slow wave frequency originating from the interstitial cells of Cajal associated with the myenteric plexus pacemaker. High concentrations given without prior additions of low concentrations did not evoke the segmental motor pattern. These actions occurred when neurotensin was given in the bath solution or intraluminally. The segmental motor pattern evoked by neurotensin was inhibited by the neural conduction blocker lidocaine.

CONCLUSIONS

Neurotensin (0.1-1 nM) inhibits the dominant propulsive motor patterns of the colon and a distinct motor pattern of rhythmic slow propagating segmental contractions develops. This motor pattern has the hallmarks of haustral boundary contractions.

The effect of levosulpiride on in vitro motor patterns in the human gastric fundus, antrum, and jejunum

BACKGROUND

Levosulpiride is a 5HT4 agonist/D2 antagonist prokinetic agent used to improve gastric emptying in patients with functional dyspepsia or gastroparesis. The aim of this study was to characterize its effect on the main in vitro motility patterns in the human fundus, antrum, and jejunum.

METHODS

Circular muscle strips from human stomach (antrum and fundus) and jejunum, obtained from 46 patients undergoing bariatric surgery, were studied using organ baths. Enteric motor neurons (EMNs) were stimulated by electrical field stimulation (EFS).

KEY RESULTS

Levosulpiride, caused an increase in the EFS-induced cholinergic contractions in the gastric antrum (+37 ± 15.18% at 100 μM, pEC50 = 4.46 ± 0.14; p < 0.05, n = 8) and jejunum (+45.4 ± 22.03% at 100 μM, pEC50 = 3.78 ± 6.81; p < 0.05, n = 5), but not in the gastric fundus. It also caused a slight decrease in tone and frequency of spontaneous contractions in the jejunum, but did not have any major effect on tone or spontaneous contractions in the stomach. It did not have any effect on EFS-induced relaxations mediated by nitric oxide (NO) in the stomach (antrum and fundus) and by NO and ATP in the jejunum.

CONCLUSIONS & INFERENCES

Our results suggest that the prokinetic effects of levosulpiride in humans are mainly due to the facilitation of the release of acetylcholine by enteric motor neurons in the gastric antrum and the jejunum.

Haustral boundary contractions in the proximal 3-taeniated rabbit colon

The rabbit proximal colon is similar in structure to the human colon. Our objective was to study interactions of different rhythmic motor patterns focusing on haustral boundary contractions, which create the haustra, using spatiotemporal mapping of video recordings. Haustral boundary contractions were seen as highly rhythmic circumferential ring contractions that propagated slowly across the proximal colon, preferentially but not exclusively in the anal direction, at ∼0.5 cycles per minute; they were abolished by nerve conduction blockers. When multiple haustral boundary contractions propagated in the opposite direction, they annihilated each other upon encounter. Ripples, myogenic propagating ring contractions at ∼9 cycles per min, induced folding and unfolding of haustral muscle folds, creating an anarchic appearance of contractile activity, with different patterns in the three intertaenial regions. Two features of ripple activity were prominent: frequent changes in propagation direction and the occurrence of dislocations showing a frequency gradient with the highest intrinsic frequency in the distal colon. The haustral boundary contractions showed an on/off/on/off pattern at the ripple frequency, and the contraction amplitude at any point of the colon showed waxing and waning. The haustral boundary contractions are therefore shaped by interaction of two pacemaker activities hypothesized to occur through phase-amplitude coupling of pacemaker activities from interstitial cells of Cajal of the myenteric plexus and of the submuscular plexus. Video evidence shows the unique role haustral folds play in shaping contractile activity within the haustra. Muscarinic agents not only enhance the force of contraction, they can eliminate one and at the same time induce another neurally dependent motor pattern.

P2Y(1) receptors mediate purinergic relaxation in the equine pelvic flexure

In the equine large intestine, the knowledge of the basic mechanisms underlying motility function is crucial to properly treat motility disorders. P2Y1 receptors are responsible for mediating purinergic colonic relaxation in several species. In vitro experimental studies of the circular muscle from the equine pelvic flexure (n = 6) were performed to characterize inhibitory and excitatory neuromuscular transmission. Electrophysiological studies showed that electrical field stimulation (EFS) evoked biphasic inhibitory junction potentials (IJPs) in smooth muscle cells: a fast IJP (IJPf) followed by a sustained IJP (IJPs). IJPs was sensitive to L-NNA 1 mM (a nitric oxide synthase inhibitor) (P <0.01), while IJPf was abolished by MRS2500 1 µM (a P2Y1 receptor antagonist) (P <0.001). EFS (5 Hz for 2 min) in the organ bath inhibited rhythmic contractions to 3.0 ± 2.5% of basal area under the curve (P <0.0001). EFS under MRS2500 1 µM or L-NNA 1 mM incubation inhibited contractions to 6.0 ± 2.8% (P <0.05) and 24.4 ± 11.3% respectively (P <0.05). Combination of MRS2500 1 µM and L-NNA 1 mM completely reversed the EFS-induced inhibition of colonic motility. Non-nitrergic, non-purinergic conditions were used to reveal voltage-dependent EFS-induced contractions sensitive to atropine 1 µM (P <0.001) and, therefore, cholinergic. In conclusion, nerve-mediated relaxation and contraction in the equine pelvic flexure involve the same mechanisms as those observed in the human colon. P2Y1 receptors mediate purinergic relaxations and are potential targets for the treatment of equine colonic motor disorders.

Inverse gradient of nitrergic and purinergic inhibitory cotransmission in the mouse colon

AIM

Gastrointestinal smooth muscle relaxation is accomplished by the neural corelease of ATP or a related purine and nitric oxide. Contractions are triggered by acetylcholine and tachykinins. The aim of this work was to study whether regional differences in neurotransmission could partially explain the varied physiological roles of each colonic area.

METHODS

We used electrophysiological and myography techniques to evaluate purinergic (L-NNA 1 mm incubated tissue), nitrergic (MRS2500 0.3 μm incubated tissue) and cholinergic neurotransmission (L-NNA 1 mm and MRS2500 0.3 μm incubated tissue) in the proximal, mid and distal colon of CD1 mice (n = 42).

RESULTS

Purinergic electrophysiological responses elicited by single pulses (28 V) were greater in the distal (IJPfMAX = -35.3 ± 2.2 mV), followed by the mid (IJPfMAX = -30.6 ± 1.0 mV) and proximal (IJPfMAX = -11.7 ± 1.1 mV) colon. In contrast, nitrergic responses decreased from the proximal colon (IJPsMAX = -11.4 ± 1.1 mV) to the mid (IJPsMAX = -9.1 ± 0.4 mV), followed by the distal colon (IJPsMAX = -1.8 ± 0.3 mV). A similar rank of order was observed in neural mediated inhibitory mechanical responses including electrical field stimulation-mediated responses and neural tone. ADPβs concentration-response curve was shifted to the left in the distal colon. In contrast, NaNP responses did not differ between regions. Cholinergic neurotransmission elicited contractions of a similar amplitude throughout the colon.

CONCLUSION

An inverse gradient of purinergic and nitrergic neurotransmission exists through the mouse colon. The proximal and mid colon have a predominant nitrergic neurotransmission probably due to the fact that their storage function requires sustained relaxations. The distal colon, in contrast, has mainly purinergic neurotransmission responsible for the phasic relaxations needed to propel dehydrated faeces.

Motor patterns of the small intestine explained by phase-amplitude coupling of two pacemaker activities: the critical importance of propagation velocity

Phase-amplitude coupling of two pacemaker activities of the small intestine, the omnipresent slow wave activity generated by interstitial cells of Cajal of the myenteric plexus (ICC-MP) and the stimulus-dependent rhythmic transient depolarizations generated by ICC of the deep muscular plexus (ICC-DMP), was recently hypothesized to underlie the orchestration of the segmentation motor pattern. The aim of the present study was to increase our understanding of phase-amplitude coupling through modeling. In particular the importance of propagation velocity of the ICC-DMP component was investigated. The outcome of the modeling was compared with motor patterns recorded from the rat or mouse intestine from which propagation velocities within the different patterns were measured. The results show that the classical segmentation motor pattern occurs when the ICC-DMP component has a low propagation velocity (<0.05 cm/s). When the ICC-DMP component has a propagation velocity in the same order of magnitude as that of the slow wave activity (∼1 cm/s), cluster type propulsive activity occurs which is in fact the dominant propulsive activity of the intestine. Hence, the only difference between the generation of propagating cluster contractions and the Cannon-type segmentation motor pattern is the propagation velocity of the low-frequency component, the rhythmic transient depolarizations originating from the ICC-DMP. Importantly, the proposed mechanism explains why both motor patterns have distinct rhythmic waxing and waning of the amplitude of contractions. The hypothesis is brought forward that the velocity is modulated by neural regulation of gap junction conductance within the ICC-DMP network.

Induction of rhythmic transient depolarizations associated with waxing and waning of slow wave activity in intestinal smooth muscle

Cannon described in 1902 the segmentation motor activity of the small intestine (Canon WB. J Med Res 7: 72-75, 1902). This motor pattern can arise when low-frequency transient depolarizations are evoked in the interstitial cells of Cajal associated with the deep muscular plexus (ICC-DMP) network, which then affect the omnipresent slow wave activity: changing its regular amplitude into a waxing and waning pattern. The objective of the present study was to investigate physiological stimuli that could induce the low-frequency component. Intracellular recordings were obtained from circular muscle with or without attached mucosa. Decanoic acid (1 mM) and butyric acid (10 mM) both evoked low-frequency transient depolarizations but through different mechanisms. Decanoic acid-induced waxing and waning was initiated by purely myogenic means when perfused onto exposed circular muscle. Butyric acid required the intact mucosa and uninhibited neural activity to elicit the low-frequency response. Evidence is provided that the transient rhythmic depolarizations occur in the absence of interstitial cells of Cajal associated with the myenteric plexus (ICC-MP). Onset of the slow transient depolarizations was stimulated by addition of N(ω)-nitro-l-arginine (l-NNA; 100 μM); thus the low-frequency component seems to be under chronic inhibition by nitric oxide. Excitatory tachykinergic stimulation induced the low-frequency component since substance P (0.5 μM) evoked it in the presence of neural blockade. In summary, interplay between two networks of myogenic pacemakers, neural activity, and nutrient factors such as fatty acids plays a role in the generation of the rhythmic low-frequency component that is essential for the development of the checkered segmentation motor pattern.

Purinergic neuromuscular transmission in the gastrointestinal tract; functional basis for future clinical and pharmacological studies

Nerve-mediated relaxation is necessary for the correct accomplishment of gastrointestinal (GI) motility. In the GI tract, NO and a purine are probably released by the same inhibitory motor neuron as inhibitory co-transmitters. The P2Y1 receptor has been recently identified as the receptor responsible for purinergic smooth muscle hyperpolarization and relaxation in the human gut. This finding has been confirmed in P2Y1 -deficient mice where purinergic neurotransmission is absent and transit time impaired. However, the mechanisms responsible for nerve-mediated relaxation, including the identification of the purinergic neurotransmitter(s) itself, are still debatable. Possibly different mechanisms of nerve-mediated relaxation are present in the GI tract. Functional demonstration of purinergic neuromuscular transmission has not been correlated with structural studies. Labelling of purinergic neurons is still experimental and is not performed in routine pathology studies from human samples, even when possible neuromuscular impairment is suspected. Accordingly, the contribution of purinergic neurotransmission in neuromuscular diseases affecting GI motility is not known. In this review, we have focused on the physiological mechanisms responsible for nerve-mediated purinergic relaxation providing the functional basis for possible future clinical and pharmacological studies on GI motility targeting purine receptors.