Nitric oxide-sensitive guanylyl cyclase is dispensable for nitrergic signaling and gut motility in mouse intestinal smooth muscle

Therapeutic Potential of Foodborne Indole Derived from Chinese Stinky Tofu in Reducing Intestinal Inflammation and Enhancing Barrier Function to Mitigate Alcoholic Liver Injury

Indole, a compound in Chinese stinky tofu (ST), acts as a ligand for the aryl hydrocarbon receptor (AHR). Despite extensive research on prebiotic compounds, indole's specific role in ST remains unexplored. This study used an ethanol gavage method to create an ALD (alcoholic liver disease) mouse model and investigate dietary indole's effects on the intestinal barrier. Our findings indicate that after 6 weeks of being fed ST, the indole present (2 mg/day) robustly activated the intestinal AHR, upregulating its target gene, CYP1A1 (cytochrome P450 1A1 enzyme). This activation significantly reduced intestinal permeability, mitigated alcohol-induced oxidative stress and inflammation, and restored intestinal barrier function. Consequently, the study demonstrates that foodborne indole substantially reduces alcohol absorption and lowers the expression levels of liver inflammation-related factors, thereby slowing the progression of ALD. These results highlight indole's therapeutic potential for treating ALD and its role in developing functional foods.

Anti-Fibrotic and Anti-Inflammatory Role of NO-Sensitive Guanylyl Cyclase in Murine Lung

Pulmonary fibrosis is a chronic and progressive disease with limited therapeutic options. Nitric oxide (NO) is suggested to reduce the progression of pulmonary fibrosis via NO-sensitive guanylyl cyclase (NO-GC). The exact effects of NO-GC during pulmonary fibrosis are still elusive. Here, we used a NO-GC knockout mouse (GCKO) and examined fibrosis and inflammation after bleomycin treatment. Compared to wildtype (WT), GCKO mice showed an increased fibrotic reaction, as myofibroblast occurrence (p = 0.0007), collagen content (p = 0.0006), and mortality (p = 0.0009) were significantly increased. After fibrosis induction, lymphocyte accumulations were observed in the lungs of GCKO but not in WT littermates. In addition, the total number of immune cells, specifically lymphocytes (p = <0.0001) and neutrophils (p = 0.0047), were significantly higher in the bronchoalveolar lavage fluid (BALF) of GCKO animals compared to WT, indicating an increased inflammatory response in the absence of NO-GC. The pronounced fibrotic response in GCKO mice was paralleled by significantly increased levels of transforming growth factor β (TGFβ) in BALF (p = 0.0207), which correlated with the total number of immune cells. Taken together, our data show the effect of NO-GC deletion in the pathology of lung fibrosis and the effect on immune cells in BALF. In summary, our results show that NO-GC has anti-inflammatory and anti-fibrotic properties in the murine lung, very likely by attenuating TGFβ-mediated effects.

NO-sensitive guanylyl cyclase discriminates pericyte-derived interstitial from intra-alveolar myofibroblasts in murine pulmonary fibrosis

BACKGROUND

The origin of αSMA-positive myofibroblasts, key players within organ fibrosis, is still not fully elucidated. Pericytes have been discussed as myofibroblast progenitors in several organs including the lung.

METHODS

Using tamoxifen-inducible PDGFRβ-tdTomato mice (PDGFRβ-CreER^T2; R26tdTomato) lineage of lung pericytes was traced. To induce lung fibrosis, a single orotracheal dose of bleomycin was given. Lung tissue was investigated by immunofluorescence analyses, hydroxyproline collagen assay and RT-qPCR.

RESULTS

Lineage tracing combined with immunofluorescence for nitric oxide-sensitive guanylyl cyclase (NO-GC) as marker for PDGFRβ-positive pericytes allows differentiating two types of αSMA-expressing myofibroblasts in murine pulmonary fibrosis: (1) interstitial myofibroblasts that localize in the alveolar wall, derive from PDGFRβ⁺ pericytes, express NO-GC and produce collagen 1. (2) intra-alveolar myofibroblasts which do not derive from pericytes (but express PDGFRβ de novo after injury), are negative for NO-GC, have a large multipolar shape and appear to spread over several alveoli within the injured areas. Moreover, NO-GC expression is reduced during fibrosis, i.e., after pericyte-to-myofibroblast transition.

CONCLUSION

In summary, αSMA/PDGFRβ-positive myofibroblasts should not be addressed as a homogeneous target cell type within pulmonary fibrosis.

A novel beneficial role of humanin on intestinal apoptosis and dysmotility in a rat model of ischemia reperfusion injury

A prevalent clinical problem including sepsis, shock, necrotizing enterocolitis, and mesenteric thrombosis is intestinal ischemia/reperfusion (I/R) injury. Humanin (HN), a recently identified mitochondrial polypeptide, exhibits antioxidative and antiapoptotic properties. This work aimed to study the role of HN in a model of experimental intestinal I/R injury and its effect on associated dysmotility. A total of 36 male adult albino rats were allocated into 3 equal groups. Sham group: merely a laparotomy was done. I/R group: for 1 h, clamping of the superior mesenteric artery was done, and then reperfusion was allowed for 2 h later. HN-I/R group: rats underwent ischemia and reperfusion, and 30 min before the reperfusion, they received an intraperitoneal injection of 252 μg/kg of HN. Small intestinal motility was evaluated, and jejunal samples were got for biochemical and histological analysis. I/R group showed elevation of intestinal NO, MDA, TNF- α, and IL-6 and decline of GPx and SOD levels. Furthermore, histologically, there were destructed jejunal villi especially their tips and increased tissue expression of caspase-3 and i-NOS, in addition to reduced small intestinal motility. Compared to I/R group, HN-I/R group exhibited decrease intestinal levels of NO, MDA, TNF- α, and IL-6 and increase GPx and SOD. Moreover, there was noticeable improvement of the histopathologic features and decreased caspase-3 and iNOS immunoreactivity, beside enhanced small intestinal motility. HN alleviates inflammation, apoptosis, and intestinal dysmotility encouraged by I/R. Additionally, I/R-induced apoptosis and motility alterations depend partly on the production of nitric oxide.

Identification of evodiamine and rutecarpine as novel TMEM16A inhibitors and their inhibitory effects on peristalsis in isolated Guinea-pig ileum

The transmembrane member 16A (TMEM16A)-encoded Ca2+-activated Cl- channel (CaCC) is expressed in interstitial cells of Cajal (ICCs) and involved in the generation of the slow-wave currents of gastrointestinal (GI) smooth muscles. TMEM16A modulators have been shown to positively or negatively regulate the contraction of gastrointestinal smooth muscle. Therefore, targeting the pharmacological modulation of TMEM16A may represent a novel treatment approach for gastrointestinal dysfunctions such as constipation and diarrhoea. In this study, evodiamine and rutecarpine were extracted from the traditional Chinese medicine Evodia rutaecarpa and identified as novel TMEM16A inhibitors with comparable inhibitory effects. Their effects on intestinal peristalsis were examined. Whole-cell patch clamp results show that evodiamine and rutecarpine inhibited TMEM16A Cl- currents in CHO cells. The half-maximal inhibition values (IC50) of evodiamine and rutecarpine on TMEM16A Cl- currents were 11.8 ± 1.3 μΜ and 9.2 ± 0.4 μM, and the maximal effect values (Emax) were 95.8 ± 5.1% and 99.1 ± 1.6%, respectively. The Lys384, Thr385, and Met524 in TMEM16A are critical for evodiamine and rutecarpine's inhibitory effects. Further functional studies show that both evodiamine and rutecarpine can significantly suppress the peristalsis in isolated guinea-pig ileum. These findings demonstrate that evodiamine and rutecarpine are new TMEM16A inhibitors and support the regulation effect of TMEM16A modulators on gastrointestinal motility.

Differentiated PDGFRα-Positive Cells: A Novel In-Vitro Model for Functional Studies of Neuronal Nitric Oxide Synthase

It is evident that depletion of interstitial cells and dysfunction of nitric oxide (NO) pathways are key players in development of several gastrointestinal (GI) motility disorders such as diabetic gastroparesis (DGP). One of the main limitations of DGP research is the lack of isolation methods that are specific to interstitial cells, and therefore conducting functional studies is not feasible. The present study aims (i) to differentiate telomerase transformed mesenchymal stromal cells (iMSCs) into platelet-derived growth factor receptor-α-positive cells (PDGFRα-positive cells) using connective tissue growth factor (CTGF) and L-ascorbic acids; (ii) to investigate the effects of NO donor and inhibitor on the survival rate of differentiated PDGFRα-positive cells; and (iii) to evaluate the impact of increased glucose concentrations, mimicking diabetic hyperglycemia, on the gene expression of neuronal nitric oxide synthase (nNOS). A fibroblastic differentiation-induction medium supplemented with connective tissue growth factor was used to differentiate iMSCs into PDGFRα-positive cells. The medium was changed every day for 21 days to maintain the biological activity of the growth factors. Gene and protein expression, scanning electron and confocal microscopy, and flow cytometry analysis of several markers were conducted to confirm the differentiation process. Methyl tetrazolium cell viability, nitrite measurement assays, and immunostaining were used to investigate the effects of NO on PDGFRα-positive cells. The present study, for the first time, demonstrated the differentiation of iMSCs into PDGFRα-positive cells. The outcomes of the functional studies showed that SNAP (NO donor) increased the survival rate of differentiated PDGFRα-positive cells whereas LNNA (NO inhibitor) attenuated these effects. Further experimentations revealed that hyperglycemia produced a significant increase in expression of nNOS in PDGFRα-positive cells. Differentiation of iMSCs into PDGFRα-positive cells is a novel model to conduct functional studies and to investigate the involvement of NO pathways. This will help in identifying new therapeutic targets for treatment of DGP.

The effect of Xenin25 on spontaneous circular muscle contractions of rat distal colon in vitro

Xenin25 has a variety of physiological functions in the Gastrointestinal (GI) tract, including ion transport and motility. However, the motility responses in the colon induced by Xenin25 remain poorly understood. Therefore, the effect of Xenin25 on the spontaneous circular muscle contractions of the rat distal colon was investigated using organ bath chambers and immunohistochemistry. Xenin25 induced the inhibition followed by postinhibitory spontaneous contractions with a higher frequency in the rat distal colon. This inhibitory effect of Xenin25 was significantly suppressed by TTX but not by atropine. The inhibitory time (the duration of inhibition) caused by Xenin25 was shortened by the NTSR1 antagonist SR48692, the NK1R antagonist CP96345, the VPAC2 receptor antagonist PG99-465, the nitric oxide-sensitive guanylate-cyclase inhibitor ODQ, and the Ca2+ -dependent K+ channel blocker apamin. The higher frequency of postinhibitory spontaneous contractions induced by Xenin25 was also attenuated by ODQ and apamin. SP-, NOS-, and VIP-immunoreactive neurons were detected in the myenteric plexus (MP) of the rat distal colon. Small subsets of the SP-positive neurons were also Calbindin positive. Most of the VIP-positive neurons were also NOS positive, and small subsets of the NK1R-positive neurons were also VIP positive. Based on the present results, we propose the following mechanism. Xenin25 activates neuronal NTSR1 on the SP neurons of IPANs, and transmitters from the VIP and apamin-sensitive NO neurons synergistically inhibit the spontaneous circular muscle contractions via NK1R. Subsequently, the postinhibitory spontaneous contractions are induced by the offset of apamin-sensitive NO neuron activation via the interstitial cells of Cajal. In addition, Xenin25 also activates the muscular NTSR1 to induce relaxation. Thus, Xenin25 is considered to be an important modulator of post prandial circular muscle contraction of distal colon since the release of Xenin25 from enteroendocrine cells is stimulated by food intake.

Phosphodiesterases in the Liver as Potential Therapeutic Targets of Cirrhotic Portal Hypertension

Liver cirrhosis is a frequent condition with high impact on patients' life expectancy and health care systems. Cirrhotic portal hypertension (PH) gradually develops with deteriorating liver function and can lead to life-threatening complications. Other than an increase in intrahepatic flow resistance due to morphological remodeling of the organ, a functional dysregulation of the sinusoids, the smallest functional units of liver vasculature, plays a pivotal role. Vascular tone is primarily regulated by the nitric oxide-cyclic guanosine monophosphate (NO-cGMP) pathway, wherein soluble guanylate cyclase (sGC) and phosphodiesterase-5 (PDE-5) are key enzymes. Recent data showed characteristic alterations in the expression of these regulatory enzymes or metabolite levels in liver cirrhosis. Additionally, a disturbed zonation of the components of this pathway along the sinusoids was detected. This review describes current knowledge of the pathophysiology of PH with focus on the enzymes regulating cGMP availability, i.e., sGC and PDE-5. The results have primarily been obtained in animal models of liver cirrhosis. However, clinical and histochemical data suggest that the new biochemical model we propose can be applied to human liver cirrhosis. The role of PDE-5 as potential target for medical therapy of PH is discussed.

Activity within specific enteric neurochemical subtypes is correlated with distinct patterns of gastrointestinal motility in the murine colon

The enteric nervous system in the large intestine generates two important patterns relating to motility: 1) propagating rhythmic peristaltic smooth muscle contractions referred to as colonic migrating motor complexes (CMMCs) and 2) tonic inhibition, during which colonic smooth muscle contractions are suppressed. The precise neurobiological substrates underlying each of these patterns are unclear. Using transgenic animals expressing the genetically encoded calcium indicator GCaMP3 to monitor activity or the optogenetic actuator channelrhodopsin (ChR2) to drive activity in defined enteric neuronal subpopulations, we provide evidence that cholinergic and nitrergic neurons play significant roles in mediating CMMCs and tonic inhibition, respectively. Nitrergic neurons [neuronal nitric oxide synthase (nNOS)-positive neurons] expressing GCaMP3 exhibited higher levels of activity during periods of tonic inhibition than during CMMCs. Consistent with these findings, optogenetic activation of ChR2 in nitrergic neurons depressed ongoing CMMCs. Conversely, cholinergic neurons [choline acetyltransferase (ChAT)-positive neurons] expressing GCaMP3 markedly increased their activity during the CMMC. Treatment with the NO synthesis inhibitor Nω-nitro-l-arginine also augmented the activity of ChAT-GCaMP3 neurons, suggesting that the reciprocal patterns of activity exhibited by nitrergic and cholinergic enteric neurons during distinct phases of colonic motility may be related.NEW & NOTEWORTHY Correlating the activity of neuronal populations in the myenteric plexus to distinct periods of gastrointestinal motility is complicated by the difficulty of measuring the activity of specific neuronal subtypes. Here, using mice expressing genetically encoded calcium indicators or the optical actuator channelrhodopsin-2, we provide compelling evidence that cholinergic and nitrergic neurons play important roles in mediating coordinated propagating peristaltic contractions or tonic inhibition, respectively, in the murine colon.

Cell-specific effects of nitric oxide on the efficiency and frequency of long distance contractions in murine colon

BACKGROUND

Nitric oxide (NO) mediates inhibitory neurotransmission and is a critical component of neuronal programs that generate propulsive contractions. NO acts via its receptor NO-sensitive guanylyl cyclase (NO-GC) which is expressed in smooth muscle cells (SMC) and interstitial cells of Cajal (ICC). Organ bath studies with colonic rings from NO-GC knockout mice (GCKO) have indicated NO-GC to modulate spontaneous contractions. The cell-specific effects of NO-GC on the dominant pan-colonic propulsive contraction, the long distance contractions (LDCs), of whole colon preparations have not yet been described.

METHODS

Contractions of whole colon preparations from wild type (WT), global, and cell-specific GCKO were recorded. After transformation into spatiotemporal maps, motility patterns were analyzed. Simultaneous perfusion of the colon enabled the correlation of outflow with LDCs to analyze contraction efficiency.

KEY RESULTS

Deletion of NO-GC in both ICC and SMC (ie, in GCKO and SMC/ICC-GCKO) caused loss of typical LDC activity and instead generated high-frequency LDC-like contractions with inefficient propulsive activity. Frequency was also increased in WT, SMC-GCKO, and ICC-GCKO colon in the presence of L-NAME to block neuronal NO synthase. LDC efficiency was dependent on NO-GC in SMC as it was reduced in GCKO, SMC-GCKO, and ICC/SMC-GCKO colon; LDC efficiency was decreased in all genotypes in the presence of L-NAME.

CONCLUSIONS AND INFERENCES

NO/cGMP signaling is critical for normal peristaltic movements; as NO-GC in both SMC and ICC is essential, both cell types appear to work in synchrony. The efficiency of contractions to expel fluid is particularly influenced by NO-GC in SMC.

Differential sensitivity of gastric and small intestinal muscles to inducible knockdown of anoctamin 1 and the effects on gastrointestinal motility

KEY POINTS

Electrical pacemaking in gastrointestinal muscles is generated by specialized interstitial cells of Cajal that produce the patterns of contractions required for peristalsis and segmentation in the gut. The calcium-activated chloride conductance anoctamin-1 (Ano1) has been shown to be responsible for the generation of pacemaker activity in GI muscles, but this conclusion is established from studies of juvenile animals in which effects of reduced Ano1 on gastric emptying and motor patterns could not be evaluated. Knocking down Ano1 expression using Cre/LoxP technology caused dramatic changes in in gastric motor activity, with disrupted slow waves, abnormal phasic contractions and delayed gastric emptying; modest changes were noted in the small intestine. Comparison of the effects of Ano1 antagonists on muscles from juvenile and adult small intestinal muscles suggests that conductances in addition to Ano1 may develop with age and contribute to pacemaker activity.

ABSTRACT

Interstitial cells of Cajal (ICC) generate slow waves and transduce neurotransmitter signals in the gastrointestinal (GI) tract, facilitating normal motility patterns. ICC express a Ca2+ -activated Cl- conductance (CaCC), and constitutive knockout of the channel protein anoctamin-1 leads to loss of slow waves in gastric and intestinal muscles. These knockout experiments were performed on juvenile mice. However, additional experiments demonstrated significant differences in the sensitivity of gastric and intestinal muscles to antagonists of anoctamin-1 channels. Furthermore, the significance of anoctamin-1 and the electrical and mechanical behaviours facilitated by this conductance have not been evaluated on the motor behaviours of adult animals. Cre/loxP technology was used to generate cell-specific knockdowns of anoctamin-1 in ICC (KitCreERT2/+ ;Ano1tm2jrr/+ ) in GI muscles. The recombination efficiency of KitCreERT was evaluated with an eGFP reporter, molecular techniques and immunohistochemistry. Electrical and contractile experiments were used to examine the consequences of anoctamin-1 knockdown on pacemaker activity, mechanical responses, gastric motility patterns, gastric emptying and GI transit. Reduced anoctamin-1 caused loss of gastric, but not intestinal slow waves. Irregular spike complexes developed in gastric muscles, leading to uncoordinated antral contractions, delayed gastric emptying and increased total GI transit time. Slow waves in intestinal muscles of juvenile mice were more sensitive to anoctamin-1 antagonists than slow waves in adult muscles. The low susceptibility to anoctamin-1 knockdown and weak efficacy of anoctamin-1 antagonists in inhibiting slow waves in adult small intestinal muscles suggest that a conductance in addition to anoctamin-1 may develop in small intestinal ICC with ageing and contribute to pacemaker activity.

Tonic inhibition of murine proximal colon is due to nitrergic suppression of Ca2+ signaling in interstitial cells of Cajal

Spontaneous excitability and contractions of colonic smooth muscle cells (SMCs) are normally suppressed by inputs from inhibitory motor neurons, a behavior known as tonic inhibition. The post-junctional cell(s) mediating tonic inhibition have not been elucidated. We investigated the post-junctional cells mediating tonic inhibition in the proximal colon and whether tonic inhibition results from suppression of the activity of Ano1 channels, which are expressed exclusively in interstitial cells of Cajal (ICC). We found that tetrodotoxin (TTX), an inhibitor of nitric oxide (NO) synthesis, L-NNA, and an inhibitor of soluble guanylyl cyclase, ODQ, greatly enhanced colonic contractions. Ano1 antagonists, benzbromarone and Ani9 inhibited the effects of TTX, L-NNA and ODQ. Ano1 channels are activated by Ca²⁺ release from the endoplasmic reticulum (ER) in ICC, and blocking Ca²⁺ release with a SERCA inhibitor (thapsigargin) or a store-operated Ca²⁺ entry blocker (GSK 7975 A) reversed the effects of TTX, L-NNA and ODQ. Ca²⁺ imaging revealed that TTX, L-NNA and ODQ increased Ca²⁺ transient firing in colonic ICC. Our results suggest that tonic inhibition in the proximal colon occurs through suppression of Ca²⁺ release events in ICC. Suppression of Ca²⁺ release in ICC limits the open probability of Ano1 channels, reducing the excitability of electrically-coupled SMCs.

Nitric oxide and its role as a non-adrenergic, non-cholinergic inhibitory neurotransmitter in the gastrointestinal tract

NO is a neurotransmitter released from enteric inhibitory neurons and responsible for modulating gastrointestinal (GI) motor behaviour. Enteric neurons express nNOS (NOS1) that associates with membranes of nerve varicosities. NO released from neurons binds to soluble guanylate cyclase in post-junctional cells to generate cGMP. cGMP-dependent protein kinase type 1 (PKG1) is a major mediator but perhaps not the only pathway involved in cGMP-mediated effects in GI muscles based on gene deletion studies. NOS1+ neurons form close contacts with smooth muscle cells (SMCs), interstitial cells of Cajal (ICC) and PDGFRα+ cells, and these cells are electrically coupled (SIP syncytium). Cell-specific gene deletion studies have shown that nitrergic responses are due to mechanisms in SMCs and ICC. Controversy exists about the ion channels and other post-junctional mechanisms that mediate nitrergic responses in GI muscles. Reduced nNOS expression in enteric inhibitory motor neurons and/or reduced connectivity between nNOS+ neurons and the SIP syncytium appear to be responsible for motor defects that develop in diabetes. An overproduction of NO in some inflammatory conditions also impairs normal GI motor activity. This review summarizes recent findings regarding the role of NO as an enteric inhibitory neurotransmitter. LINKED ARTICLES: This article is part of a themed section on Nitric Oxide 20 Years from the 1998 Nobel Prize. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.2/issuetoc.

Effects of Fengliao-Changweikang in Diarrhea-predominant Irritable Bowel Syndrome Rats and Its Mechanism Involving Colonic Motility

Background/Aims

This study was designed to investigate the effect of Fengliao-Changweikang (FLCWK) in diarrhea-predominant irritable bowel syndrome (IBS-D) rats and explore its underlying mechanisms.

Methods

IBS-D model rats were induced by neonatal maternal separation (NMS) combined with restraint stress (RS). In in vivo experiments, the model rats were randomly divided into 5 groups: NMS + RS, FLCWK (low dose, middle dose, and high dose), and pinaverium bromide. The normal control (no handling) rats were classified as the NH group. The therapeutic effect of FLCWK was evaluated by fecal characteristics, electromyographic response and abdominal withdrawal reflex scores. In in vitro experiments, the model rats were randomly divided into 2 groups: NMS + RS, FLCWK (middle dose), and no handling rats were used as the NH group. The differences in basic tension and ACh-induced tension of isolated colonic longitudinal smooth muscle strips (CLSMs) among the 3 groups were observed. In addition, different inhibitors (nifedipine, TMB-8, L-NAME, methylene blue, and 4-AP) were pretreated to explore the underlying mechanisms.

Results

In in vivo experiments, fecal characteristics, electromyographic response, and abdominal withdrawal reflex scores significantly improved in the FLCWK group, compared with the NMS + RS group. In in vitro experiments, the basic tension and ACh-induced tension of CLSMs in IBS-D rats were significantly inhibited by FLCWK. After pre-treatment with different inhibitors, the ACh-induced tension of CLSMs in each group showed no significant difference.

Conclusions

FLCWK manifested curative effect in IBS-D rats by inhibiting colonic contraction. The underlying mechanisms may be related to regulatory pathway of nitric oxide/cGMP/Ca²⁺ and specific potassium channels.

Nitrergic signaling via interstitial cells of Cajal and smooth muscle cells influences circular smooth muscle contractility in murine colon

BACKGROUND

Regulation of gastrointestinal motility involves excitatory and inhibitory neurotransmission. Nitric oxide (NO), the major inhibitory neurotransmitter, acts via its receptor NO-sensitive guanylyl cyclase (NO-GC). In the GI tract, NO-GC is expressed in several cell types such as smooth muscle cells (SMC) and interstitial cells of Cajal (ICC). Using cell-specific knockout mice, we have previously shown that NO-GC modulates spontaneous contractions in colonic longitudinal smooth muscle. However, its detailed role in the colonic circular smooth muscle is still unclear.

METHODS

Myography was performed to evaluate spontaneous contractions in rings of proximal colon (2.5 mm) from global (GCKO) and cell-specific knockout mice for NO-GC. Immunohistochemistry and in situ hybridization were used to specify NO-GC expression.

KEY RESULTS

Colonic circular smooth muscle showed three different contraction patterns: high-frequency ripples, slow phasic contractions, and large contractions. Ripples formed independently of NO-GC. Slow phasic contractions occurred intermittently in WT, SMC-GCKO, and ICC-GCKO tissue, whereas they were more prominent and prolonged in GCKO and SMC/ICC-GCKO tissue. Tetrodotoxin and the NO-GC inhibitor ODQ transformed slow phasic contractions of WT and single cell-specific knockout into GCKO-like contractions. ODQ increased the frequency of large contractions in WT and ICC-GCKO colon but not in GCKO, SMC-GCKO, and SMC/ICC-GCKO preparations. Tetrodotoxin and hexamethonium abolished large contractions.

CONCLUSIONS AND INFERENCES

We conclude that short rings of murine colon can be effectively used to record spontaneous contractions. Although NO-GC in SMC determines smooth muscle tone, concerted action of NO-GC in both SMC and ICC modulates slow phasic contractions and large contractions.

Comparison of nitrergic signaling in circular and longitudinal smooth muscle of murine ileum

BACKGROUND

Gastrointestinal (GI) motility originates from coordinated movements of circular (CM) and longitudinal (LM) smooth muscle. How the two muscle layers react individually to nitrergic input and how they integrate nitrergic signaling is not thoroughly understood.

METHODS

We used immunohistochemistry to unveil expression of NO-sensitive guanylyl cyclase (NO-GC) in the ileum. For functional analyses, we measured tone of ileal CM and spontaneous contractions in both ileal muscle layers from mice lacking NO-GC globally (GCKO) and specifically in smooth muscle cells (SMC-GCKO).

KEY RESULTS

In contrast to other parts of the GI tract, NO-GC was not expressed in ckit-positive cells in ileum. NO-GC expression was intense in platelet-derived growth factor receptor α-positive cells and in yet unidentified cells of myenteric plexus and serosa. Both CM and LM developed spontaneous contractile activity; frequency and duration of their spontaneous contractions were identical. The amplitude of spontaneous contractions in CM was increased in the absence of NO-GC. In ileum from control (ctrl) animals, inhibition of NO-GC increased whereas NO-GC stimulation decreased tissue tone. In contrast, contractile activity in LM was not different between ctrl and knockout strains. Here, NO led to suppression of spontaneous contractions of ctrl ileum whereas GCKO tissue was unaffected. To our surprise, NO suppressed spontaneous contractions in SMC-GCKO ileum indicating participation of other cell type(s).

CONCLUSIONS AND INFERENCES

NO-GC in SMC is involved in the regulation of tone and amplitude of spontaneous contractions in ileal CM. In LM, NO induces suppression of spontaneous contractions via NO-GC in a non-SMC type.

The IgCAM CLMP regulates expression of Connexin43 and Connexin45 in intestinal and ureteral smooth muscle contraction in mice

CAR-like membrane protein (CLMP), an immunoglobulin cell adhesion molecule (IgCAM), has been implicated in congenital short-bowel syndrome in humans, a condition with high mortality for which there is currently no cure. We therefore studied the function of CLMP in a Clmp-deficient mouse model. Although we found that the levels of mRNAs encoding Connexin43 or Connexin45 were not or were only marginally affected, respectively, by Clmp deficiency, the absence of CLMP caused a severe reduction of both proteins in smooth muscle cells of the intestine and of Connexin43 in the ureter. Analysis of calcium signaling revealed a disordered cell-cell communication between smooth muscle cells, which in turn induced an impaired and uncoordinated motility of the intestine and the ureter. Consequently, insufficient transport of chyme and urine caused a fatal delay to thrive, a high rate of mortality, and provoked a severe hydronephrosis in CLMP knockouts. Neurotransmission and the capability of smooth muscle cells to contract in ring preparations of the intestine were not altered. Physical obstructions were not detectable and an overall normal histology in the intestine as well as in the ureter was observed, except for a slight hypertrophy of smooth muscle layers. Deletion of Clmp did not lead to a reduced length of the intestine as shown for the human CLMP gene but resulted in gut malrotations. In sum, the absence of CLMP caused functional obstructions in the intestinal tract and ureter by impaired peristaltic contractions most likely due to a lack of gap-junctional communication between smooth muscle cells.

Summary: The function of the immunoglobulin cell adhesion molecule CLMP was investigated in a mouse model. CLMP is essential for intestinal and ureteral peristalsis, and for expression of Connexin43 and 45 in smooth muscle cells.

Treatment with low doses of aspirin during chronic phase of experimental Chagas' disease increases oesophageal nitrergic neuronal subpopulation in mice

Patients with Chagas' disease may develop dysfunctions of oesophageal and colonic motility resulting from the degeneration or loss of the myenteric neurons of the enteric nervous system. Studies have shown that the use of aspirin, also known as acetylsalicylic acid (ASA), influences the pathogenesis of the disease. However, this remains controversial. The aim of this study was to evaluate the consequences of treatment with low doses of aspirin during the chronic phase of Chagas' disease on oesophageal function. Twenty male Swiss mice, 60 days of age, were used. The animals were infected with Y strain of Trypanosoma cruzi, injected intraperitoneally. Aspirin was given at a dose of 50 mg/kg to some of the infected animals, from the 55th to 63rd day after inoculation on consecutive days, and from the 65th to 75th day on alternate days. We investigated food passage of time, wall structure and nitrergic neuronal population of the distal oesophagus. Our data revealed that the use of low doses of aspirin in chronic Chagas' disease caused an increase in the number of nitrergic neurons and partially prevented hypertrophy of the oesophagus. In addition, the aspirin administration impeded Chagas' diseases associated changes in intestinal transit time. Thus treatment with aspirin in the chronic phase of Chagas' disease changes the natural history of the disease and raises the possibility of using it as a new therapeutic approach to the treatment of this aspect of Chagas' disease pathology.

Changes in the interstitial cells of Cajal and neuronal nitric oxide synthase positive neuronal cells with aging in the esophagus of F344 rats

The aging-associated cellular and molecular changes in esophagus have not been established, yet. Thus we evaluated histological structure, interstitial cells of Cajal (ICCs), neuronal nitric oxide synthase (nNOS)-positive cells, and contractility in the esophagus of Fischer 344 rat at different ages (6-, 31-, 74-weeks, and 2-years). The lamina propria thickness and endomysial area were calculated. The immunoreactivity of c-Kit, nNOS and protein gene product (PGP) 9.5 was counted after immunohistochemistry. Expression of c-Kit, stem cell factor (SCF), nNOS and PGP 9.5 mRNA was measured by real-time PCR, and expression of c-Kit and nNOS protein was detected by Western blot. Isovolumetric contractile force measurement and electrical field stimulation (EFS) were conducted. The lamina propria thickness increased (6 week vs 2 year, P = 0.005) and the endomysial area of longitudinal muscle decreased with aging (6 week vs 2 year, P<0.001), while endomysial area of circular muscle did not significantly decrease. The proportions of NOS-immunoreactive cells and c-Kit-immunoreactive areas declined with aging (6 week vs 2 year; P<0.001 and P = 0.004, respectively), but there was no significant change of PGP 9.5-immunopositiviy. The expressions of nNOS, c-Kit and SCF mRNA also reduced with aging (6 week vs 2 year; P = 0.006, P = 0.001 and P = 0.006, respectively), while the change of PGP 9.5 mRNA expression was not significant. Western blot showed the significant decreases of nNOS and c-Kit protein expression with aging (6 week vs 2 year; P = 0.008 and P = 0.012, respectively). The EFS-induced esophageal contractions significantly decreased in 2-yr-old rat compared with 6-wk-old rats, however, L-NG-Nitroarginine methylester did not significantly increase the spontaneous and EFS-induced contractions in the 6-wk- and 2-yr-old rat esophagus. In conclusion, an increase of lamina propria thickness, a decrease of endomysial area, c-Kit, SCF and NOS expression with preserved total enteric neurons, and contractility in aged rat esophagus may explain the aging-associated esophageal dysmotility.

Inhibitory action of oxytocin on spontaneous contraction of rat distal colon by nitrergic mechanism: involvement of cyclic GMP and apamin-sensitive K+ channels

AIM

The mechanisms underlying the inhibitory effects of oxytocin (OT) on colon tone are not totally understood. We explore the mechanisms of OT on spontaneous contractility in rat distal colon and identify the mediators involved in this action.

METHODS

In rat distal colon strips, mechanical activity was analysed and the production of nitric oxide (NO) in tissue loaded with the fluorochrome DAF-FM was visualized by confocal microscopy. OT receptor (OTR) expression was determined by Western blotting and immunofluorescence.

RESULTS

In rat distal colon, OT produced a concentration-dependent reduction in the spontaneous contraction, which was abolished by the OTR antagonist atosiban, the neural blocker tetrodotoxin and the inhibitor of neuronal nitric oxide synthase (nNOS) NPLA. The inhibitory effects of OT were not affected by propranolol, atropine, the nicotinic cholinoceptor blocker hexamethonium, the vasoactive intestinal peptide receptor antagonist VIPHyb, the P₂ purinoceptor antagonist PPADS, the adenosine A1 receptors antagonist DPCPX and the prostacyclin receptor antagonist Ro1138452. The soluble guanylyl cyclase (sGC) inhibitor ODQ and the small conductance Ca²⁺ -activated K⁺ (_Ca K⁺ ) channels blocker apamin significantly reduced the relaxation induced by OT, nicotine, sodium nitroprusside and the sGC activator BAY 41-2272. The neural release of NO elicited by OT was prevented by NPLA, tetrodotoxin and atosiban. The presence of the OTR and its co-localization with nNOS was detected by immunohistochemistry and Western blotting experiments.

CONCLUSION

These results demonstrate the NO release from enteric neurones induced by activation of OTR mediates distal colon relaxation. sGC and small conductance _Ca K⁺ channels are involved in this relaxation.

The Mystery of the Interstitial Cells in the Urinary Bladder

Intrinsic mechanisms to restrain smooth muscle excitability are present in the bladder, and premature contractions during filling indicate a pathological phenotype. Some investigators have proposed that c-Kit⁺ interstitial cells (ICs) are pacemakers and intermediaries in efferent and afferent neural activity, but recent findings suggest these cells have been misidentified and their functions have been misinterpreted. Cells reported to be c-Kit⁺ cells colabel with vimentin antibodies, but vimentin is not a specific marker for c-Kit⁺ cells. A recent report shows that c-Kit⁺ cells in several species coexpress mast cell tryptase, suggesting that they are likely to be mast cells. In fact, most bladder ICs labeled with vimentin antibodies coexpress platelet-derived growth factor receptor α (PDGFRα). Rather than an excitatory phenotype, PDGFRα⁺ cells convey inhibitory regulation in the detrusor, and inhibitory mechanisms are activated by purines and stretch. PDGFRα⁺ cells restrain premature development of contractions during bladder filling, and overactive behavior develops when the inhibitory pathways in these cells are blocked. PDGFRα⁺ cells are also a prominent cell type in the submucosa and lamina propria, but little is known about their function in these locations. Effective pharmacological manipulation of bladder ICs depends on proper identification and further study of the pathways in these cells that affect bladder functions.

The nitric oxide synthase 2 pathway is targeted by both pro- and anti-inflammatory treatments in the immature human intestine

BACKGROUND AND AIM

NO synthase 2 (NOS2) was recently identified as one the most overexpressed genes in intestinal samples of premature infants with necrotizing enterocolitis (NEC). NOS2 is widely implicated in the processes of epithelial cell injury/apoptosis and host immune defense but its specific role in inflammation of the immature human intestinal mucosa remains unclear. Interestingly, factors that prevent NEC such as epidermal growth factor (EGF) attenuate the inflammatory response in the mid-gestation human small intestine using serum-free organ culture while drugs that are associated with NEC occurrence such as the non-steroidal anti-inflammatory drug, indomethacin (INDO), exert multiple detrimental effects on the immature human intestine. In this study we investigate the potential role of NOS2 in modulating the gut inflammatory response under protective and stressful conditions by determining the expression profile of NOS2 and its downstream pathways in the immature intestine.

METHODS

Gene expression profiles of cultured mid-gestation human intestinal explants were investigated in the absence or presence of a physiological concentration of EGF (50 ng/ml) or 1 μM INDO for 48 h using Illumina whole genome microarrays, Ingenuity Pathway Analysis software and quantitative PCR to investigate the expression of NOS2 and NOS2-pathway related genes.

RESULTS

In the immature intestine, NOS2 expression was found to be increased by EGF and repressed by INDO. Bioinformatic analysis identified differentially regulated pathways where NOS2 is known to play an important role including citrulline/arginine metabolism, epithelial cell junctions and oxidative stress. At the individual gene level, we identified many differentially expressed genes of the citrulline/arginine metabolism pathway such as ARG1, ARG2, GLS, OAT and OTC in response to EGF and INDO. Gene expression of tight junction components such as CLDN1, CLDN2, CLDN7 and OCN and of antioxidant markers such as DUOX2, GPX2, SOD2 were also found to be differentially modulated by EGF and INDO.

CONCLUSION

These results suggest that the protective effect of EGF and the deleterious influence of INDO on the immature intestine could be mediated via regulation of NOS2. Pathways downstream of NOS2 involved with these effects include metabolism linked to NO production, epithelial barrier permeability and antioxidant expression. These results suggest that NOS2 is a likely regulator of the inflammatory response in the immature human gut and may provide a mechanistic basis for the protective effect of EGF and the deleterious effects of INDO.

Change in the Interstitial Cells of Cajal and nNOS Positive Neuronal Cells with Aging in the Stomach of F344 Rats

The gastric accommodation reflex is an important mechanism in gastric physiology. However, the aging-associated structural and functional changes in gastric relaxation have not yet been established. Thus, we evaluated the molecular changes of interstitial cell of Cajal (ICC) and neuronal nitric oxide synthase (nNOS) and the function changes in the corpus of F344 rats at different ages (6-, 31-, 74-wk and 2-yr). The proportion of the c-Kit-positive area in the submucosal border (SMB) and myenteric plexus (MP) layer was significantly lower in the older rats, as indicated by immunohistochemistry. The density of the nNOS-positive immunoreactive area also decreased with age in the SMB, circular muscle (CM), and MP. Similarly, the percent of nNOS-positive neuronal cells per total neuronal cells and the proportion of nNOS immunoreactive area of MP also decreased in aged rats. In addition, the mRNA and protein expression of c-Kit and nNOS significantly decreased with age. Expression of stem cell factor (SCF) and the pan-neuronal marker PGP 9.5 mRNA was significantly lower in the older rats than in the younger rats. Barostat studies showed no difference depending on age. Instead, the change of volume was significantly decreased by L-NG63-nitroarginine methyl ester in the 2-yr-old rats compared with the 6-wk-old rats (P = 0.003). Taken together, the quantitative and molecular nNOS changes in the stomach might play a role in the decrease of gastric accommodation with age.

cGMP becomes a drug target

Cyclic guanosine 3′,5′-monophosphate (cGMP) serves as a second messenger molecule, which regulates pleiotropic cellular functions in health and disease. cGMP is generated by particulate or soluble guanylyl cyclases upon stimulation with natriuretic peptides or nitric oxide, respectively. Furthermore, the cGMP concentration is modulated by cGMP-degrading phosphodiesterases. Several targets of cGMP are utilized to effect its various cellular functions. These effector molecules comprise cGMP-dependent protein kinases, ion channels, and phosphodiesterases. During the last decade, it emerged that cGMP is a novel drug target for the treatment of pulmonary and cardiovascular disorders. In this respect, several drugs were developed, which are now in clinical phase studies for, e.g., pulmonary hypertension or cardiovascular diseases. These new drugs act NO-independently with/without heme on soluble guanylyl cyclases or induce subtypes of particular guanylyl cyclases and thereby lead to new therapeutic concepts and horizons. In this regard, the fifth cGMP meeting held in June 2011 in Halle, Germany, comprised the new therapeutic challenges with the novel functional and structural concepts of cGMP generating and effector molecules. This report summarizes the new data on molecular mechanisms, (patho)physiological relevance, and therapeutic potentials of the cGMP signaling system that were presented at this meeting.

Enteric Inhibitory Neurotransmission, Starting Down Under

The idea of an inhibitory innervation in the gut came from Geoff Burnstock's group at the University of Melbourne in the 1960s. Being resistant to antagonists of norepinephrine and acetylcholine, enteric inhibitory neurotransmission became known as non-cholinergic, non-adrenergic (NANC) neurotransmission. ATP (or a closely related nucleotide) was proposed as the inhibitory neurotransmitter based on release of purines during nerve stimulation and similarities between responses to ATP and transmural nerve stimulation in several gut preparations. Apamin was found to block purinergic responses, providing evidence that small-conductance Ca(2+)-activated K(+) (SK) channels were responsible for inhibitory junction potentials (IJPs). Actually the IJPs in GI muscles are composed of multiple components, and later studies discovered nitric oxide (NO) to be the other major mediator of NANC inhibitory neurotransmission. The purinergic component of enteric inhibitory neurotransmission is mediated by P2Y1 receptors, and this component is absent in P2Y1(-/-) mice. The criteria for a neurotransmitter are better met by β-nicotinamide adenine dinucleotide (β-NAD) or its immediate metabolite ADP-ribose (ADPR) than by ATP. The cells mediating post-junctional responses have been identified. In addition to smooth muscle cells, two classes of interstitial cells express receptors and effectors for NANC neurotransmitters and are electrically coupled to smooth muscle cells. This integrated structure has been named the SIP syncytium. Interstitial cells of Cajal are involved in transduction of cholinergic and nitrergic inputs to GI muscles, and PDGFRα(+) cells mediate purinergic effects. This short symposium report summarizes major historical points of interest and some of the more recent findings related to enteric inhibitory neurotransmission.

Nitrergic signalling via interstitial cells of Cajal regulates motor activity in murine colon

In the enteric nervous systems, NO is released from nitrergic neurons as a major inhibitory neurotransmitter. NO acts via NO-sensitive guanylyl cyclase (NO-GC), which is found in different gastrointestinal (GI) cell types including smooth muscle cells (SMCs) and interstitial cells of Cajal (ICC). The precise mechanism of nitrergic signalling through these two cell types to regulate colonic spontaneous contractions is not fully understood yet. In the present study we investigated the impact of endogenous and exogenous NO on colonic contractile motor activity using mice lacking nitric oxide-sensitive guanylyl cyclase (NO-GC) globally and specifically in SMCs and ICC. Longitudinal smooth muscle of proximal colon from wild-type (WT) and knockout (KO) mouse strains exhibited spontaneous contractile activity ex vivo. WT and smooth muscle-specific guanylyl cyclase knockout (SMC-GCKO) colon showed an arrhythmic contractile activity with varying amplitudes and frequencies. In contrast, colon from global and ICC-specific guanylyl cyclase knockout (ICC-GCKO) animals showed a regular contractile rhythm with constant duration and amplitude of the rhythmic contractions. Nerve blockade (tetrodotoxin) or specific blockade of NO signalling (L-NAME, ODQ) did not significantly affect contractions of GCKO and ICC-GCKO colon whereas the arrhythmic contractile patterns of WT and SMC-GCKO colon were transformed into uniform motor patterns. In contrast, the response to electric field-stimulated neuronal NO release was similar in SMC-GCKO and global GCKO. In conclusion, our results indicate that basal enteric NO release acts via myenteric ICC to influence the generation of spontaneous contractions whereas the effects of elevated endogenous NO are mediated by SMCs in the murine proximal colon.

Dominant role of interstitial cells of Cajal in nitrergic relaxation of murine lower oesophageal sphincter

Oesophageal achalasia is a disease known to result from reduced relaxation of the lower oesophageal sphincter (LES). Nitric oxide (NO) is one of the main inhibitory transmitters. NO-sensitive guanylyl cyclase (NO-GC) acts as the key target of NO and, by the generation of cGMP, mediates nitrergic relaxation in the LES. To date, the exact mechanism of nitrergic LES relaxation is still insufficiently elucidated. To clarify the role of NO-GC in LES relaxation, we used cell-specific knockout (KO) mouse lines for NO-GC. These include mice lacking NO-GC in smooth muscle cells (SMC-GCKO), in interstitial cells of Cajal (ICC-GCKO) and in both SMC/ICC (SMC/ICC-GCKO). We applied oesophageal manometry to study the functionality of LES in vivo. Isometric force studies were performed to monitor LES responsiveness to exogenous NO and electric field stimulation of intrinsic nerves in vitro. Cell-specific expression/deletion of NO-GC was monitored by immunohistochemistry. Swallowing-induced LES relaxation is strongly reduced by deletion of NO-GC in ICC. Basal LES tone is affected by NO-GC deletion in either SMC or ICC. Lack of NO-GC in both cells leads to a complete interruption of NO-induced relaxation and, therefore, to an achalasia-like phenotype similar to that seen in global GCKO mice. Our data indicate that regulation of basal LES tone is based on a dual mechanism mediated by NO-GC in SMC and ICC whereas swallow-induced LES relaxation is mainly regulated by nitrergic mechanisms in ICC.

Differential functional role of purinergic and nitrergic inhibitory cotransmitters in human colonic relaxation

AIM

ATP and nitric oxide (NO) are released from enteric inhibitory motor neurones and are responsible for colonic smooth muscle relaxation. However, how frequency of neural stimulation affects this cotransmission process and the post-junctional responses has not been systematically characterized in the human colon.

METHODS

The dynamics of inhibitory cotransmission were studied using different protocols of electrical field stimulation (EFS) to characterize the inhibitory junction potentials (IJP) and the corresponding relaxation in colonic strips obtained from 36 patients.

RESULTS

Single pulses elicited a fast IJP (IJPf(MAX) = -27.6 ± 1.6 mV), sensitive to the P2Y1 antagonist MRS2500 1 μm, that ran down with frequency increase leaving a residual hyperpolarization at high frequencies (IJPf∞ = -3.7 ± 0.6 mV). Accordingly, low frequencies of EFS caused purinergic transient relaxations that cannot be maintained at high frequencies. Addition of the P2Y1 agonist MRS2365 10 μm during the purinergic rundown did not cause any hyperpolarization. Protein kinase C (PKC), a putative P2Y1 desensitizator, was able to reduce the amplitude of the IJPf when activated, but the rundown was not modified by PKC inhibitors. Frequencies higher than 0.60 ± 0.15 Hz were needed to evoke a sustained nitrergic hyperpolarization that progressively increased reaching IJPs∞ = -13 ± 0.4 mV at high frequencies and leading to a sustained inhibition of spontaneous motility.

CONCLUSION

Changes in frequency of stimulation possibly mimicking neuronal firing will post-junctionally determine purinergic vs. nitrergic responses underlying different functional roles. NO will be responsible for sustained relaxations needed in physiological processes such as storage, while purinergic neurotransmission evoking sharp transient relaxations will be dominant in processes such as propulsion.

Nitrergic neuromuscular transmission in the mouse internal anal sphincter is accomplished by multiple pathways and postjunctional effector cells

The effector cells and second messengers participating in nitrergic neuromuscular transmission (NMT) were investigated in the mouse internal anal sphincter (IAS). Protein expression of guanylate cyclase (GCα, GCβ) and cyclic GMP-dependent protein kinase I (cGKI) were examined in cryostat sections with dual-labeling immunohistochemical techniques in PDGFRα(+) cells, interstitial cells of Cajal (ICC), and smooth muscle cells (SMC). Gene expression levels were determined with quantitative PCR of dispersed cells from Pdgfrα(egfp/+), Kit(copGFP/+), and smMHC(Cre-egfp) mice sorted with FACS. The relative gene and protein expression levels of GCα and GCβ were PDGFRα(+) cells > ICC ≫ SMC. In contrast, cGKI gene expression sequence was SMC = ICC > PDGFRα(+) cells whereas cGKI protein expression sequence was neurons > SMC ≫ ICC = PDGFRα(+) cells. The functional role of cGKI was investigated in cGKI(-/-) mice. Relaxation with 8-bromo (8-Br)-cGMP was greatly reduced in cGKI(-/-) mice whereas responses to sodium nitroprusside (SNP) were partially reduced and forskolin responses were unchanged. A nitrergic relaxation occurred with nerve stimulation (NS, 5 Hz, 60 s) in cGKI(+/+) and cGKI(-/-) mice although there was a small reduction in the cGKI(-/-) mouse. N(ω)-nitro-l-arginine (l-NNA) abolished responses during the first 20-30 s of NS in both animals. The GC inhibitor ODQ greatly reduced or abolished SNP and nitrergic NS responses in both animals. These data confirm an essential role for GC in NO-induced relaxation in the IAS. However, the expression of GC and cGKI by all three cell types suggests that each may participate in coordinating muscular responses to NO. The persistence of nitrergic NMT in the cGKI(-/-) mouse suggests the presence of a significant GC-dependent, cGKI-independent pathway.

Lack of effect of ODQ does not exclude cGMP signalling via NO-sensitive guanylyl cyclase

BACKGROUND AND PURPOSE

Nitric oxide (NO) is known to activate NO-sensitive guanylyl cyclase (NO-GC) and to elicit cGMP production. However, NO has also been proposed to induce cGMP-independent effects. It is accepted practice to use specific NO-GC inhibitors, such as ODQ or NS2028, to assess cGMP-dependent NO effects. Consequently, NO-induced reactions seen in the presence of these inhibitors commonly serve as an affirmation of cGMP independence.

EXPERIMENTAL APPROACH

We evaluated the use of ODQ to discriminate between cGMP-dependent and cGMP-independent NO effects. NO-GC-expressing HEK cells, platelets and tissues from wild type (WT) and NO-GC-deficient mice (GCKO) were used.

KEY RESULTS

NO donors led to accumulation of cGMP in platelets and GC-expressing HEK cells and induced phosphorylation of the vasodilator-stimulated phosphoprotein in platelets; both effects were reduced by ODQ. High concentrations of NO donors, however, overrode the inhibitory effect of ODQ. Correspondingly, ODQ inhibited but did not fully eliminate NO-induced relaxation of aorta and fundus from WT mice. Relaxation induced by endogenously released NO was fully or partially inhibited by ODQ in fundus and aorta, respectively. In aorta and fundus of GCKO mice NO-induced relaxation was absent and served as standard for complete NO-GC inhibition.

CONCLUSIONS AND IMPLICATIONS

High NO concentrations can overcome the inhibitory effect of ODQ on NO-GC. Smooth muscle relaxation induced by NO donors/endogenously released NO in the presence of ODQ in WT was absent in GCKO animals indicating involvement of NO-GC. Accordingly, NO-induced effects in the presence of ODQ do not necessarily prove cGMP independence.

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.

Interstitial cells of Cajal: update on basic and clinical science

The basic science and clinical interest in the networks of interstitial cells of Cajal (ICC) keep growing, and here, research from 2010 to mid-2013 is highlighted. High-resolution gastrointestinal manometry and spatiotemporal mapping are bringing exciting new insights into motor patterns, their function and their myogenic and neurogenic origins, as well as the role of ICC. Critically important knowledge is emerging on the partaking of PDGFRα+ cells in ICC pacemaker networks. Evidence is emerging that ICC and PDGFRα+ cells have unique direct roles in muscle innervation. Chronic constipation is associated with loss and injury to ICC, which is stimulating extensive research into maintenance and repair of ICC after injury. In gastroparesis, high-resolution electrical and mechanical studies are beginning to elucidate the pathophysiological role of ICC and the pacemaker system in this condition. Receptors and ion channels that play a role in ICC function are being discovered and characterized, which paves the way for pharmacological interventions in gut motility disorders through ICC.

The significance of interstitial cells in neurogastroenterology

Smooth muscle layers of the gastrointestinal tract consist of a heterogeneous population of cells that include enteric neurons, several classes of interstitial cells of mesenchymal origin, a variety of immune cells and smooth muscle cells (SMCs). Over the last number of years the complexity of the interactions between these cell types has begun to emerge. For example, interstitial cells, consisting of both interstitial cells of Cajal (ICC) and platelet-derived growth factor receptor alpha-positive (PDGFRα(+)) cells generate pacemaker activity throughout the gastrointestinal (GI) tract and also transduce enteric motor nerve signals and mechanosensitivity to adjacent SMCs. ICC and PDGFRα(+) cells are electrically coupled to SMCs possibly via gap junctions forming a multicellular functional syncytium termed the SIP syncytium. Cells that make up the SIP syncytium are highly specialized containing unique receptors, ion channels and intracellular signaling pathways that regulate the excitability of GI muscles. The unique role of these cells in coordinating GI motility is evident by the altered motility patterns in animal models where interstitial cell networks are disrupted. Although considerable advances have been made in recent years on our understanding of the roles of these cells within the SIP syncytium, the full physiological functions of these cells and the consequences of their disruption in GI muscles have not been clearly defined. This review gives a synopsis of the history of interstitial cell discovery and highlights recent advances in structural, molecular expression and functional roles of these cells in the GI tract.

The significance of interstitial cells in neurogastroenterology

Smooth muscle layers of the gastrointestinal tract consist of a heterogeneous population of cells that include enteric neurons, several classes of interstitial cells of mesenchymal origin, a variety of immune cells and smooth muscle cells (SMCs). Over the last number of years the complexity of the interactions between these cell types has begun to emerge. For example, interstitial cells, consisting of both interstitial cells of Cajal (ICC) and platelet-derived growth factor receptor alpha-positive (PDGFRα(+)) cells generate pacemaker activity throughout the gastrointestinal (GI) tract and also transduce enteric motor nerve signals and mechanosensitivity to adjacent SMCs. ICC and PDGFRα(+) cells are electrically coupled to SMCs possibly via gap junctions forming a multicellular functional syncytium termed the SIP syncytium. Cells that make up the SIP syncytium are highly specialized containing unique receptors, ion channels and intracellular signaling pathways that regulate the excitability of GI muscles. The unique role of these cells in coordinating GI motility is evident by the altered motility patterns in animal models where interstitial cell networks are disrupted. Although considerable advances have been made in recent years on our understanding of the roles of these cells within the SIP syncytium, the full physiological functions of these cells and the consequences of their disruption in GI muscles have not been clearly defined. This review gives a synopsis of the history of interstitial cell discovery and highlights recent advances in structural, molecular expression and functional roles of these cells in the GI tract.

Interstitial cells of Cajal mediate nitrergic inhibitory neurotransmission in the murine gastrointestinal tract

Nitric oxide (NO) is a major inhibitory neurotransmitter in the gastrointestinal (GI) tract. Its main effector, NO-sensitive guanylyl cyclase (NO-GC), is expressed in several GI cell types, including smooth muscle cells (SMC), interstitial cells of Cajal (ICC), and fibroblast-like cells. Up to date, the interplay between neurons and these cells to initiate a nitrergic inhibitory junction potential (IJP) is unclear. Here, we investigate the origin of the nitrergic IJP in murine fundus and colon. IJPs were determined in fundus and colon SMC of mice lacking NO-GC globally (GCKO) and specifically in SMC (SM-GCKO), ICC (ICC-GCKO), and both SMC/ICC (SM/ICC-GCKO). Nitrergic IJP was abolished in ICC-GCKO fundus and reduced in SM-GCKO fundus. In the colon, the amplitude of nitrergic IJP was reduced in ICC-GCKO, whereas nitrergic IJP in SM-GCKO was reduced in duration. These results were corroborated by loss of the nitrergic IJP in global GCKO. In conclusion, our results prove the obligatory role of NO-GC in ICC for the initiation of an IJP. NO-GC in SMC appears to enhance the nitrergic IJP, resulting in a stronger and prolonged hyperpolarization in fundus and colon SMC, respectively. Thus NO-GC in both cell types is mandatory to induce a full nitrergic IJP. Our data from the colon clearly reveal the nitrergic IJP to be biphasic, resulting from individual inputs of ICC and SMC.

Toward a better understanding of gastrointestinal nitrergic neuromuscular transmission

BACKGROUND

Nitric oxide (NO) is an important inhibitory neurotransmitter in the gastrointestinal (GI) tract. The majority of nitrergic effects are transduced by NO-sensitive guanylyl cyclase (NO-GC) as the receptor for NO, and, thus, mediated by cGMP-dependent mechanisms. Work carried out during the past years has demonstrated NO to be largely involved in GI smooth muscle relaxation and motility. However, detailed investigation of nitrergic signaling has turned out to be complicated as NO-GC was identified in several different GI cell types such as smooth muscle cells, interstitial cells of Cajal and fibroblast-like cells. With regards to nitrergic neurotransmission, special focus has been placed on the role of interstitial cells of Cajal using mutant mice with reduced populations of ICC. Recently, global and cell-specific knockout mice for enzymes participating in nitrergic signaling have been generated providing a suitable approach to further examine the role of NO-mediated signaling in GI smooth muscle.

PURPOSE

This review discusses the current knowledge on nitrergic mechanisms in gastrointestinal neuromuscular transmission with a focus on genetic models and outlines possible further investigations to gain better understanding on NO-mediated effects in the GI tract.

Telocytes express PDGFRα in the human gastrointestinal tract

Telocytes (TC), a cell population located in the connective tissue of many organs of humans and laboratory mammals, are characterized by a small cell body and extremely long and thin processes. Different TC subpopulations share unique ultrastructural features, but express different markers. In the gastrointestinal (GI) tract, cells with features of TC were seen to be CD34-positive/c-kit-negative and several roles have been proposed for them. Other interstitial cell types with regulatory roles described in the gut are the c-kit-positive/CD34-negative/platelet-derived growth factor receptor α (PDGFRα)-negative interstitial cells of Cajal (ICC) and the PDGFRα-positive/c-kit-negative fibroblast-like cells (FLC). As TC display the same features and locations of the PDGFRα-positive cells, we investigated whether TC and PDGFRα-positive cells could be the same cell type. PDGFRα/CD34, PDGFRα/c-kit and CD34/c-kit double immunolabelling was performed in full-thickness specimens from human oesophagus, stomach and small and large intestines. All TC in the mucosa, submucosa and muscle coat were PDGFRα/CD34-positive. TC formed a three-dimensional network in the submucosa and in the interstitium between muscle layers, and an almost continuous layer at the submucosal borders of muscularis mucosae and circular muscle layer. Moreover, TC encircled muscle bundles, nerve structures, blood vessels, funds of gastric glands and intestinal crypts. Some TC were located within the muscle bundles, displaying the same location of ICC and running intermingled with them. ICC were c-kit-positive and CD34/PDGFRα-negative. In conclusion, in the human GI tract the TC are PDGFRα-positive and, therefore, might correspond to the FLC. We also hypothesize that in human gut, there are different TC subpopulations probably playing region-specific roles.

Basal cGMP regulates the resting pacemaker potential frequency of cultured mouse colonic interstitial cells of Cajal

Cyclic guanosine 3',5'-monophosphate (cGMP) inhibited the generation of pacemaker activity in interstitial cells of Cajal (ICCs) from the small intestine. However, cGMP role on pacemaker activity in colonic ICCs has not been reported yet. Thus, we investigated the role of cGMP in pacemaker activity regulation by colonic ICCs. We performed a whole-cell patch-clamp and Ca(2+) imaging in cultured ICCs from mouse colon. 1H-[1,2,4]Oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, an inhibitor of guanylate cyclase) increased the pacemaker potential frequency, whereas zaprinast (an inhibitor of phosphodiesterase) and cell-permeable 8-bromo-cGMP decreased the pacemaker potential frequency. KT-5823 (an inhibitor of protein kinase G [PKG]) did not affect the pacemaker potential. L-N(G)-nitroarginine methyl ester (L-NAME, an inhibitor of nitric oxide [NO] synthase) increased the pacemaker potential frequency, whereas (±)-S-nitroso-N-acetylpenicillamine (SNAP, a NO donor) decreased the pacemaker potential frequency. Glibenclamide (an ATP-sensitive K(+) channel blocker) did not block the effects of cell-permeable 8-bromo-cGMP and SNAP. Recordings of spontaneous intracellular Ca(2+) ([Ca(2+)]i) oscillations revealed that ODQ and L-NAME increased [Ca(2+)]i oscillations. In contrast, zaprinast, 8-bromo cGMP, and SNAP decreased the [Ca(2+)]i oscillations. Basal cGMP levels regulate the resting pacemaker potential frequency by the alteration on Ca(2+) release via a PKG-independent pathway. Additionally, the endogenous release of NO seems to be responsible maintaining basal cGMP levels in colonic ICCs.

Correlation of cellular expression with function of NO-sensitive guanylyl cyclase in the murine lower urinary tract

The action of nitric oxide (NO) to stimulate NO-sensitive guanylyl cyclase (NO-GC), followed by production of cGMP, and eventually to cause smooth muscle relaxation is well known. In the lower urinary tract (LUT), in contrast to the cardiovascular system and the gastrointestinal tract, specific localization in combination with function of NO-GC has not been investigated to date. Consequently, little is known about the mechanisms regulating relaxation of the lower urinary tract in general and the role of NO-GC-expressing cells in particular. To study the distribution and function of NO-GC in the murine lower urinary tract, we used internal urethral sphincter and bladder detrusor from global (GCKO) and smooth muscle cell-specific (SM-GCKO) NO-GC knock-out mice for immunohistochemical analyses and organ bath experiments. In urethral sphincter, NO-GC-positive immunofluorescence was confined to smooth muscle cells (SMCs). Deletion of NO-GC in SMCs abolished NO-induced relaxation. In bladder detrusor, exposure to NO did not cause relaxation although immunohistochemistry uncovered the existence of NO-GC in the tissue. In contrast to the urethral sphincter, expression of NO-GC in bladder detrusor was limited to platelet-derived growth factor receptor α (PDGFRα)-positive interstitial cells. In conclusion, NO-GC found in SMCs of the urethral sphincter mediates NO-induced relaxation; bladder detrusor is unique as NO-GC is not expressed in SMCs and, thus, NO does not induce relaxation. Nevertheless, NO-GC expression was found in PDGFRα-positive interstitial cells of the murine bladder with an as yet unknown function. Further investigation is needed to clarify the role of NO-GC in the detrusor.

Cell-specific deletion of nitric oxide-sensitive guanylyl cyclase reveals a dual pathway for nitrergic neuromuscular transmission in the murine fundus

BACKGROUND & AIMS

It is not clear how nitric oxide (NO) released from enteric neurons relaxes gastrointestinal (GI) smooth muscle. In analogy to the vascular system, NO might directly induce relaxation of smooth muscle cells (SMCs) by acting on its receptor, NO-sensitive guanylyl cyclase (NO-GC). Alternatively, intermediate cells, such as the interstitial cells of Cajal (ICCs), might detect nitrergic signals to indirectly regulate smooth muscle tone, and thereby regulate the motor function of the GI tract. We investigated the role of ICCs and SMCs in nitrergic relaxation using mice with cell-specific disruption of the gene encoding the β1 subunit of NO-GC (GUCY1B3).

METHODS

We created mice that lack NO-GC specifically in SMCs (SM-guanylyl cyclase knockout [GCKO]), ICCs (ICC-GCKO), or both (SM/ICC-GCKO). We investigated the effects of exogenous and endogenous NO on murine fundus using isometric force studies. Total gut transit time was measured to monitor the functional consequences of NO-GC deletion on GI motility in vivo.

RESULTS

NO-GC is expressed in ICC and SMC. Deletion of the NO receptor from SMCs incompletely reduced NO-induced fundus relaxation, which was hardly affected after ICC-specific deletion. Gut transit time did not change in SM-GCKO or ICC-GCKO mice compared with control mice. However, nitrergic relaxation was not observed in SM/ICC-GCKO mice, which had increased gut transit time compared with controls.

CONCLUSIONS

In mice, NO-GC is the only NO receptor to relax the fundus; deletion of NO-GC from the combination of SMCs and ICCs blocks nitrergic signaling. Therefore, ICCs and SMCs jointly mediate the relaxant effect of enteric NO.

Heme deficiency of soluble guanylate cyclase induces gastroparesis

BACKGROUND

Soluble guanylate cyclase (sGC) is the principal target of nitric oxide (NO) to control gastrointestinal motility. The consequence on nitrergic signaling and gut motility of inducing a heme-free status of sGC, as induced by oxidative stress, was investigated.

METHODS

sGCβ1 (H105F) knock-in (apo-sGC) mice, which express heme-free sGC that has basal activity, but cannot be stimulated by NO, were generated.

KEY RESULTS

Diethylenetriamine NONOate did not increase sGC activity in gastrointestinal tissue of apo-sGC mice. Exogenous NO did not induce relaxation in fundic, jejunal and colonic strips, and pyloric rings of apo-sGC mice. The stomach was enlarged in apo-sGC mice with hypertrophy of the muscularis externa of the fundus and pylorus. In addition, gastric emptying and intestinal transit were delayed and whole-gut transit time was increased in the apo-sGC mice, while distal colonic transit time was maintained. The nitrergic relaxant responses to electrical field stimulation at 1-4 Hz were abolished in fundic and jejunal strips from apo-sGC mice, but in pyloric rings and colonic strips, only the response at 1 Hz was abolished, indicating the contribution of other transmitters than NO.

CONCLUSIONS & INFERENCES

The results indicate that the gastrointestinal consequences of switching from a native sGC to a heme-free sGC, which cannot be stimulated by NO, are most pronounced at the level of the stomach establishing a pivotal role of the activation of sGC by NO in normal gastric functioning. In addition, delayed intestinal transit was observed, indicating that nitrergic activation of sGC also plays a role in the lower gastrointestinal tract.

P2Y(1) knockout mice lack purinergic neuromuscular transmission in the antrum and cecum

BACKGROUND

Pharmacological studies using selective P2Y(1) antagonists, such as MRS2500, and studies with P2Y(1)(-/-) knockout mice have demonstrated that purinergic neuromuscular transmission is mediated by P2Y(1) receptors in the colon. The aim of the present study was to test whether P2Y(1) receptors are involved in purinergic neurotransmission in the antrum and cecum.

METHODS

Microelectrode recordings were performed on strips from the antrum and cecum of wild type animals (WT) and P2Y(1)(-/-) mice.

KEY RESULTS

In the antrum, no differences in resting membrane potential and slow wave activity were observed between groups. In WT animals, electrical field stimulation elicited a MRS2500-sensitive inhibitory junction potential (IJP). In P2Y(1)(-/-) mice, a nitrergic IJP (N(ω) -nitro-l-arginine-sensitive), but not a purinergic IJP was recorded. This IJP was equivalent to the response obtained in strips from WT animals previously incubated with MRS2500. Similar results were obtained in the cecum: 1- the purinergic IJP (MRS2500-sensitive) recorded in WT animals was absent in P2Y(1)(-/-) mice 2- nitrergic neurotransmission was preserved in both groups. Moreover, 1- spontaneous IJP (MRS2500-sensitive) could be recorded in WT, but not in P2Y(1)(-/-) mice 2- MRS2365 a P2Y(1) agonist caused smooth muscle hyperpolarization in WT, but not in P2Y(1) (-/-) animals, and 3- β-NAD caused smooth muscle hyperpolarization both in WT and P2Y(1)(-/-) animals.

CONCLUSIONS & INFERENCES

1- P2Y(1) receptor is the general mechanism of purinergic inhibition in the gastrointestinal tract, 2- P2Y(1)(-/-) mouse is a useful animal model to study selective impairment of purinergic neurotransmission and 3- P2Y(1)(-/-) mouse might help in the identification of purinergic neurotransmitter(s).

Relieving visceral hyperalgesia effect of Kangtai capsule and its potential mechanisms via modulating the 5-HT and NO level in vivo

Kangtai capsule (KT) is one type of traditional Chinese medicine preparation derived from the proved recipe, which was frequently applied as an effective clinical treatment of IBS. However, there still lack the reasonable and all-round analytical approach and the scientific studies on its underlying mechanisms. Therefore, our study aimed to develop the novel method for evaluating its quality as well as to interpret the potential mechanisms. In our study, high performance liquid chromatography (HPLC) fingerprint was applied to provide a chemical profile of KT. The neonatal maternal separation (NMS) on Sprague-Dawley pups was employed to evaluate the therapeutic effect of KT by virtue of various parameters including visceral hyperalgesia, serum nitric oxide (NO) level, and tissue 5-hydroxytryptamine (5-HT) level. Consequently, a chromatographic condition, which was carried at 30°C with a flow rate of 0.5 ml/min on AQUA 3μ C18 column with mobile phase of acetonitrile and water-phosphoric acid (100:0.1, v/v), was established to give a common fingerprint chromatography under 254 nm with a similarity index of 0.963 within ten batches of KT samples. On the NMS model, KT markedly elevated the pain threshold of NMS rats. Furthermore, KT at three doses significantly decreased 5-HT content from distal colon of visceral hyperalgesia rats induced by NMS, while the significant decrease of 5-HT content in serum was only observed in the group with KT at high dose. However, compared with that in NMS rats without KT, there was no apparent difference of 5-HT level from brain issue in the rats with various doses. Besides, KT could substantially elevate the concentration of NO in the serum. The results showed our study developed the simple, rapid, accurate, reproducible qualitative and quantitative analysis by HPLC fingerprint for the quality control for KT. Data from the pharmacological investigation suggested that the curative effect of KT to the visceral hypersensitivity may be concerned with the level of 5-HT and NO in vivo, promising its potential in irritable bowel syndrome treatment.

NO/cGMP: the past, the present, and the future

The NO/cGMP signalling cascade participates in the regulation of physiological parameters such as smooth muscle relaxation, inhibition of platelet aggregation, and neuronal transmission. cGMP is formed in response to nitric oxide (NO) by NO-sensitive guanylyl cyclases that exist in two isoforms (NO-GC1 and NO-GC2). Much has been learned about the regulation of NO-GC; however the precise role of cGMP in complex physiological and especially in pathophysiological settings and its alteration by biological factors needs to be established. Despite reports on a variety of cGMP-independent NO effects, KO mice with a complete lack of NO-GC provide evidence that the vasorelaxing and platelet-inhibiting effects of NO are solely mediated by NO-GC. Isoform-specific KOs demonstrate that low cGMP increases are sufficient to induce smooth muscle relaxation and that either NO-GC isoform is sufficient in most instances outside the central nervous system. In the neuronal system, however, the NO-GC isoforms obviously serve distinct functions as both isoforms are required for long-term potentiation and NO-GC1 was shown to enhance glutamate release in excitatory neurons in the hippocampal CA1 region by gating HCN channels. Future studies have to clarify the role of NO-GC2, to show whether HCN channels are general targets of cGMP in the nervous system and whether the NO/cGMP signalling cascade participates in synaptic transmission in other brain regions.

Preserved fertility despite erectile dysfunction in mice lacking the nitric oxide receptor

Nitric oxide (NO) and cGMP have been shown to be important mediators of penile erection. Erectile dysfunction may result from reduced or non-functional signal transduction within this cascade. There is, however, some inconsistency in the available data as mice lacking NO synthases (endothelial and neuronal nitric oxide synthase, or both) appear to be fertile whereas mice deficient in cGMP-dependent protein kinase I (PKGI) suffer from erectile dysfunction. To clarify this discrepancy we performed studies on mice lacking the NO receptor NO-sensitive guanylyl cyclase (NO-GC). In addition, we generated cell-specific NO-GC knockout (KO) lines to investigate the function of NO in individual cell types. NO-GC was specifically deleted in smooth muscle or endothelial cells (SM-guanylyl cyclase knockout (SM-GCKO) and EC-GCKO, respectively) and these KO lines were compared with total knockouts (GCKO) and wild-type animals. We investigated expression of NO-GC, NO-induced relaxation of corpus cavernosum smooth muscle and their ability to generate offspring. NO-GC-positive immunostaining was detected in smooth muscle and endothelial cells of murine corpus cavernosum but not in interstitial cells of Cajal. NO released from NO donors as well as from nitrergic neurons failed to relax precontracted corpus cavernosum from GCKO mice in organ bath experiments. Similar results were obtained in corpus cavernosum from SM-GCKO mice whereas deletion of NO-GC in endothelial cells did not affect relaxation. The lack of NO-induced relaxation in GCKO animals was not compensated for by guanosine 3,5-cyclic monophosphate (cGMP) signalling. To our surprise, GCKO males were fertile although their ability to produce offspring was decreased. Our data show that deletion of NO-GC specifically in smooth muscle cells abolishes NO-induced corpus cavernosum relaxation but does not lead to infertility.

Platelet-derived growth factor receptor α (PDGFRα)-expressing "fibroblast-like cells" in diabetic and idiopathic gastroparesis of humans

BACKGROUND

Emerging evidence suggests that "fibroblast-like cells" (FLC) may play a role in the regulation of gastrointestinal (GI) motor function. FLC are ultrastructurally distinct from other interstitial cells, including interstitial cells of Cajal (ICC), and express small-conductance Ca(2+) -activated K(+) channels (SK3). In mice, platelet-derived growth factor receptor α (PDGFRα) antibody has also been shown to label FLC. The aims of this study were to determine the morphology and distribution of PDGFRα-immunoreactive (ir) FLC in human gastric muscle and to determine if FLC are altered in gastroparesis, where ICC are reduced.

METHODS

Full thickness gastric body biopsies from five healthy subjects, 10 diabetic, and 10 idiopathic gastroparesis patients were immunolabeled using SK3 and PDGFRα staining for FLC and Kit staining for ICC. Intramuscular FLC and ICC were quantified.

KEY RESULTS

Intramuscular PDGFRα-ir cells had slender cell bodies and long, thin processes and were more abundant in the longitudinal compared with the circular muscle. In the region of myenteric plexus, FLC had smaller, rounder cell bodies with 3-4 processes and formed networks, often around ganglia. All SK3-ir cell structures showed complete overlap with PDGFRα-ir. FLC were in close proximity to ICC, but their cell bodies did not overlap. No differences were seen in the distribution, morphology, or overall numbers of FLC in gastroparesis patients.

CONCLUSIONS & INFERENCES

In conclusion, PDGFRα identifies FLC in human gastric smooth muscle. FLC were not altered in distribution or overall numbers in gastroparesis. Additional studies are required to determine their role in human GI function.

Relative contribution of SKCa and TREK1 channels in purinergic and nitrergic neuromuscular transmission in the rat colon

Purinergic and nitrergic neurotransmission predominantly mediate inhibitory neuromuscular transmission in the rat colon. We studied the sensitivity of both purinergic and nitrergic pathways to spadin, a TWIK-related potassium channel 1 (TREK1) inhibitor, apamin, a small-conductance calcium-activated potassium channel blocker and 1H-[1,2,4]oxadiazolo[4,3-α]quinoxalin-1-one (ODQ), a specific inhibitor of soluble guanylate cyclase. TREK1 expression was detected by RT-PCR in the rat colon. Patch-clamp experiments were performed on cells expressing hTREK1 channels. Spadin (1 μM) reduced currents 1) in basal conditions 2) activated by stretch, and 3) with arachidonic acid (AA; 10 μM). l-Methionine (1 mM) or l-cysteine (1 mM) did not modify currents activated by AA. Microelectrode and muscle bath studies were performed on rat colon samples. l-Methionine (2 mM), apamin (1 μM), ODQ (10 μM), and N(ω)-nitro-l-arginine (l-NNA; 1 mM) depolarized smooth muscle cells and increased motility. These effects were not observed with spadin (1 μM). Purinergic and nitrergic inhibitory junction potentials (IJP) were studied by incubating the tissue with l-NNA (1 mM) or MRS2500 (1 μM). Both purinergic and nitrergic IJP were unaffected by spadin. Apamin reduced both IJP with a different potency and maximal effect for each. ODQ concentration dependently abolished nitrergic IJP without affecting purinergic IJP. Similar effects were observed in hyperpolarizations induced by sodium nitroprusside (1 μM) and nitrergic relaxations induced by electrical stimulation. We propose a pharmacological approach to characterize the pathways and function of purinergic and nitrergic neurotransmission. Nitrergic neurotransmission, which is mediated by cyclic guanosine monophosphate, is insensitive to spadin, an effective TREK1 channel inhibitor. Both purinergic and nitrergic neurotransmission are inhibited by apamin but with different relative sensitivity.