Contraction Of Circular Smooth Muscle Research Articles

Characterization of the alpha1-adrenoceptor subtype mediating contractions of the pig internal anal sphincter.

The internal anal sphincter has been shown to contract in response to alpha1-adrenoceptor stimulation and therefore alpha1-adrenoceptor agonists may be useful in treating faecal incontinence. This study characterizes the alpha1-adrenoceptor subtype responsible for mediating contraction of the internal anal sphincter of the pig. The potency of agonists and the affinities of several receptor subtype selective antagonists were determined on smooth muscle strips for the pig internal anal sphincter. Cumulative concentration-response curves were performed using phenylephrine and noradrenaline. The potency of the alpha1A-adrenoceptor selective agonist A61603 (pEC50=7.79+/-0.04) was 158-fold greater than that for noradrenaline (pEC50=5.59+/-0.02). Phenylephrine (pEC50=5.99+/-0.05) was 2.5-fold more potent than noradrenaline. The alpha1D-adrenoceptor selective antagonist BMY7378 caused rightward shifts of the concentration-response curves to phenylephrine and noradrenaline, yielding low affinity estimates of 6.59+/-0.15 and 6.33+/-0.13, respectively. Relatively high affinity estimates were obtained for the alpha1A-adrenoceptor selective antagonists, RS100329 (9.01+/-0.14 and 9.06+/-0.22 with phenylephrine and noradrenaline, respectively) and 5-methylurapidil (8.51+/-0.10 and 8.31+/-0.10, respectively). Prazosin antagonized responses of the sphincter to phenylephrine and noradrenaline, yielding mean affinity estimates of 8.58+/-0.10 and 8.15+/-0.08, respectively. The Schild slope for prazosin with phenylephrine was equal to unity (1.01+/-0.24), however the Schild slope using noradrenaline was significantly less than unity (0.50+/-0.11, P<0.05). The results suggest that contraction of circular smooth muscle from the pig internal anal sphincter is mediated via a population of adrenoceptors with the pharmacological characteristics of the alpha1A/L-adrenoceptor, most probably the alpha1L-adrenoceptor form of this receptor.

Estrous cycle‐dependent differences in responsiveness to prostaglandins and contractile agents in sheep (Ovis aries) cervical smooth muscle

We investigated the influence of the phase of the estrous cycle on mechanical responses elicited in sheep cervix by potassium chloride (KCl), acetylcholine chloride (ACh), prostaglandin F2 alpha (PGF2 alpha) and prostaglandin E1 (PGE1). The cervix of adult ewes (n = 48) were classified according to the presence or absence of corpora lutea (luteal or follicular phase, respectively). Muscle strips of the circular and longitudinal layers were prepared in an organ bath and coupled to an isometric force transducer. Concentration-response curves were obtained noncumulatively. KCl and ACh produced concentration-dependent contractions in all preparations in both phases of the estrous cycle. However, maximum effect, EC50 and slope values of KCl and ACh were not significantly different between muscle layers, as well as between the phases of the estrous cycle. The prostanoid, PGF2 alpha, produced a significant reduction in the amplitude of spontaneous contractions for all preparations. The depressant effect of PGF2 alpha on spontaneous contractions of circular smooth muscle was significantly greater during the follicular than the luteal phase, whilst the depressant effect of PGF2 alpha on the longitudinal layer did not differ between phases of the estrous cycle. PGE1 significantly reduced the amplitude of spontaneous contractions on circular but not on longitudinal preparations. In conclusion, we have characterized with in vitro preparations of circular and longitudinal muscle layers of ewes during the follicular and luteal phases of the estrous cycle, the parameters of the K- and ACh-induced contractions on cervix and the efficacy of PGF2 alpha and PGE1 on inhibition spontaneous contractile activity.

Development and physiology of gastric dilation air sacculitis in Chinook salmon, Oncorhynchus tshawytscha (Walbaum)

The syndrome known as gastric dilation air sacculitis (GDAS) has previously been shown to affect Chinook salmon, Oncorhynchus tshawytscha, in seawater (SW) aquaculture. Feed and osmoregulatory stress have been implicated as potential epidemiological co-factors. The development and physiology of GDAS was investigated in SW and freshwater (FW) adapted smolts. Diet A (low-cohesion pellets) and diet B (high-cohesion pellets) were fed to both FW- and SW-adapted fish. GDAS was induced only in the SW trial on feeding diet A. Stimulated gastro-intestinal (GI) smooth muscle contractility, and fluid transport by the pyloric caeca were different in GDAS-affected fish, which also showed osmoregulatory dysfunction. Cardiac stomach (CS) smooth muscle contractility in response to acetylcholine and potassium chloride (KCl) was significantly reduced in fish fed diet A relative to controls from weeks 3-5. In contrast, maximal pyloric sphincter (PS) circular smooth muscle contraction in response to KCl was significantly elevated in fish fed diet A in weeks 4 and 5. Serum osmolality was elevated in GDAS-affected fish from week 2 of the SW trial. Fluid transport from the mucosal to serosal surface of isolated pyloric caeca was significantly reduced in weeks 3, 4 and 5 in SW fish fed diet A. Gastric evacuation from the stomach of healthy fish was shown to be significantly different when diets of low- and high-cohesion were fed. The results are consistent with the intestinal brake playing a role in the development of the disease.

Gastroesophageal Reflux Disease–Associated Esophagitis Induces Endogenous Cytokine Production Leading to Motor Abnormalities

Gastroesophageal reflux disease is a condition frequently associated with esophagitis and motor abnormalities. Recent evidence suggests that proinflammatory cytokines, such as interleukin (IL)-1beta and IL-6, may be implicated because they reduce esophageal muscle contractility, but these results derive from in vitro or animal models of esophagitis. This study used human esophageal cells and tissues to identify the cellular source of cytokines in human esophagitis investigate whether cytokines can be induced by gastric refluxate, and examine whether esophageal tissue- or cell-derived mediators affect muscle contractility. Endoscopic mucosal biopsy specimens were obtained from patients with and without esophagitis, organ-cultured, and undernatants were assessed for cytokine content. The cytokine profile of esophageal epithelial, fibroblast, and muscle cells was analyzed, and esophageal mucosa and cell products were tested in an esophageal circular muscle contraction assay. The mucosa of esophagitis patients produced significantly greater amounts of IL-1beta and IL-6 compared with those of control patients. Cultured esophageal epithelial cells produced IL-6, as did fibroblasts and muscle cells. Epithelial cells exposed to buffered, but not denatured, gastric juice produced IL-6. Undernatants of mucosal biopsy cultures from esophagitis patients reduced esophageal muscle contraction, as did supernatants from esophageal epithelial cell cultures. The human esophagus produces cytokines capable of reducing contractility of esophageal muscle cells. Exposure to gastric juice is sufficient to stimulate esophageal epithelial cells to produce IL-6, a cytokine able to alter esophageal contractility. These results indicate that classic cytokines are important mediators of the motor disturbances associated with human esophageal inflammation.

Alpha1A/L‐adrenoceptors mediate contraction of the circular smooth muscle of the pig urethra

Sympathetically mediated urethral tone is essential for the maintenance of continence and involves the activation of postjunctional alpha(1)-adrenoceptors. This study characterizes the alpha(1)-adrenoceptor subtypes responsible for mediating contraction of the urethral circular smooth muscle of the pig. The potency order of a number of agonists and the affinities of several receptor selective antagonists were determined on pig-isolated circular smooth muscle strips in the presence of cocaine (1 microm) and corticosterone (10 microm) to inhibit amine uptake and propranolol (1 microm) to antagonize beta-adrenoceptors. The potency order for agonists was N-[5-(4,5-dihydro-1H-imidazol-2yl)-2-hydroxy-5,6,7,8-tetrahydronaphthalen-1-yl]methanesulphonamide (A61603) > noradrenaline = phenylephrine = M6434 > methoxamine with pEC(50) values of 7.3, 5.8, 5.7, 5.6 and 5.0 respectively. 4 The alpha(1D)-adrenoceptor-selective antagonist 8-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-8-azaspiro[4,5]decane-7,9-dione (BMY7378) caused rightward shifts of the concentration-response curves to noradrenaline, yielding a low affinity estimate (6.6) for the urethral receptor. The alpha(1A)-adrenoceptor-selective antagonists, RS100329 and 5-methylurapidil, gave relatively high affinity estimates (9.6 and 8.8 respectively) for this receptor. All three antagonists produced Schild plots with slopes close to unity but did reduce maximum responses at higher concentrations. Prazosin antagonized responses of the urethra to noradrenaline, yielding a mean affinity estimate of 9.0. Although the Schild plot for prazosin again had a slope of unity, this drug also reduced maximum responses to noradrenaline at all concentrations examined (10-100 nm). N-[2-(2-cyclopropylmethoxyphenoxy)ethyl]-5-chloro-alpha,alpha-dimethyl-1H-indole-3-ethanamide (RS17053), which discriminates between responses mediated via alpha(1A) (high affinity) and alpha(1L)-adrenoceptors (low affinity) at concentrations up to 3 microm, failed to antagonize responses of the urethra. 5 These results suggest that contraction of urethral circular smooth muscle in the pig is mediated via a single population of adrenoceptors with the pharmacological characteristics of the alpha(1A/L)-adrenoceptor, most probably the alpha(1L)-adrenoceptor.

NK2 Receptor-Mediated Spontaneous Phasic Contractions in Normal and Ulcerative Colitis Human Sigmoid Colon

Human colonic circular muscle produces spontaneous phasic contractions that are reduced in ulcerative colitis. How the spontaneous phasic contractions develop and why they decrease in ulcerative colitis are not known. We found that spontaneous phasic contractions of normal sigmoid circular muscle strips were significantly reduced by 90-min incubation with tetrodotoxin (10(-5) M), which blocked neurokinin A release in basal conditions and in response to electrical stimulation. In addition, spontaneous contraction of human sigmoid colon was significantly decreased by the NK2 receptor antagonists MEN10376 (Asp-Tyr-D-Trp-Val-D-Trp-D-Trp-Lys-NH2) and NK2ra (Bz-Ala-Ala-D-Trp-Phe-D-pro-Pro-Nle-NH2) but not by atropine or by the NK1 antagonist FK888 (N2-[(4R)-4-hydroxyl-1-(1-methyl-1H-indol-3-yl)carbonyl-l-prolyl]-N-methyl-N-phenylmethyl-3-(2-naphthyl)-l-alaninamide), suggesting that NK2 receptors are involved in their development. The spontaneous phasic contractions were abolished by thapsigargin and cyclopiazonic acid and significantly decreased by the protein kinase C inhibitor chelerythrine and by the calmodulin inhibitor CGS9343B (1,3-dihydro-1-[1-[(4-methyl-4H,6H-pyrrolo[1,2-a]-[4,1]-benzoxazepin-4-yl)methyl]-4-piperidinyl]-2H-benzimidazol-2-one (1:1) maleate), suggesting that spontaneous phasic contractions may be mediated by Ca2+ release from intracellular stores and by a protein kinase C- and calmodulin-dependent pathway. In strips from patients with ulcerative colitis, spontaneous contractions were significantly reduced, and this reduction was partially restored by the hydrogen peroxide scavenger catalase. Neurokinin A release, however, was not affected. We conclude that spontaneous phasic contractions of human sigmoid circular smooth muscle may be mediated by activation of NK2 receptors, calcium release from intracellular stores, and activation of calmodulin and protein kinase C. In ulcerative colitis patients, spontaneous phasic contractions are decreased, and this decrease may be in part due to overproduction of hydrogen peroxide affecting sigmoid circular muscle.

Muscle Shortening Along the Normal Esophagus During Swallowing

Longitudinal shortening of the esophagus during peristaltic contraction has been previously analyzed globally using spaced mucosal clips. This method gives a relatively crude measurement. In this study, local longitudinal shortening (LLS) was evaluated using simultaneous high-resolution endoluminal ultrasound (HREUS) and manometry based on basic principles of muscle mechanics. We sought to determine if there are regional differences in LLS of the esophageal muscle during swallow-induced peristaltic contraction and evaluate shortening of the circular smooth muscle (CSM) and longitudinal smooth muscle (LSM) of the esophagus. Twenty normal subjects underwent simultaneous HREUS/manometry at 4 levels (5, 10, 15, and 20 cm above the upper border of the lower esophageal sphincter [LES] high-pressure zone) in the esophagus with 5-mL swallows of water. Ultrasound images were recorded with synchronized manometric pressure data. The images were digitized and the cross-sectional surface area (CSA) of the LSM, CSM, and total muscle (TM) were measured at baseline (at rest) and at peak intraluminal pressure (implying peak CSM contraction) during swallowing. LLS was calculated for the CSM and LSM using the principle of mass conservation, whereby the change in CSA relative to the resting CSA is quantitatively equal to the relative change in length of a local longitudinal muscle segment.CSM, LSM, and TM all shortened longitudinally, with the circular muscle shortening more than the longitudinal muscle, LLS of the CSM and TM layers at 5 cm above the LES was significantly greater than at 20 cm (CSM: 30% difference, P < .001; TM: 18% difference, P < .05). The greater shortening of LSM at 5 versus 20 cm was found not to be statistically significant (11% difference, P > .05). Peak intraluminal pressure strongly correlated with peak muscle thickness of all layers at all levels (r = 0.96-0.98).LLS increases from the proximal to the distal esophagus during bolus transport. CSM and LSM both shorten longitudinally, with CSM shortening more than LSM. The increase in LLS increases the efficiency of peristaltic contraction and likely contributes to the axial displacement of the LES preceding hiatal opening and esophageal emptying.

Mechanisms mediating cholinergic antral circular smooth muscle contraction in rats

To investigate the pathway (s) mediating rat antral circular smooth muscle contractile responses to the cholinomimetic agent, bethanechol and the subtypes of muscarinic receptors mediating the cholinergic contraction. Circular smooth muscle strips from the antrum of Sprague-Dawley rats were mounted in muscle baths in Krebs buffer. Isometric tension was recorded. Cumulative concentration-response curves were obtained for (+)-cis-dioxolane (cD), a nonspecific muscarinic agonist, at 10(-8)-10(-4) mol/L, in the presence of tetrodotoxin (TTX, 10(-7) mol/L). Results were normalized to cross sectional area. A repeat concentration-response curve was obtained after incubation of the muscle for 90 min with antagonists for M1 (pirenzepine), M2 (methoctramine) and M3 (darifenacin) muscarinic receptor subtypes. The sensitivity to PTX was tested by the ip injection of 100 mg/kg of PTX 5 d before the experiment. The antral circular smooth muscles were removed from PTX-treated and non-treated rats as strips and dispersed smooth muscle cells to identify whether PTX-linked pathway mediated the contractility to bethanechol. A dose-dependent contractile response observed with bethanechol, was not affected by TTX. The pretreatment of rats with pertussis toxin decreased the contraction induced by bethanechol. Lack of calcium as well as the presence of the L-type calcium channel blocker, nifedipine, also inhibited the cholinergic contraction, with a reduction in response from 2.5+/-0.4 g/mm2 to 1.2+/-0.4 g/mm(2) (P<0.05). The dose-response curves were shifted to the right by muscarinic antagonists in the following order of affinity: darifenacin (M(3))>methocramine (M(2)) >pirenzepine (M(1)). The muscarinic receptors-dependent contraction of rat antral circular smooth muscles was linked to the signal transduction pathway(s) involving pertussis-toxin sensitive GTP-binding proteins and to extracellular calcium via L-type voltage gated calcium channels. The presence of the residual contractile response after the treatment with nifedipine, suggests that an additional pathway could mediate the cholinergic contraction. The involvement of more than one muscarinic receptor (functionally predominant type 3 over type 2) also suggests more than one pathway mediating the cholinergic contraction in rat antrum.

Tachykinins mediate non-adrenergic, non-cholinergic excitatory neurotransmission to the hamster ileum via NK1 and NK2 receptors

The present study was designed to investigate Substance P (SP) and a related tachykinin, Neurokinin A (NKA), contributions to the excitatory neurotransmission to the circular smooth muscle of the hamster ileum. In the presence of atropine (0.5 μM), guanethidine (3 μM) and N G-nitro-L-arginine methyl ester (L-NAME) (200 μM), electrical field stimulation (EFS) evoked a non-adrenergic, non-cholinergic (NANC) excitatory junction potential (EJP) and contraction of circular smooth muscle. Applications of SP and NKA produced depolarizing and contractile responses in a concentration-dependent fashion. The EJP and contraction were almost abolished by the non-specific tachykininergic antagonist, spantide (3 μM). Application of SP antagonist, L-732,138, (1 μM) markedly inhibited EJP (82.5%) and contraction (68.9%) and completely blocked excitatory responses produced by exogenous application of SP. While application of NKA antagonist, SR48968 (1 μM) completely blocked the depolarising and contractile responses to NKA, it only slightly inhibited those to EFS (17.2% and 31.4% respectively).These results provide evidence that, in the circular muscle of hamster ileum, endogenous tachykinins are the main NANC excitatory neurotransmitters and their action is mediated by both NK1 and NK2 receptors.

MAPK mediates PKC-dependent contraction of cat esophageal and lower esophageal sphincter circular smooth muscle.

Esophageal (ESO) circular muscle contraction and lower esophageal sphincter (LES) tone are PKC dependent. Because MAPKs may be involved in PKC-dependent contraction, we examined ERK1/ERK2 and p38 MAPKs in ESO and LES. In permeabilized LES muscle cells, ERK1/2 antibodies reduced 1,2-dioctanoylglycerol (DG)- and threshold ACh-induced contraction, which are PKC dependent, but not maximal ACh, which is calmodulin dependent. LES tone was reduced by the ERK1/2 kinase inhibitor PD-98059 and by the p38 MAPK inhibitor SB-203580. In permeable ESO cells, ACh contraction was reduced by ERK1/ERK2 and p38 MAPK antibodies and by PD-98059 and SB-203580. ACh increased MAPK activity and phosphorylation of MAPK and of p38 MAPK. The 27-kDa heat shock protein (HSP27) antibodies reduced ACh contraction. HSP27 and p38 MAPK antibodies together caused no greater inhibition than either one alone. p38 MAPK and HSP27 coprecipitated after ACh stimulation, suggesting that HSP27 is linked to p38 MAPK. These data suggest that PKC-dependent contraction in ESO and LES is mediated by the following two distinct MAPK pathways: ERK1/2 and HSP27-linked p38 MAPK.

Decrease in activity of smooth muscle L-type Ca2+ channels and its reversal by NF-kappaB inhibitors in Crohn's colitis model.

We investigated the mechanisms of dysmotility of the colonic circular muscle of the Crohn's disease rat model. Contractions induced by KCl, carbachol, and Bay K 8644 were decreased in circular smooth muscles isolated from 2,4,6-trinitrobenzenesulfonic acid (TNBS)-induced colitis rat colon. However, the absolute force and Ca2+ sensitivity of contractile proteins were not affected as assessed in alpha-toxin permeabilized smooth muscle. The current density of the L-type Ca2+ channel in circular smooth muscle cells was significantly decreased in the TNBS-treated colonic cells. However, expressions of the L-type Ca2+ channel mRNA and protein did not differ between control and TNBS-treated preparations. Pretreatment with the NF-kappaB inhibitors pyrrolidinedithiocarbamate and sulfasalazine partially recovered the decreased contractility and current density of the L-type Ca2+ channel by TNBS treatment. These results suggest that the decrease in the contraction of circular smooth muscle isolated from TNBS-induced colitis rat colon, which may be related to gut dysmotility in Crohn's disease, is attributable to the decreased activity of the L-type Ca2+ channel. The dysfunction of the L-type Ca2+ channel may be mediated by NF-kappaB-dependent pathways.

PGF(2alpha)-induced contraction of cat esophageal and lower esophageal sphincter circular smooth muscle.

Lower esophageal sphincter (LES) tone depends on PGF(2alpha) and thromboxane A(2) acting on receptors linked to G(i3) and G(q) to activate phospholipases and produce second messengers resulting in muscle contraction. We therefore examined PGF(2alpha) signal transduction in circular smooth muscle cells isolated by enzymatic digestion from cat esophagus (Eso) and LES. In Eso, PGF(2alpha)-induced contraction was inhibited by antibodies against the alpha-subunit of G(13) and the monomeric G proteins RhoA and ADP-ribosylation factor (ARF)1 and by the C3 exoenzyme of Clostridium botulinum. A [(35)S]GTPgammaS-binding assay confirmed that G(13), RhoA, and ARF1 were activated by PGF(2alpha). Contraction of Eso was reduced by propranolol, a phospholipase D (PLD) pathway inhibitor and by chelerythrine, a PKC inhibitor. In LES, PGF(2alpha)-induced contraction was inhibited by antibodies against the alpha-subunit of G(q) and G(i3), and a [(35)S]GTPgammaS-binding assay confirmed that G(q) and G(i3) were activated by PGF(2alpha). PGF(2alpha)-induced contraction of LES was reduced by U-73122 and D609 and unaffected by propranolol. At low PGF(2alpha) concentration, contraction was blocked by chelerythrine, whereas at high concentration, contraction was blocked by chelerythrine and CGS9343B. Thus, in Eso, PGF(2alpha) activates a PLD- and protein kinase C (PKC)-dependent pathway through G(13), RhoA, and ARF1. In LES, PGF(2alpha) receptors are coupled to G(q) and G(i3), activating phosphatidylinositol- and phosphatidylcholine-specific phospholipase C. At low concentrations, PGF(2alpha) activates PKC. At high concentration, it activates both a PKC- and a calmodulin-dependent pathway.

The Role of M2 Muscarinic Receptor Subtypes Mediating Contraction of the Circular and Longitudinal Smooth Muscle of the Pig Proximal Urethra

The Role of M2 Muscarinic Receptor Subtypes Mediating Contraction of the Circular and Longitudinal Smooth Muscle of the Pig Proximal Urethra

Abnormal motility in patients with ulcerative colitis: the role of inflammatory cytokines.

Interleukin 1 beta (IL-1 beta) levels are elevated in the colonic mucosa of patients with ulcerative colitis (UC). We propose that IL-1 beta may also be elevated in the circular muscle layer of the colon and may be partially responsible for the motility dysfunction observed in patients with UC. Cohort analytic study. Research laboratory in a tertiary academic medical center. Normal smooth muscle was obtained from the disease-free margins of human sigmoid colon specimens resected from patients with cancer and compared with specimens from patients with UC. An enzyme-linked immunosorbent assay was used to measure IL-l beta. Standard muscle chambers were used to measure force changes. Single muscle cells were isolated by enzymatic digestion, and cell shortening in response to neurokinin A (NKA) and thapsigargin was measured under a microscope. Cytosolic Ca(2+) (calcium) concentrations were measured by standard techniques. Effects of IL-1 beta on smooth muscle function in normal and UC colons. In patients with UC, IL-1 beta was elevated in the muscularis propria, and sigmoid circular smooth muscle contractions in response to NKA and thapsigargin were significantly reduced. In fura-2-loaded cells from patients with UC, the NKA-induced Ca(2+) signal was also significantly reduced in Ca(2+)-free medium, indicating the reduced intracellular Ca(2+) stores after UC. Exposure of normal cells to IL-1 beta mimicked the changes observed in patients with UC. An IL-1 beta-induced reduction in contraction and release of intracellular Ca(2+) in response to NKA was partially restored by the hydrogen peroxide scavenger catalase. In patients with UC, IL-1 beta was increased in colonic circular muscles and may contribute to motor dysfunction after UC through production of hydrogen peroxide.

Effect of short-chain fatty acids on contraction of smooth muscle in the canine colon.

To determine effects of short-chain fatty acids (SCFA) on canine colonic smooth muscle. Colonic tissue obtained from 14 healthy dogs. Short-chain fatty acid (SCFA; acetate, propionate, and butyrate; 1 to 100 mmol/L)-induced contractions were compared with responses obtained with acetylmethylcholine (AMCh; 10(-4) mol/L). Roles of enteric neurons, cholinergic receptors, calcium stores in the sarcoplasmic reticulum, and extracellular calcium in the SCFA-induced responses were investigated by incubating muscle strips with tetrodotoxin (1 micromol/L), atropine (1 micromol/L), ryanodine (10 micromol/L), nifedipine (1 micromol/L), ethylene glycol-bis (beta-aminoethylether)-N,N,N',N'-tetra-acetate (EGTA; 0.1 mmol/L), or an extracellular calcium-depleted (zero extracellular calcium) solution prior to the addition of propionate or butyrate. Incubation with SCFA elicited isometric stress responses (0.25 to 2.15 x 10(4) N/m2) in colonic longitudinal smooth muscle. Maximal responses to butyrate and propionate (50 mmol/L) were 37 and 23%, respectively, of the maximal AMCh response. Acetate was least effective in stimulating contractile responses. Tetrodotoxin and atropine did not affect SCFA-induced contractions. Nifedipine and zero extracellular calcium solution abolished responses to butyrate and propionate, whereas EGTA attenuated (> 60%) but did not abolish those responses. Ryanodine did not affect SCFA-induced contractile responses. The SCFA did not affect colonic circular smooth muscle. CONCLUSIONS AND CLINICAL RESPONSE: The SCFA stimulate longitudinal but not circular colonic smooth muscle contractions via a direct effect on smooth muscle. The mechanism of the SCFA effect appears to involve the influx of extracellular calcium. These findings may account for some of the effects of fiber on canine colonic motility [corrected].

Effect of inflammatory mediators on the physiology of the human Fallopian tube

The physiological basis for the use of non-steroidal anti-inflammatory drugs (NSAIDs) in the treatment of acute pelvic pain in women was examined in terms of: (i) the electrophysiological responses of epithelial cells in the human Fallopian tube; and (ii) the longitudinal and circular contractions of the myosalpinx. Epithelial cells were grown as a polarized layer in primary culture, and transepithelial potential difference (p.d.) and short-circuit current (Iscc) were recorded using a modified Ussing chamber. The inflammatory mediators histamine (0.1–100.0 µmol l-1) and platelet activating factor (PAF) (1.9–1900.0 nmol l-1) increased p.d. and Iscc in a dose-dependent manner. Pre-incubation with the NSAID diclofenac sodium (100 µmol l-1) inhibited the histamine- and PAF-induced stimulation of p.d. and Iscc. Aspirin (100 µmol l-1), ibuprofen (100 µmol l-1), indomethacin (100 µmol l-1) or naproxen (100 µmol l-1) were only partially effective. Histamine (0.1–1000.0 µmol l-1) increased the frequency of contractions of longitudinal and circular smooth muscle in segments of Fallopian tube in vitro, in a dose-dependent manner. Pre-incubation with diclofenac significantly reduced the histamine-induced stimulation of tubal smooth muscle contraction at the higher doses of histamine. The other NSAIDs had no effect. These data provide evidence that diclofenac downregulates acute inflammation in the human Fallopian tube and may be of use as an anti-inflammatory agent in the treatment of pelvic inflammatory disease.

Alterations in spontaneous contractions in vitro after repeated inflammation of rat distal colon.

In inflammatory bowel disease, smooth muscle function reportedly varies with disease duration. The aim of these studies was to determine changes in the control of spontaneous contractions in a model of experimental colitis that included reinflammation of the healed area. The amplitude and frequency of spontaneous contractions in circular smooth muscle were determined after intrarectal administration of trinitrobenzenesulfonic acid in rat distal colon. With the use of a novel paradigm, rats were studied 4 h (acute) or 28 days (healed) after the initial inflammation. At 28 days, rats were studied 4 h after a second inflammation (reinflamed) of the colon. Colitis induced transient increases in the amplitude of spontaneous contractions coincident with a loss of nitric oxide synthase activity. The frequency of contractions was controlled by constitutive nitric oxide in controls. Frequency was increased in healed and reinflamed colon and was associated with a shift in the dominance of neural constitutive nitric oxide synthase control to that of inducible nitric oxide synthase (iNOS). The initial colitis induced a remodeling of the neural control of spontaneous contractions reflecting changes in their regulation by constitutive nitric oxide synthase and iNOS.

Prostaglandin F2α(PGF2α)-induced contraction of human esophageal and lower esophageal sphincter circular smooth muscle

Prostaglandin F2α(PGF2α)-induced contraction of human esophageal and lower esophageal sphincter circular smooth muscle

Prostaglandin F2α(PGF2α)-induced contraction of human esophageal and lower esophageal sphincter circular smooth muscle

Prostaglandin F2α(PGF2α)-induced contraction of human esophageal and lower esophageal sphincter circular smooth muscle

Down-regulation of L-type calcium channels in inflamed circular smooth muscle cells of the canine colon

Background & Aims: Circular smooth muscle phasic contractions and tone are suppressed during colonic inflammation, but the contributing factors are poorly understood. This study investigated if the expression level of voltage-gated long-lasting (L-type) Ca2+ channel protein and functional Ca2+ channel current are down-regulated in the circular muscle cells of the inflamed canine colon. Methods: L-type Ca2+ channel expression was compared between normal and inflamed smooth muscle cells by Western immunoblots using an antibody directed against the pore-forming α1C-subunit, and patch-clamp methods were used to evaluate Ca2+ channel current density. Results: The expression of the L-type Ca2+ channel protein was significantly reduced in inflamed compared with normal circular smooth muscle cell membranes, and this finding was associated with suppressed levels of Ca2+ channel current in patch-clamped cells. The L-type Ca2+ channel current in normal and inflamed cells increased proportionately in response to Bay K 8644, but the maximal current density was still lower in the inflamed cells. Acetylcholine increased the L-type Ca2+ channel current in normal but not in inflamed cells. Conclusions: The expression level of L-type Ca2+ channels is down-regulated in the circular smooth muscle cell membranes of the inflamed colon, which may result in reduced Ca2+ influx. The functional and pharmacologic properties of the channels seem normal. Although some Ca2+ channels are still present in the inflamed cells, acetylcholine does not activate these channels, which may be caused by additional upstream defects in the receptor signaling cascade. The down-regulation of L-type Ca2+ channel expression may suppress circular smooth muscle contractions in the inflamed colon and contribute to the abnormalities in motility and digestion observed during inflammatory disorders.GASTROENTEROLOGY 2001;120:480-489