Colonic Smooth Muscle Cells Research Articles

Endogenous hydrogen sulfide decreases Rho kinase and cGMP‐specific phosphodiesterase (PDE5) activity and induces relaxation of colonic smooth muscle (1110.3)

H2S, synthesized endogenously from L‐cysteine via cystathionine‐γ‐lyase (CSE) and cystathionine‐β‐synthase (CBS), play a role in the regulation of gastrointestinal (GI) motility and secretion. Neither the expression of enzymes nor the mechanism of action of H2S in GI smooth muscle is fully known. Methods: Expression of CSE and CBS was analyzed by RT‐PCR and western blot. The effect of H2S on carbachol (CCh)‐induced Rho kinase activity and sustained contraction, and nitric oxide‐induced PDE5 activity, cGMP formation and muscle relaxation was examined using L‐cysteine (activator of CSE) or NaHS (H2S donor). Results: CSE, but not CBS was expressed in colonic smooth muscle cells of mouse, rabbit and human. CCh‐induced contraction in muscle strips and cells, and increased Rho kinase activity were inhibited by L‐cysteine and NaHS in a concentration‐dependent manner. Inhibition of Rho kinase activity and muscle contraction by L‐cysteine (but not NaHS) was blocked by CSE siRNA and CSE inhibitor, propargylglycine, respectively. L‐cysteine and NaHS also inhibited PDE5 activity, and augmented cGMP formation and muscle relaxation leading to increased (35%) colonic pellet propulsion. Conclusion: Activation of H2S‐producing CSE causes muscle relaxation via a dual mechanism involving inhibition of Rho kinase and PDE5 activity leading to downregulation of RhoA/Rho kinase pathway and upregulation of cGMP/PKG pathway.Grant Funding Source: DK‐28300

Colonic smooth muscle cells and colonic motility patterns as a target for irritable bowel syndrome therapy: mechanisms of action of otilonium bromide.

Otilonium bromide (OB) is a spasmolytic compound of the family of quaternary ammonium derivatives and has been successfully used in the treatment of patients with irritable bowel syndrome (IBS) due to its specific pharmacodynamic effects on motility patterns in the human colon and the contractility of colonic smooth muscle cells. This article examines how. OB inhibits the main patterns of human sigmoid motility in vitro, which are spontaneous rhythmic phasic contractions, smooth muscle tone, contractions induced by stimulation of excitatory motor neurons and contractions induced by direct effect of excitatory neurotransmitters. It does this mainly by blocking calcium influx through L-type calcium channels and interfering with mobilization of cellular calcium required for smooth muscle contraction, thereby limiting excessive intestinal contractility and abdominal cramping. OB also inhibits T-type calcium channels and muscarinic responses. Finally, OB inhibits tachykinin receptors on smooth muscle and primary afferent neurons which may have the joint effect of reducing motility and abdominal pain. All these mechanisms mediate the therapeutic effects of OB in patients with IBS and might be useful in patients with other spastic colonic motility disorders such as diverticular disease.

Advanced glycation end products inhibit intracellular calcium concentration in colon smooth muscle cells in a protein kinase C-dependent manner

Advanced glycation end products inhibit intracellular calcium concentration in colon smooth muscle cells in a protein kinase C-dependent manner

Age‐related changes in mitochondrial function of mouse colonic smooth muscle: beneficial effects of melatonin

Aging is a multifactorial process that involves biochemical, structural, and functional changes in mitochondria. The ability of melatonin to palliate the alterations induced by aging is based on its chronobiologic, antioxidant, and mitochondrial effects. There is little information about the effects of melatonin on the in situ mitochondrial network of aging cells and its physiological implications. We have studied the ability of melatonin to prevent the functional alterations of in situ mitochondria of smooth muscle cells and its impact on contractility. Mitochondrial membrane potential was recorded in isolated colonic smooth muscle cells from young mice (3 month old), aged mice (22-24-month old), and aged mice treated with melatonin (starting at 14-month age). Aging induced a partial mitochondrial depolarization in resting conditions and reduced the depolarizing response to cellular stimulation. Use of oligomycin indicated that aging enhanced the resting activity of the mitochondrial ATP synthase, whereas in young cells, the enzyme operated mainly in reverse mode. Melatonin treatment prevented all these changes. Aging reduced both spontaneous and stimulated contraction of colonic strips and shifted the metabolic dependence of contraction from mitochondria to glycolysis, as indicated the use of mitochondrial and glycolysis inhibitors. These functional alterations were also palliated by melatonin treatment. Aging effects were not related to a decrease in Ca2+ store mobilization, because this was enhanced in aged cells and restored by melatonin. In conclusion, melatonin prevents the age induced in situ mitochondrial potential alterations in smooth muscle cells and the associated changes in contractility and metabolism.

Neo-innervation of a bioengineered intestinal smooth muscle construct around chitosan scaffold

Neuromuscular disorders of the gut result in disturbances in gastrointestinal transit. The objective of this study was to evaluate the neo-innervation of smooth muscle in an attempt to restore lost innervation. We have previously shown the potential use of composite chitosan scaffolds as support for intestinal smooth muscle constructs. However, the constructs lacked neuronal component. Here, we bioengineered innervated colonic smooth muscle constructs using rabbit colon smooth muscle and enteric neural progenitor cells. We also bioengineered smooth muscle only tissue constructs using colonic smooth muscle cells. The constructs were placed next to each other around tubular chitosan scaffolds and left in culture. Real time force generation conducted on the intrinsically innervated smooth muscle constructs showed differentiated functional neurons. The bioengineered smooth muscle only constructs became neo-innervated. The neo-innervation results were confirmed by immunostaining assays. Chitosan supported (1) the differentiation of neural progenitor cells in the constructs and (2) the neo-innervation of non-innervated smooth muscle around the same scaffold.

Magnolol inhibits colonic motility through down-regulation of voltage-sensitive L-type Ca2+ channels of colonic smooth muscle cells in rats

This study aimed to investigate the effect of magnolol (5,5′-diallyl-2,2′-biphenyldiol) on contraction in distal colonic segments of rats and the underlying mechanisms. Colonic segments were mounted in organ baths for isometric force measurement. Whole-cell voltage-sensitive L-type Ca2+ currents were recorded on isolated single colonic smooth muscle cells using patch-clamp technique. The spontaneous contractions and acetylcholine (ACh)- and Bay K 8644-induced contractions were inhibited by magnolol (3–100μM). In the presence of Bay K8644 (100nM), magnolol (10–100μM) inhibited the contraction induced by 10μM ACh. By contrast, tetrodotoxin (100nM) and Nώ-nitro-l-arginine methyl ester (l-NAME 100μM) did not change the inhibitory effect of magnolol (10μM). In addition, magnolol (3–100μM) inhibited the L-type Ca2+ currents. The present results suggest that magnolol inhibits colonic smooth muscle contraction through downregulating L-type Ca2+ channel activity.

Mechanisms of action of otilonium bromide (OB) in human cultured smooth muscle cells and rat colonic strips

The pharmacological properties of otilonium bromide (OB) have been investigated using different experimental models, techniques, and conditions, and consequently, the results are not always easy to compare. The aim of the present work was to investigate the pharmacological properties of OB in human cultured colonic smooth muscle cells (HCSMCs), which is the main target of the drug 'in vivo'. Rat colonic strips were used to confirm the pharmacological properties. Human cultured colonic smooth muscle cells were studied using the calcium imaging technique. Microelectrodes and muscle bath experiments were performed in rat colonic strips. Otilonium bromide (OB) concentration dependently inhibited nifedipine-sensitive calcium transients induced by KCl (EC50 =3.6μM) and BayK8644 (EC50 =4.0μM). All the following experiments were performed in the presence of nifedipine. In HCSMC, carbachol-induced calcium transients were inhibited by OB (EC50 =8.4μM). Carbachol evoked 1-a smooth muscle depolarization (10mV) that was antagonized by 100μM OB; and 2-a contraction that was inhibited by OB (EC50 =13.0μM). 'Non-nitrergic (L-NNA 1mM) non-purinergic (MRS2500 1μM)' conditions were used to elicit endogenous excitatory responses. Electrical field stimulation caused 1-an atropine-sensitive excitatory junction potential that was inhibited by OB (EC50 =8.9μM) and 2-an atropine-sensitive contraction that was inhibited by OB (EC50 =7.3μM). In HCSMC, neurokinin A (NKA) and CaCl2 induced calcium transients that were inhibited by OB (NKA: EC50 =11.7μM; CaCl2 : EC50 =17.5μM). Otilonium bromide causes inhibition of L-/T-type calcium channels, muscarinic, and tachykininergic responses that acting together explain the pharmacological properties of the compound.

Estradiol regulates the expression of small conductance Ca(2)+ activated K(+) channel 3 in rat colonic smooth muscle cells in an estrogen receptor α-dependent manner

To explore the effects and possible mechanism of 17β-estradiol on the expression of small conductance Ca(2+) activated K(+) channel 3 (SK3) in rat colonic smooth muscle cells (SMC). The SMC isolated from male SD rats by enzymolysis were cultured. And double immunofluorescence staining was used to detect the co-expression of SK3 and α-actin. Colonic SMC were cultured with different concentrations of 17β-estradiol for 24 h or with 50 nmol/L 17β-estradiol at different time points respectively. The expressions of SK3 in colonic SMC were measured by real-time quantitative reverse transcription (qRT)-PCR and Western blotting. The effects of estrogen receptor (ER) inhibitor ICI 182780, albumin bovine serum-17β-estradiol (BSA-E2), ERα selective agonist propyl pyrazole triol (PPT) and ERβ selective agonist diarylpropionitrile (DPN) on SK3 expression were observed. Double immunofluorescence staining showed that SK3 and α-actin co-expressed in cultured colonic SMC. The expression of SK3 of 17β-estradiol at different concentration (10, 50 nmol/L) significantly higher than the control group (protein: 0.217 ± 0.030 and 0.321 ± 0.077 vs 0.103 ± 0.063, mRNA: 1.872 ± 0.606 and 2.967 ± 0.659 vs 0.813 ± 0.202, all P < 0.05). And 50 nmol/L was the most effective in vitro concentration. The peak expression of SK3 appeared at 12 and 24 hour (2.91 and 3.30-fold in protein vs 3.46 and 3.37-fold in mRNA respectively, all P < 0.05). The protein levels of SK3 in ICI 182780 plus 17β-estradiol group was less than 17β-estradiol group (0.111 ± 0.050 vs 0.351 ± 0.084, P < 0.05). But it was not influenced by BSA-E2. The expressions of SK3 in PPT and E2 groups were both higher than control group (0.270 ± 0.071, 0.309 ± 0.052 vs 0.087 ± 0.018, both P < 0.05) . However DPN had no effect on SK3 protein levels. SK3 is localized in rat colonic SMC. And 17β-estradiol increases its expression in an ERα-dependent manner.

MTOR pathway and Ca2+ stores mobilization in aged smooth muscle cells

Aging is considered to be driven by the so called senescence pathways, especially the mTOR route, although there is almost no information on its activity in aged tissues. Aging also induces Ca²⁺ signal alterations, but information regarding the mechanisms for these changes is almost inexistent. We investigated the possible involvement of the mTOR pathway in the age-dependent changes on Ca²⁺ stores mobilization in colonic smooth muscle cells of young (4 month old) and aged (24 month old) guinea pigs. mTORC1 activity was enhanced in aged smooth muscle, as revealed by phosphorylation of mTOR and its direct substrates S6K1 and 4E-BP1. Mobilization of intracellular Ca²⁺ stores through IP3R or RyR channels was impaired in aged cells, and it was facilitated by mTOR and by FKBP12, as indicated by the inhibitory effects of KU0063794 (a direct mTOR inhibitor), rapamycin (a FKBP12-mediated mTOR inhibitor) and FK506 (an FKBP12 binding immunosuppressant). Aging suppressed the facilitation of the Ca²⁺ mobilization by FKBP12 but not by mTOR, without changing the total expression of FKBP12 protein. In conclusion, or study shows that in smooth muscle aging enhances the constitutive activity of mTORC1 pathway and impairs Ca²⁺ stores mobilization by suppression of the FKBP12-induced facilitation of Ca²⁺ release.

Sa2066 The Provocative Water Load Test Evokes Nausea and Gastric Dysrhythmias in Patients With Unexplained Chronic Nausea and Vomiting

Previous studies found that mechanical stretch in bowel obstruction markedly induced gene expression of COX-2, but not COX-1, in colonic smooth muscle cells (SMCs). The aims of the present study were to determine whether genes encoding individual prostaglandin synthases are mechanically responsive, and whether the composition of prostaglandins resulting from obstruction differs from that in inflammation. Methods: Partial colon obstruction was induced with a silicon band implanted surgically in the distal colon of male SpragueDawley rats. Static mechanical stretch (18% elongation) was mimicked in vitro in the culture of rat colonic circular SMCs with a Flexercell FX-4000 System. Rat colon inflammation was induced by manipulation of the colonic surface with wet cotton applicators. Results: 1. Quantitative RT-PCR found that the expression of PGDS and PGIS genes was not significantly changed on day 3 of obstruction. However, the membrane bound PGES-1 (mPGES-1) mRNA was significantly up-regulated in the obstructed segment, whereas mRNAs for other two types of PGES, cytosolic PGES and mPGES-2, were not changed. On the contrary, the PGFS mRNA was down-regulated in the obstructed colon. 2. PGE2, but not PGF2 α, was significantly increased in the colonic muscularis externae in obstruction. The PGE2 level increased to 4577±1249 pg/mg at day 3 of obstruction, compared to 1264±259 in sham (n=6, p,0.05). The PGF2α level was 5718±910 pg /mg in obstruction compared to 6550±2178 pg/mg in the sham (n=5, p.0.05). 3. Direct stretch of rat colonic circular SMCs in vitro significantly up-regulated the mPGES-1 mRNA, but down-regulated that of PGFS. After stretch for 3 hrs, the mRNA levels of PGES and PGFS changed by 2.61±0.42 fold and 0.82±0.03 fold, respectively (n = 4 or 5, p,0.05). 4. In colonic inflammation, both PGE2 and PGF2α were significantly increased in the colonic smooth muscle (5.2(±1.5)-fold and 4.7(±1.3)-fold of control, respectively, p,0.05, n = 3). 5. Rat colonic circular muscle contractility was inhibited by exogenous PGE2 (10-9 ~10-6 M), but enhanced by PGF2 α (10-9 ~10-6 M) in a concentration-dependent manner (n = 4). Conclusions: Genes involved in the COX pathway of arachidonic acid metabolism are highly mechanosensitive in colonic SMCs, and play a critical role in motility function. Mechano-regulation of prostaglandin synthases accounts for increased PGE2 and unchanged PGF2 α in bowel obstruction, a pathological feature different from inflammation in which both PGE2 and PGF2 α are increased.

Sa2065 Purinergic Pathway Is the Major Mechanism of Inhibitory Effect of Motilitone on the Rat Gastric Fundus Relaxation

Previous studies found that mechanical stretch in bowel obstruction markedly induced gene expression of COX-2, but not COX-1, in colonic smooth muscle cells (SMCs). The aims of the present study were to determine whether genes encoding individual prostaglandin synthases are mechanically responsive, and whether the composition of prostaglandins resulting from obstruction differs from that in inflammation. Methods: Partial colon obstruction was induced with a silicon band implanted surgically in the distal colon of male SpragueDawley rats. Static mechanical stretch (18% elongation) was mimicked in vitro in the culture of rat colonic circular SMCs with a Flexercell FX-4000 System. Rat colon inflammation was induced by manipulation of the colonic surface with wet cotton applicators. Results: 1. Quantitative RT-PCR found that the expression of PGDS and PGIS genes was not significantly changed on day 3 of obstruction. However, the membrane bound PGES-1 (mPGES-1) mRNA was significantly up-regulated in the obstructed segment, whereas mRNAs for other two types of PGES, cytosolic PGES and mPGES-2, were not changed. On the contrary, the PGFS mRNA was down-regulated in the obstructed colon. 2. PGE2, but not PGF2 α, was significantly increased in the colonic muscularis externae in obstruction. The PGE2 level increased to 4577±1249 pg/mg at day 3 of obstruction, compared to 1264±259 in sham (n=6, p,0.05). The PGF2α level was 5718±910 pg /mg in obstruction compared to 6550±2178 pg/mg in the sham (n=5, p.0.05). 3. Direct stretch of rat colonic circular SMCs in vitro significantly up-regulated the mPGES-1 mRNA, but down-regulated that of PGFS. After stretch for 3 hrs, the mRNA levels of PGES and PGFS changed by 2.61±0.42 fold and 0.82±0.03 fold, respectively (n = 4 or 5, p,0.05). 4. In colonic inflammation, both PGE2 and PGF2α were significantly increased in the colonic smooth muscle (5.2(±1.5)-fold and 4.7(±1.3)-fold of control, respectively, p,0.05, n = 3). 5. Rat colonic circular muscle contractility was inhibited by exogenous PGE2 (10-9 ~10-6 M), but enhanced by PGF2 α (10-9 ~10-6 M) in a concentration-dependent manner (n = 4). Conclusions: Genes involved in the COX pathway of arachidonic acid metabolism are highly mechanosensitive in colonic SMCs, and play a critical role in motility function. Mechano-regulation of prostaglandin synthases accounts for increased PGE2 and unchanged PGF2 α in bowel obstruction, a pathological feature different from inflammation in which both PGE2 and PGF2 α are increased.

Su2080 IL-17 Enhances Carbachol-Induced CA2+ Influx and Contraction of Human Colonic Smooth Muscle Cells

Su2080 IL-17 Enhances Carbachol-Induced CA2+ Influx and Contraction of Human Colonic Smooth Muscle Cells

254 Advanced Glycation End Products Cause Colonic Smooth Muscle Cells Hypertrophy in the Diabetic Rat via p38 MAPK Pathway

254 Advanced Glycation End Products Cause Colonic Smooth Muscle Cells Hypertrophy in the Diabetic Rat via p38 MAPK Pathway

Altered Expression Pattern of Molecular Factors Involved in Colonic Smooth Muscle Functions: An Immunohistochemical Study in Patients with Diverticular Disease

BackgroundThe pathogenesis of diverticular disease (DD) is thought to result from complex interactions among dietary habits, genetic factors and coexistence of other bowel abnormalities. These conditions lead to alterations in colonic pressure and motility, facilitating the formation of diverticula. Although electrophysiological studies on smooth muscle cells (SMCs) have investigated colonic motor dysfunctions, scarce attention has been paid to their molecular abnormalities, and data on SMCs in DD are lacking. Accordingly, the main purpose of this study was to evaluate the expression patterns of molecular factors involved in the contractile functions of SMCs in the tunica muscularis of colonic specimens from patients with DD.Methods and FindingsBy means of immunohistochemistry and image analysis, we examined the expression of Cx26 and Cx43, which are prominent components of gap junctions in human colonic SMCs, as well as pS368-Cx43, PKCps, RhoA and αSMA, all known to regulate the functions of gap junctions and the contractile activity of SMCs.The immunohistochemical analysis revealed significant abnormalities in DD samples, concerning both the expression and distribution patterns of most of the investigated molecular factors.ConclusionThis study demonstrates, for the first time, that an altered pattern of factors involved in SMC contractility is present at level of the tunica muscularis of DD patients. Moreover, considering that our analysis was conducted on colonic tissues not directly affected by diverticular lesions or inflammatory reactions, it is conceivable that these molecular alterations may precede and predispose to the formation of diverticula, rather than being mere consequences of the disease.

Actions of Hydrogen Sulfide and ATP-Sensitive Potassium Channels on Colonic Hypermotility in a Rat Model of Chronic Stress

ObjectiveTo investigate the potential role of hydrogen sulphide (H2S) and ATP-sensitive potassium (KATP) channels in chronic stress-induced colonic hypermotility.MethodsMale Wistar rats were submitted daily to 1 h of water avoidance stress (WAS) or sham WAS (SWAS) for 10 consecutive days. Organ bath recordings, H2S production, immunohistochemistry and western blotting were performed on rat colonic samples to investigate the role of endogenous H2S in repeated WAS-induced hypermotility. Organ bath recordings and western blotting were used to detect the role of KATP channels in repeated WAS.ResultsRepeated WAS increased the number of fecal pellets per hour and the area under the curve of the spontaneous contractions of colonic strips, and decreased the endogenous production of H2S and the expression of H2S-producing enzymes in the colon devoid of mucosa and submucosa. Inhibitors of H2S-producing enzymes increased the contractile activity of colonic strips in the SWAS rats. NaHS concentration-dependently inhibited the spontaneous contractions of the strips and the NaHS IC50 for the WAS rats was significantly lower than that for the SWAS rats. The inhibitory effect of NaHS was significantly reduced by glybenclamide. Repeated WAS treatment resulted in up-regulation of Kir6.1 and SUR2B of KATP channels in the colon devoid of mucosa and submucosa.ConclusionThe colonic hypermotility induced by repeated WAS may be associated with the decreased production of endogenous H2S. The increased expression of the subunits of KATP channels in colonic smooth muscle cells may be a defensive response to repeated WAS. H2S donor may have potential clinical utility in treating chronic stress- induced colonic hypermotility.

Effect of endogenous insulin-like growth factor and stem cell factor on diabetic colonic dysmotility

To investigate whether the reduction of stem cell factor (SCF) is mediated by decreased endogenous insulin-like growth factor (IGF)-1 in diabetic rat colon smooth muscle. Sixteen Sprague-Dawley rats were randomly divided into two groups: control group and streptozotocin-induced diabetic group. After 8 wk of streptozotocin administration, colonic motility function and contractility of circular muscle strips were measured. The expression of endogenous IGF-1 and SCF was tested in colonic tissues. Colonic smooth muscle cells were cultured from normal adult rats. IGF-1 siRNA transfection was used to investigate whether SCF expression was affected by endogenous IGF-1 expression in smooth muscle cells, and IGF-1 induced SCF expression effects were studied. The effect of high glucose on the expression of endogenous IGF-1 and SCF was also investigated. Diabetic rats showed prolonged colonic transit time (252 ± 16 min vs 168 ± 9 min, P < 0.01) and weakness of circular muscle contraction (0.81 ± 0.09 g vs 2.48 ± 0.23 g, P < 0.01) compared with the control group. Endogenous IGF-1 and SCF protein expression was significantly reduced in the diabetic colonic muscle tissues. IGF-1 and SCF mRNA expression also showed a paralleled reduction in diabetic rats. In the IGF-1 siRNA transfected smooth muscle cells, SCF mRNA and protein expression was significantly decreased. IGF-1 could induce SCF expression in a concentration and time-dependent manner, mainly through the extracellular-signal-regulated kinase 1/2 signal pathway. High glucose inhibited endogenous IGF-1 and SCF expression and the addition of IGF-1 to the medium reversed the SCF expression. Myopathy may resolve in colonic motility dysfunction in diabetic rats. Deficiency of endogenous IGF-1 in colonic smooth muscle cells leads to reduction of SCF expression.

Cell culture retains contractile phenotype but epigenetically modulates cell-signaling proteins of excitation-contraction coupling in colon smooth muscle cells.

Smooth muscle cell cultures are used frequently to investigate the cellular mechanisms of contraction. We tested the hypothesis that cell culture alters the expression of select cell-signaling proteins of excitation-contraction coupling in colon smooth muscle cells without altering the contractile phenotype. We used muscularis externa (ME) tissues, freshly dispersed cells (FC), primary cell cultures (PC), and resuspensions of cell cultures (RC). Colon smooth muscle cells retained their phenotype in all states. We investigated expression of 10 cell-signaling proteins of excitation-contraction coupling in all four types of tissue. Expression of all these proteins did not differ between ME and FC (P > 0.05). However, expression of the α(1C)-subunit of Ca(v)1.2b, myosin light chain kinase, myosin phosphatase target subunit 1, and 17-kDa C kinase-potentiated protein phosphatase-1 inhibitor (CPI-17) decreased in PC and RC vs. ME and FC (all P < 0.05). Expression of Gα(i3), serine/threonine protein phosphatase-1 β-catalytic subunit, and Rho kinase 1 increased in PC and RC vs. ME and FC (all P < 0.05). Cell culture and resuspension downregulated expression of α-actin and calponin, but not myosin heavy chain. The net effect of these molecular changes was suppression of cell reactivity to ACh in RC vs. FC. Overexpression of CPI-17 in PC partially reversed the suppression of contractility in resuspended cells. Methylation-specific PCR showed increased methylation of the Cpi-17 gene promoter in PC vs. ME (P < 0.05). We concluded that smooth muscle cells retain their contractile phenotype in culture. However, reactivity to ACh declines because of altered expression of specific cell-signaling proteins involved in excitation-contraction coupling. DNA methylation of the Cpi-17 promoter may contribute to its gene suppression.

Hydrogen Sulfide as an Allosteric Modulator of ATP-Sensitive Potassium Channels in Colonic Inflammation

The ATP-sensitive potassium channel (K(ATP)) in mouse colonic smooth muscle cell is a complex containing a pore-forming subunit (Kir6.1) and a sulfonylurea receptor subunit (SUR2B). These channels contribute to the cellular excitability of smooth muscle cells and hence regulate the motility patterns in the colon. Whole-cell voltage-clamp techniques were used to study the alterations in K(ATP) channels in smooth muscle cells in experimental colitis. Colonic inflammation was induced in BALB/C mice after intracolonic administration of trinitrobenzene sulfonic acid. K(ATP) currents were measured at a holding potential of -60 mV in high K(+) external solution. The concentration response to levcromakalim (LEVC), a K(ATP) channel opener, was significantly shifted to the left in the inflamed smooth-muscle cells. Both the potency and maximal currents induced by LEVC were enhanced in inflammation. The EC(50) values in control were 6259 nM (n = 10) and 422 nM (n = 8) in inflamed colon, and the maximal currents were 9.9 ± 0.71 pA/pF (60 μM) in control and 39.7 ± 8.8 pA/pF (3 μM) after inflammation. As was seen with LEVC, the potency and efficacy of sodium hydrogen sulfide (NaHS) (10-1000 μM) on K(ATP) currents were significantly greater in inflamed colon compared with controls. In control cells, pretreatment with 100 µM NaHS shifted the EC(50) for LEV-induced currents from 2838 (n = 6) to 154 (n = 8) nM. Sulfhydration of sulfonylurea receptor 2B (SUR2B) was induced by NaHS and colonic inflammation. These data suggest that sulfhydration of SUR2B induces allosteric modulation of K(ATP) currents in colonic inflammation.

Antioxidants counteract lipopolysaccharide-triggered alterations of human colonic smooth muscle cells

Gut dysmotility develops in individuals during and after recovering from infective acute gastroenteritis and it is apparently due to a direct effect of circulating lipopolysaccharides (LPS). This is an endotoxin with a prooxidant activity derived from gram-negative bacteria. Due to the lack of human models available so far, the mechanisms underlying LPS-induced gut dysmotility are, however, poorly investigated. In the present work long-term effects of LPS and their reversibility have been assessed by means of different analytical cytology methods on pure primary cultures of human colonic smooth muscle cells. We found that LPS triggered the following alterations: (i) a redox imbalance with profound changes of contractile microfilament network, and (ii) the induction of cell cycle progression with dedifferentiation from a contractile to a synthetic phenotype. These alterations persisted also after LPS removal. Importantly, two unrelated antioxidants, alpha-tocopherol and N-acetylcysteine, were able to reverse the cytopathic effects of LPS and to restore normal muscle cell function. The present data indicate that LPS is capable of triggering a persistent and long-term response that could contribute to muscle dysfunction occurring after an infective and related inflammatory burst and suggest a reappraisal of antioxidants in the management of postinfective motor disorders of the gut.

Microbiota, Innate Immune System, and Gastrointestinal Muscle

To test the activities of culture-extracted or commercially available toll-like receptors (TLRs) ligands to establish their direct impact on target gastrointestinal motor cells. Short-term and long-term effects of Shigella flexneri M90T and Escherichia coli K-2 strains-extracted lipopolysaccharides (LPS), commercially highly purified LPS (E. coli O111:B4 and EH100), and Pam2CSK4 and Pam3CSK4, which bind TLR2/6 and TLR1/2 heterodimers, respectively, have been assessed on pure primary cultures of colonic human smooth muscle cells (HSMC). Pathogenic Shigella-LPS and nonpathogenic E. coli K-2-LPS induced a time-dependent decrease of resting cell length and acetylcholine-induced contraction, with both alterations occurring rapidly and being more pronounced in response to the former. However, their effects differed, prolonging HSMC exposure with Shigella-LPS effects maintained throughout the 4 hours of observation compared with E. coli K-2-LPS, which disappeared after 60 minutes of incubation. Similar differences in magnitude and time dependency of myogenic effects were observed between pure TLR4 and TLR2/1 or TLR2/6 ligands. The specific activation of TLR4 with LPS from pathogen or nonpathogen E. coli, O111:B4 and EH100, respectively, induced smooth muscle alterations that progressively increased, prolonging incubation, whereas TLR2 ligands induced short-term alterations, of a lesser magnitude, which decreased over time. The real-time polymerase chain reaction analysis showed that HSMC express mRNA for TLR1, 2, 4, and 6, substantiating a direct effect of TLR ligands on human colonic smooth muscle. This study highlights that bacterial products can directly affect gastrointestinal motility and that TLRs subtypes may differ in their cellular activity.