Background: Multichannel electrogastrography (M-EGG) can be used to evaluate gastrointestinal motility. The myoelectric activity of the remnant stomach after surgery has not been measured by M-EGG. This study examined whether myoelectric activity varied with surgical technique and compared vagus nerve-preserving distal gastrectomy (VP-DG) with standard distal gastrectomy without vagus nerve preservation (DG). Furthermore, we examined the relationship between the M-EGG findings and patients’ postoperative symptoms. Methods: Twenty-six patients who underwent VP-DG, 20 who underwent DG, and 12 healthy volunteers as controls were examined with M-EGG. The Gastrointestinal Symptom Rating Scale (GSRS) was used to assess postoperative symptoms. Results: Longer periods of normal gastric function (normogastria, 2.0–4.0 cycle min–1) were detected in channel 1 in the VP-DG group than in the DG group in either the fasted or fed state (P<0.05). The percentage of slow wave coupling (%SWC) in the fed state correlated negatively with GSRS scores (reflux, r=–0.59, P=0.02; abdominal pain, r=–0.51, P=0.04, indigestion, r=–0.59, P=0.02 and total score, r=–0.75, P=0.02). Conclusions: Slow waves can be recorded non-invasively using M-EGG in the remnant stomach following gastrectomy. The VP-DG group showed better preserved gastric myoelectric activity than the DG group, and the %SWC showed a significant negative correlation with scores of GSRS (reflux, abdominal pain, indigestion and total score) in the VP-DG group.
Ent-7α-hydroxytrachyloban-18-oic acid, a trachylobane diterpene from Xylopia langsdorfiana, has previously been shown to relax the guinea-pig trachea in a concentration-dependent manner. In this study we aimed to elucidate the mechanisms underlying this action and so contribute to the discovery of natural products with therapeutic potential. A possible interaction between diterpene and the Ca2+-calmodulin complex was eliminated as chlorpromazine (10-6 M), a calmodulin inhibitor, did not significantly alter the diterpene-induced relaxation (pD2 = 4.38 ± 0.07 and 4.25 ± 0.07; mean ± S.E.M., n=5). Trachylobane-318 showed a higher relaxant potency when the trachea was contracted by 18 mM KCl than it did with 60 mM KCl (pD2 = 4.90 ± 0.25 and 3.88 ± 0.01, n=5), suggesting the possible activation of K+ channels. This was confirmed, as in the presence of 10 mM TEA+ (a non-selective K+ channel blocker), diterpene relaxation potency was significantly reduced (pD2 = 4.38 ± 0.07 to 4.01 ± 0.06, n=5). Furthermore, K+ channel subtypes KATP, KV, SKCa and BKCa seem to be modulated positively by trachylobane-318 (pD2 = 3.91 ± 0.003, 4.00 ± 0.06, 3.45 ± 0.14 and 3.80 ± 0.05, n=5) but not the Kir subtype channel (pD2 = 4.15 ± 0.10, n=5). Cyclic nucleotides were not involved as the relaxation due to aminophylline (pD2 = 4.27 ± 0.09, n=5) was not altered in the presence of 3 × 10-5 M trachylobane-318 (pD2 = 4.46 ± 0.08, n=5). Thus, at a functional level, trachylobane-318 seems to relax the guinea-pig trachea by positive modulation of K+ channels, particularly the KATP, KV, SKCa and BKCa subtypes.
Rho-associated kinase (ROK) activation plays an important role in K+-induced contraction of rat caudal arterial smooth muscle (Mita et al., Biochem J. 2002; 364: 431–40). The present study investigated a potential role for tyrosine kinase activity in K+-induced RhoA activation and contraction. The non-selective tyrosine kinase inhibitor genistein, but not the src family tyrosine kinase inhibitor PP2, inhibited K+-induced sustained contraction (IC50 = 11.3 ± 2.4 μM). Genistein (10 μM) inhibited the K+-induced increase in myosin light chain (LC20) phosphorylation without affecting the Ca2+ transient. The tyrosine phosphatase inhibitor vanadate induced contraction that was reversed by genistein (IC50 = 6.5 ± 2.3 μM) and the ROK inhibitor Y-27632 (IC50 = 0.27 ± 0.04 μM). Vanadate also increased LC20 phosphorylation in a genistein- and Y-27632-dependent manner. K+ stimulation induced translocation of RhoA to the membrane, which was inhibited by genistein. Phosphorylation of MYPT1 (myosin-targeting subunit of myosin light chain phosphatase) was significantly increased at Thr855 and Thr697 by K+ stimulation in a genistein- and Y-27632-sensitive manner. Finally, K+ stimulation induced genistein-sensitive tyrosine phosphorylation of proteins of ~55, 70 and 113 kDa. We conclude that a genistein-sensitive tyrosine kinase, activated by the membrane depolarization-induced increase in [Ca2+]i, is involved in the RhoA/ROK activation and sustained contraction induced by K+.
Chronic obstructive pulmonary disease (COPD) is among the leading causes of morbidity and mortality worldwide. Glucocorticoids are currently the most applicable anti-inflammatory treatment for COPD. However, a subset of COPD subjects is relatively insensitive to this treatment. Fenspiride, a non-corticosteroid anti-inflammatory drug, has been described to have beneficial effects in patients with COPD, although the mechanism of its action is not well known. The effect of fenspiride on contractile activity of bronchial smooth muscle was studied in a rat model of COPD induced by long-term exposure of the animals to nitrogen dioxide (NO2). Contractile activity of bronchial smooth muscle was evaluated in vitro. Isometric contraction of bronchial preparations was measured following electrical stimulation. Fenspiride administration to rats during the acute stage of COPD (15 days of NO2 exposure) prevented the bronchial constriction induced by NO2. The bronchodilator effect of a low-dose of fenspiride (0.15 mg/kg) was mediated by interaction with the nerve endings of capsaicin-sensitive C-fibers. Interaction of fenspiride with C-fibers was shown to prevent initiation of neurogenic inflammation, as evidenced by lack of COPD-like structural changes in the lungs. The bronchodilator effect of a high-dose of fenspiride (15 mg/kg) was mediated not only by the afferent component, but also involved a direct relaxing effect on smooth muscle cells. The anti-inflammatory and bronchodilator effects of a low-dose of fenspiride may be used for prevention of COPD development in individuals from high-risk cohorts exposed to aggressive environmental factors.
Various studies have shown that pregnancy is associated with gastrointestinal complaints that might result from disturbance of the normal contractile pattern of smooth muscle. Progesterone is an important steroid hormone, which plays a crucial role in female pregnancy. Progesterone affects muscle cells by genomic mechanisms, through nuclear receptors, and non-genomic mechanisms, through unidentified pathways. Non-genomic actions were defined as those occurring within 10 min of progesterone exposure. The aim of the present study was to investigate the non-genomic effect of progesterone on Rho kinase II activity in gastric smooth muscle. Single smooth muscle cells of the stomach obtained from Sprague Dawley rats were used. Dispersed gastric smooth muscle cells were treated with progesterone or acetylcholine (ACh) separately. Cells designated for progesterone treatment were incubated with 1 μM progesterone for 10 min. Rho kinase II expression and both basal and ACh-induced Rho kinase II activity were measured via specifically designed enzyme-linked immunosorbent assay (ELISA) and activity assay kits respectively in both control and progesterone-treated groups. Progesterone inhibited the ACh-induced, but not the basal, Rho kinase II activity in dispersed gastric smooth muscle cells without affecting its expression level. This study suggested that progesterone can rapidly affect the contractile activity of isolated gastric smooth muscle cells in rats via inhibition of the Rho kinase II pathway.
Inhibitory effects of docosahexaenoic acid (DHA) on blood vessel contractions induced by various constrictor stimulants were investigated in the rat thoracic aorta. The inhibitory effects of DHA were also compared with those of eicosapentaenoic acid (EPA) and linoleic acid (LA). DHA exhibited a strong inhibitory effect on the sustained contractions induced by U46619, a TXA2 mimetic. This inhibitory effect of DHA was not affected by removal of the endothelium or by treatment with either indomethacin or Nω-nitro-l-arginine. DHA also significantly diminished PGF2α-induced contraction but did not show any appreciable inhibitory effects on the contractions to both phenylephrine (PE) and high-KCl. Similarly, EPA exhibited significant inhibitory effects against the contractions induced by both U46619 and PGF2α without substantially affecting either PE- or high-KCl-induced contractions. However, both DHA and EPA generated more potent inhibitions against contractions induced by U46619 than those by PGF2α. In contrast, LA did not show significant inhibitory effects against any contractions, including those induced by U46619. The present findings suggest that DHA and EPA elicit more selective inhibition against blood vessel contractions that are mediated through stimulation of prostanoid receptors than those through α-adrenoceptor stimulation or membrane depolarization. Although DHA and EPA have similar inhibitory potencies against prostanoid receptor-mediated contractions, they had a more potent inhibition against TXA2 receptor (TP receptor)-mediated contractions than against PGF2α receptor (FP receptor)-mediated responses. Selective inhibition by either DHA or EPA of prostanoid receptor-mediated blood vessel contractions may partly underlie the mechanisms by which these ω-3 polyunsaturated fatty acids exert their circulatory-protective effects.
Electrogastrography (EGG) is a non-invasive diagnostic motility for recording gastric myoelectrical activity. Gastric myoelectrical activity was first recorded in 1922. Advances in recording equipment enabled widespread use of cutaneous EGG after 1985. Later, introduction of multichannel EGG (M-EGG) enabled measurement of electrical activity transmission. At present, M-EGG findings are used as objective indicators of gastric motility disorders caused by various diseases. EGG measures two categories of gastric electrical activity: electrical response activity, or spike potentials; and electrical control activity, or slow waves. The appearance of abnormal rhythmic electrical activity is indicative of abnormalities in gastric motility. The normal frequency range of gastric electrical activity (normogastria) is around 3 cycles per?min. Multiple EGG parameters assist in the assessment of gastric myoelectrical activity, and significant correlations between EGG and other gastric motility tests have been demonstrated in many studies. In Japan, however, EGG remains in the exploratory stage, and its clinical use is limited. There are large variations in procedures and systems used in previous studies, thus there is a need for standardization of EGG procedures and technical terminology. Here, we outline the current status of EGG and report the M-EGG procedures used in our department in addition to our M-EGG findings.
Blebbistatin, a potent inhibitor of myosin II, has inhibiting effects on Ca2+-induced contraction and contractile filament organization without affecting the Ca2+-sensitivity to the force and phosphorylation level of myosin regulatory light chain (MLC20) in skinned (cell membrane permeabilized) taenia cecum from the guinea pig (Watanabe et al., Am J Physiol Cell Physiol. 2010; 298: C1118–26). In the present study, we investigated blebbistatin effects on the contractile force of skinned tracheal muscle, in which myosin filaments organization is more labile than that in the taenia cecum. Blebbistatin at 10 μM or higher suppressed Ca2+-induced tension development at any given Ca2+ concentration, but had little effects on the Ca2+- induced myosin light chain phosphorylation. Also blebbistatin at 10 μM and higher significantly suppressed GTP-γS-induced “sensitized” force development. Since the force inhibiting effects of blebbistatin on the skinned trachea were much stronger than those in skinned taenia cecum, blebbistatin might directly affect myosin filaments organization.
Migrating motor complex (MMC) is well characterized by the appearance of gastrointestinal (GI) contractions in the interdigestive state. The physiological importance of gastric MMC is a mechanical and chemical cleansing of the empty stomach in preparation for the next meal. MMC cycle is mediated via the interaction between motilin and 5-hydroxytryptamine (5-HT) by the positive feedback mechanism in conscious dogs. Luminal administration of 5-HT initiates duodenal phase II and phase III with a concomitant increase of plasma motilin release. Duodenal 5-HT concentration is increased during gastric phase II and phase III. Intravenous infusion of motilin increases luminal 5-HT content and induces phase III. 5-HT4 antagonists significantly inhibit both of gastric and intestinal phase III, while 5-HT3 antagonists inhibit only gastric phase III. These suggest that gastric MMC is regulated via vagus, 5-HT3/4 receptors and motilin, while intestinal MMC is regulated via intrinsic primary afferent neurons (IPAN) and 5-HT4 receptors. We propose the possibility that maximally released motilin by a positive feedback depletes 5-HT granules in the duodenal EC cells, resulting in no more contractions. Stress is highly associated with the pathogenesis of functional dyspepsia (FD). Acoustic stress attenuates gastric phase III without affecting intestinal phase III in conscious dogs, via reduced vagal activity. Subset of FD patients shows reduced vagal activity and impaired gastric phase III. The impaired gastric MMC may aggravate dyspeptic symptoms following a food ingestion. Maintaining MMC cycle in the interdigestive state is an important factor to prevent the postprandial dyspeptic symptoms.
Enhanced airway smooth muscle (ASM) contraction is an important component in the pathophysiology of asthma. We have shown that ligand gated chloride channels modulate ASM contractile tone during the maintenance phase of an induced contraction, however the role of chloride flux in depolarization-induced contraction remains incompletely understood. To better understand the role of chloride flux under these conditions, muscle force (human ASM, guinea pig ASM), peripheral small airway luminal area (rat ASM) and airway smooth muscle plasma membrane electrical potentials (human cultured ASM) were measured. We found ex vivo guinea pig airway rings, human ASM strips and small peripheral airways in rat lungs slices relaxed in response to niflumic acid following depolarization-induced contraction induced by K+ channel blockade with tetraethylammonium chloride (TEA). In isolated human airway smooth muscle cells TEA induce depolarization as measured by a fluorescent indicator or whole cell patch clamp and this depolarization was reversed by niflumic acid. These findings demonstrate that ASM depolarization induced contraction is dependent on chloride channel activity. Targeting of chloride channels may be a novel approach to relax hypercontractile airway smooth muscle in bronchoconstrictive disorders.