Role of Ca2+-sensitization in attenuated carbachol-induced contraction of the colon in a rat model of colitis

Stretch-Induced Down-Regulation of HCN2 Suppresses Contractile Activity

Although hyperpolarization-activated and cyclic nucleotide-gated 2 channels (HCN2) are expressed in multiple cell types in the gut, the role of HCN2 in intestinal motility is poorly understood. HCN2 is down-regulated in intestinal smooth muscle in a rodent model of ileus. Thus, the purpose of this study was to determine the effects of HCN inhibition on intestinal motility. HCN inhibition with ZD7288 or zatebradine significantly suppressed both spontaneous and agonist-induced contractile activity in the small intestine in a dose-dependent and tetrodotoxin-independent manner. HCN inhibition significantly suppressed intestinal tone but not contractile amplitude. The calcium sensitivity of contractile activity was significantly suppressed by HCN inhibition. Inflammatory mediators did not affect the suppression of intestinal contractile activity by HCN inhibition but increased stretch of the intestinal tissue partially attenuated the effects of HCN inhibition on agonist-induced intestinal contractile activity. HCN2 protein and mRNA levels in intestinal smooth muscle tissue were significantly down-regulated by increased mechanical stretch compared to unstretched tissue. Increased cyclical stretch down-regulated HCN2 protein and mRNA levels in primary human intestinal smooth muscle cells and macrophages. Overall, our results suggest that decreased HCN2 expression induced by mechanical signals, such as intestinal wall distension or edema development, may contribute to the development of ileus.

Sishen Pill Maintained Colonic Mucosal Barrier Integrity to Treat Ulcerative Colitis via Rho/ROCK Signaling Pathway

Sishen Pill (SSP) is a classical prescription of traditional Chinese medicine and often used to treat gastrointestinal diseases, including ulcerative colitis (UC). However, its mechanism is still unclear. We aimed to determine the mechanism of SSP in the treatment of UC by investigating if it maintains the integrity of the intestinal mucosal barrier via the Rho A/Rho kinase (ROCK) signaling pathway. Administration of 2,4,6-trinitrobenzene sulfonic acid (TNBS) successfully induced chronic UC in rats, while the treatment effect of SSP was evaluated by body weight change, colonic length, colonic weight, colonic weight index, histological injury score, and pathological injury score after colitis rats were treated for 7 days. TNF-α and IL-1β levels were analyzed by ELISA, and the proteins of PI3K/Akt and RhoA/ROCK signaling pathway and junction proteins expression were measured by western blotting assay, and the distribution of Claudin 5 was shown by immunofluorescence. SSP significantly improved the clinical symptoms of colitis in rats and reduced the expression of p-RhoA, ROCK1, PI3K, and Akt in the colon mucosa, while it increased the expression of p-Rac and related proteins (Claudin-5, JAM1, VE-cadherin, and Connexin 43). In addition, SSP increased p-AMPKα and PTEN proteins expression, decreased Notch1 level, and hinted that activation of the PI3K/Akt signaling pathway was inhibited. In conclusion, SSP effectively treated chronic colitis induced by TNBS, which may have been achieved by inhibiting PI3K/Akt signal to suppress activation of the Rho/ROCK signaling pathway to finally maintain the integrity of the intestinal mucosal barrier.

The effect of sphingosine-1-phosphate on colonic smooth muscle contractility: Modulation by TNBS-induced colitis

Aim

Increased levels of circulating sphingosine-1-phosphate (S1P) have been reported in ulcerative colitis. The objective of this study was to examine the effect of S1P on colonic smooth muscle contractility and how is it affected by colitis.

Methods

Colonic inflammation was induced by intrarectal administration of trinitrobenzene sulfonic acid. Five days later colon segments were isolated and used for contractility experiments and immunoblotting.

Results

S1P contracted control and inflamed colon segments and the contraction was significantly greater in inflamed colon segments. S1P-induced contraction was mediated by S1PR1 and S1PR2 in control and S1PR2 in inflamed colon segments. S1PR3 did not play a significant role in S1P-induced contractions in control or inflamed colon. S1PR1, S1PR2 and S1PR3 proteins were expressed in colon segments from both groups. The expression of S1PR1 and S1PR2 was significantly enhanced in control and inflamed colon segments, respectively. S1PR3 levels however were not significantly different between the two groups. Nifedipine significantly reduced S1P-induced contraction in control but not inflamed colon segments. Thapsigargin significantly reduced S1P-induced contraction of the inflamed colon. GF 109203X and Y-27632, alone abolished S1P-induced contraction of the control but not inflamed colon segments. Combination of GF 109203X, Y-27632 and thapsigargin abolished S1P-induced contraction of inflamed colon segments.

Conclusion

S1P contracted control colon via S1PR1 and S1PR2 and inflamed colon exclusively via S1PR2. Calcium influx (control) or release (inflamed) and calcium sensitization are involved in S1P-induced contraction. Exacerbated response to S1P in colitic colon segments may explain altered colonic motility reported in patients and experimental models of inflammatory bowel disease.

Ionic Conductance(s) in Response to Post-junctional Potentials

The gastrointestinal motility is regulated by extrinsic and intrinsic neural regulation. Intrinsic neural pathways are controlled by sensory input, inter-neuronal relay and motor output. Enteric motor neurons release many transmitters which affect post-junctional responses. Post-junctional responses can be excitatory and inhibitory depending on neurotransmitters. Excitatory neurotransmitters induce depolarization and contraction. In contrast, inhibitory neurotransmitters hyperpolarize and relaxe the gastrointestinal smooth muscle. Smooth muscle syncytium is composed of smooth muscle cells, interstitial cells of Cajal and platelet-derived growth factor receptor α-positive (PDGFRα(+)) cells (SIP syncytium). Specific expression of receptors and ion channels in these cells can be affected by neurotransmitters. In recent years, molecular reporter expression techniques are able to study the properties of ion channels and receptors in isolated specialized cells. In this review, we will discuss the mechanisms of ion channels to interpret the post-junctional responses in the gastrointestinal smooth muscles.

A role of intestine in hypertension: mechanism of suppression of intestinal Na-H exchanger isoform-3 in spontaneously hypertensive rats

The main objective of this study was to investigate the role and the underlying mechanism of Na-H exchanger-3 (NHE-3) expression in spontaneously hypertensive rat (SHR) intestine. Expression of colonic and ileal NHE-3 isoform, its regulatory factor-1 (NHERF-1) and cyclic GMP kinase II (cGKII) were examined using western blot analysis. Since NHE-3 activity is regulated by its abundance on the plasma membrane, its levels were also examined in lipid rafts-enriched membrane fractions. The lipid rafts fractions were characterized by examining the concentration of flotillin-1 and caveolin-1, total protein, and cholesterol. Twelve-weeks-old SHR used in this study developed significant hypertension, proteinuria, and renal and cardiac hypertrophy. These changes were significantly reversed by captopril treatment. There was a significant decrease in the levels of NHE-3 and NHERF-1 proteins, and sodium pump activity, but an increase in the cGKII levels in both tissues from SHR. Reduction in NHERF-1 levels was reversed by captopril but not of the other proteins. Cholesterol profile was significantly different in SHR colon as compared to normo-tensive Wistar Kyoto rats. These findings suggest that suppression of NHE-3 in intestine is a counteracting mechanism of hypertension and is regulated by NHERF-1 through cGKII activation in SHR. NHE-3 suppression together with decrease in the sodium pump activity would accumulate intracellular Na(+) and may contribute to the reported hypertension-induced tissue damage in the GI-tract.

Mechanisms of smooth muscle responses to inflammation

BACKGROUND

Inflammation-induced changes in smooth muscle may be the consequence of changes in the properties of smooth muscle itself, in the control by nerves and hormones, in the microenvironment, or in the balance of constitutive or induced mediators. A general concept is that the specific characteristics and effects of inflammation can be linked to the nature of the infiltrate and the associated mediators, which are dictated predominantly by the immune environment. Inflammatory mediators may regulate smooth muscle function by directly acting on smooth muscle cells or, indirectly, through stimulation of the release of mediators from other cells. In addition, smooth muscle is not a passive bystander during inflammation and our knowledge of molecular signaling pathways that control smooth muscle function, and the contribution of the immune mechanisms to smooth muscle homeostasis, has expanded greatly in the last decade. Recent studies also demonstrated the relevance of extracellular proteases, of endogenous or exogenous origin, redox imbalance, or epigenetic mechanisms, to gastrointestinal dismotility and inflammation in the context of functional and organic disorders.

PURPOSE

In this review we discuss the various types of inflammation and the established and emerging mechansims of inflammation-induced changes in smooth muscle morphology and function.

Expression of alternatively spliced variants of Na-Ca-exchanger-1 in experimental colitis: role in reduced colonic contractility

Inflammation-induced colonic motility dysfunction is associated with a disturbance in Ca(2+) ion transporting mechanisms. The main objective of this study was to identify the types of Na-Ca-exchanger-1 (NCX-1) variants expressed in the rat colon, and how this was affected by colitis. In addition, the effect of colitis on the possible involvement of NCX-1 in the reduced carbachol-induced contraction of the rat colon was examined. Colitis was induced in male Sprague-Dawley rats by intra-rectal instillation of trinitrobenzenesulphonic acid (TNBS). Animals were killed on day 5. Colitis was characterized by estimating myeloperoxidase (MPO) activity, body weight, and histological scores. NCX-1 mRNA and protein variants were confirmed by RT-PCR coupled nucleotide sequencing and by Western blot analysis, respectively. Contractility of the colon segments was studied using standard procedure. There was a significant reduction in body weight of TNBS-treated rats. A significant increase in MPO activity and infiltration of inflammatory cells were observed in the inflamed rat colon. RT-PCR coupled nucleotide sequencing identified NCX-1.3 mRNA variant containing exons B and D. Western blot analysis confirmed 70 and 120 kDa molecular mass NCX-1 protein variants in rat colon. There was no significant difference (p > 0.05) in the level of NCX-1 protein variants in inflamed colon as compared to non-colitis controls. Functional experiments demonstrated that NCX in reverse mode played a role in carbachol-induced contraction of colon, and this was not affected by colitis. These findings demonstrated expression of a NCX-1.3 mRNA splice variant, and 70 and 118 kDa protein variants. Inhibition of the reverse mode of NCX-1 was not different in reduced carbachol-induced contraction between the groups. These findings are interpreted to suggest that NCX-1, though expressed did not play a role in reduced contractility in experimental colitis.

The contribution of protein kinase C and CPI-17 signaling pathways to hypercontractility in murine experimental colitis

BACKGROUND

Colonic smooth muscle contractility is altered in colitis, and several protein kinase pathways can mediate colonic smooth muscle contraction. In the present study, we investigated whether protein kinase C (PKC) pathways also play a role in colonic hypercontractility observed during T(H) 2 colitis in BALB/c mice.

METHODS

Colitis was induced in BALB/c mice by provision of 5% dextran sodium sulfate (DSS) for 7 days. Changes in smooth muscle contractility were examined using dissected circular smooth muscle preparations from the distal colon. The contribution of conventional and novel PKC isozymes to the hypercontractile response was examined with pharmacological PKC inhibitors. Western blot analyses were used to examine protein expression and phosphorylation changes.

KEY RESULTS

Colonic smooth muscle was associated with inflammation-induced hypercontractility and altered PKC expression. Carbachol-induced peak (phasic) and sustained (tonic) contractions were increased. Chelerythrine was the most effective PKC inhibitor of both phasic and tonic contractions. There was no general difference in the percent contribution of conventional and novel PKC isozymes toward the DSS-induced hypercontractility, but inhibition of sustained force with GF109203x was higher for inflamed muscle. The CPI-17 phosphorylation was equally suppressed in both normal and DSS conditions by Gö6976 and chelerythrine, but only for the phasic component of contraction.

CONCLUSIONS & INFERENCES

The outcomes suggest that both conventional and novel PKC isozymes contribute to the phasic and tonic contractile components of BALB/c colonic circular smooth muscle under normal conditions, with novel PKC isozymes having a greater contribution to the tonic contraction. However, no effect of inflammation was observed on the relative contribution of PKC and CPI-17 toward the observed hypercontractility.

Contribution of Rho-kinase to membrane excitability of murine colonic smooth muscle

BACKGROUND AND PURPOSE

The Rho-kinase pathway regulates agonist-induced contractions in several smooth muscles, including the intestine, urinary bladder and uterus, via dynamic changes in the Ca(2+) sensitivity of the contractile apparatus. However, there is evidence that Rho-kinase also modulates other cellular effectors such as ion channels.

EXPERIMENTAL APPROACH

We examined the regulation of colonic smooth muscle excitability by Rho-kinase using conventional microelectrode recording, isometric force measurements and patch-clamp techniques.

KEY RESULTS

The Rho-kinase inhibitors, Y-27632 and H-1152, decreased nerve-evoked on- and off-contractions elicited at a range of frequencies and durations. The Rho-kinase inhibitors decreased the spontaneous contractions and the responses to carbachol and substance P independently of neuronal inputs, suggesting Y-27632 acts directly on smooth muscle. The Rho-kinase inhibitors significantly reduced the depolarization in response to carbachol, an effect that cannot be due to regulation of Ca(2+) sensitization. Patch-clamp experiments showed that Rho-kinase inhibitors reduce GTPγS-activated non-selective cation currents.

CONCLUSIONS AND IMPLICATIONS

The Rho-kinase inhibitors decreased contractions evoked by nerve stimulation, carbachol and substance P. These effects were not solely due to inhibition of the Ca(2+) sensitization pathway, as the Rho-kinase inhibitors also inhibited the non-selective cation conductances activated by excitatory transmitters. Thus, Rho-kinase may regulate smooth muscle excitability mechanisms by regulating non-selective cation channels as well as changing the Ca(2+) sensitivity of the contractile apparatus.

Mechanism of Rho-kinase-mediated Ca2+-independent contraction in aganglionic smooth muscle in a rat model of Hirschsprung's disease

PURPOSE

Lack of ganglion cells is the main cause of bowel movement disorder in Hirschsprung's disease. Because smooth muscle is the primary organ, the properties of intestinal smooth muscle need to be investigated. We therefore investigated the reactivity of the contractile system and the mechanism of contraction in aganglionic intestinal smooth muscle.

METHODS

Colonic smooth muscle strips from endothelin-B receptor gene-deficient [EDNRB(-/-)] rats were loaded with the Ca(2+) indicator dye fura-PE3/AM and changes in fluorescence intensity were monitored. The intracellular calcium concentration ([Ca(2+)]i) and force development in the strips were measured simultaneously.

RESULTS

The force induced by 10 microM substance P (SP) was higher than that induced by 60 mM K(+) depolarization (control), whereas [Ca(2+)]i elevation induced by 10 microM SP was less than that induced by 60 mM K(+) in all segments. Pretreatment with the Rho-kinase inhibitor Y-27632 inhibited force development more strongly in EDNRB(-/-) aganglionic segments than in EDNRB(+/+) ganglionic segments. However, [Ca(2+)]i was higher in EDNRB(-/-) aganglionic segments than in EDNRB(+/+) ganglionic segments.

CONCLUSIONS

The Ca(2+)-independent pathway involving Rho-kinase was hyperactivated in EDNRB(-/-) aganglionic segments. This phenomenon is assumed to compensate for Ca(2+) channel downregulation and Ca(2+)-dependent contraction. From a clinical point of view, the motility of aganglionic intestine would be controllable with the control of Ca(2+)-independent contraction before definitive operations in Hirschsprung's disease.

Curcumin reverses attenuated carbachol-induced contraction of the colon in a rat model of colitis

BACKGROUND

Curcumin ameliorates colitis whether it reverses colitis-induced reduction in colonic contractility remains to be investigated.

OBJECTIVES

To investigate the effect of curcumin on colitis-induced reduction of carbachol-induced contraction in colon segments from rats treated with trinitrobenzenesulphonic acid.

METHODS

Colitis was induced in rats by intra rectal administration of trinitrobenzenesulphonic acid and followed for 5 days. A group of animals which received trinitobenzene sulphonic acids was treated with curcumin (100 mg/Kg and 200 mg/kg body weight) 2 hrs prior to induction of colitis. The controls received phosphate buffered saline in a similar fashion. Markers of inflammation and contractility of colon were assayed using standard procedures.

RESULTS

Induction of colitis was associated with increased myeloperoxidase activity and malondialdehyde levels, gross histological changes characterized by infiltration of inflammatory cells. All these changes were prevented by treatment with curcumin (100 mg/kg). Treatment with curcumin also reduced the histological scores from 3.34+/-0.40 to 1.75+/-0.30 confirming an anti-inflammatory effect of curcumin in this experimental model of colitis. Colonic reactivity to carbachol was decreased in colitis affecting the maximum response but not sensitivity. Treatment with curcumin had no effect on sensitivity of the colon to carbachol in any of the preparations. Curcumin however reversed the decrease in carbachol-induced contraction associated with trinitrobenzenesulphonic acid treatment. The same dose of curcumin had no effect on either the potency of or the maximum response to carbachol in control rats. Tissue expression of NF-kB was increased in colon segments from trinitrobenzenesulphonic acid -treated rats and this was inhibited in rats treated with curcumin.

CONCLUSIONS

Based on these findings it is concluded that curcumin prevented the reduction in carbachol-induced contraction in trinitrobenzenesulphonic acid -treated rats by modulating NF-kB signaling pathway.

Suppression of Na+/H+ exchanger isoform-3 in human inflammatory bowel disease: lack of reversal by 5'-aminosalicylate treatment

OBJECTIVE

Na+/H+ exchanger isoform 3 (NHE-3) is responsible for net uptake of NaCl and water from the gastrointestinal (GI) tract. However, its status in human inflammatory bowel diseases (IBDs) such as ulcerative colitis(UC) and Crohn's disease (CD) remains poorly understood. The aim of this study was to investigate the underlying mechanism of NHE-3 isoform expression and its modulation by 5'-aminosalicylate in human CD and UC.

MATERIAL AND METHODS

Subjects were divided into three groups: 1) controls; 2) untreated/new IBD cases (n = 13) and 3) 5'-aminosalicylate-treated IBD patients (n = 13). Subjects presenting with abdominal pain but with endoscopically normal colons served as normal controls. Inflammation was confirmed by the level of myeloperoxidase (MPO) activity, malondialdehyde (MDA) concentrations and by histologic evaluation. Expressions of NHE-3 protein and mRNA, sodium pump activity and IL-1beta and TNF-alpha mRNA were estimated in the colonic biopsies using ECL-Western blot analysis,reverse transcription-polymerase chain reaction (RT-PCR) and enzyme assays.

RESULTS

The level of NHE-3 protein and sodium pump activity was reduced (p < 0.05) in both the untreated and treated CD and UC patients. NHE-3 mRNA was reduced only in CD patients but not in those with UC. The treatment reversed the symptoms, but levels of MPO activity, MDA concentration, IL-1beta, TNF-alpha and infiltration of inflammatory cells remained high with the exception of IL-1beta mRNA in the treated patients.

CONCLUSIONS

NHE-3 suppression is regulated differentially in CD and UC, which together with suppression of sodium pump activity will reduce NaCl and water uptake from the colonic lumen. These findings suggest a role of TNF-a in the regulation of NHE-3 expression in IBD.

Curcumin attenuates inflammation through inhibition of TLR-4 receptor in experimental colitis

Curcumin, an active ingredient of Curcumin longa mediates its anti-inflammatory effects through inhibition of NFkB. Several pathways including toll-like receptors (TLR) induce NFkB leading to inflammation. In this study, we investigated the effects of curcumin on the expression of TLR-4 and MyD88, the upstream signaling pathway in experimental colitis induced in the Sprague-Dawley male rats by intra-rectal administration of trinitrobenzenesulfonic acid (TNBS). The animals which received TNBS were divided into two groups: Group 1, received aqueous suspension of curcumin (100 mg/Kg body weight) 2 h prior to inducing colitis, and the treatment was repeated every day for 5 days, and Group 2 and non-colitis (Group 3) animals received phosphate buffered saline (PBS) in a similar fashion. Non-colitis animals (Group 4) received curcumin and served as controls. Animals were sacrificed on day 5 post-TNBS by cervical dislocation, colon was taken out, and cleaned with PBS. Levels of TLR-4, MyD88, and NFkB proteins were measured using ECL Western blot analysis, and TLR-4 mRNA by a competitive RT-PCR method. Colitis was confirmed histologically by measuring myeloperoxidase (MPO) activity and malondialdehyde (MDA) levels in the colonic tissues. TNBS-induced increase in the level of MPO activity and MDA concentrations was reversed by curcumin treatment, whereas the same dose of curcumin did not affect their levels in the non-colitis animals. Increases in the levels of TLR-4, MyD88, and NFkB proteins in inflamed tissue were also suppressed significantly by curcumin treatment. The level of TLR-4 mRNA remained unchanged in the colitis animals. These findings demonstrate that signaling pathway of curcumin-induced inhibition of inflammation involves TLR-4 and MyD88, and therefore may serve as an important therapeutic target in IBD.