Nitric Oxide-mediated Relaxation by High K in Human Gastric Longitudinal Smooth Muscle

Complete resection of the gastric antrum decreased incidence and severity of delayed gastric emptying after pancreaticoduodenectomy

BACKGROUND

Delayed gastric emptying (DGE) is the main complication after pancreaticoduodenectomy (PD), but the mechanism is still unclear. The aim of this study was to elucidate the role of complete resection of the gastric antrum in decreasing incidence and severity of DGE after PD.

METHODS

Sprague-Dawley rats were divided into three groups: expanded resection (ER group), complete resection (CR group), and incomplete resection (IR group) of the gastric antrum. The tension (g) of remnant stomach contraction was observed. We analyzed the histological morphology of the gastric wall by different excisional methods after distal gastrectomy. Moreover, patients underwent PD at our department between January 2012 and May 2016 were included in the study. These cases were divided into IR group and CR group of the gastric antrum, and the clinical data were retrospectively analyzed.

RESULTS

The ex vivo remnant stomachs of CR group exhibited much greater contraction tension than others (P < 0.05). The contraction tension of the remnant stomach increased with increasing acetylcholine concentration, while remained stable at the concentration of 10 × 10^-5 mol/L. Furthermore, 174 consecutive patients were included and retrospectively analyzed in the study. The incidence of DGE was significantly lower (3.5% vs. 21.3%, P < 0.01) in CR group than in IR group. In addition, hematoxylin-eosin staining analyses of the gastric wall confirmed that the number of transected circular smooth muscle bundles were higher in IR group than in CR group (8.24 ± 0.65 vs. 3.76 ± 0.70, P < 0.05).

CONCLUSIONS

The complete resection of the gastric antrum is associated with decreased incidence and severity of DGE after PD. Gastric electrophysiological and physiopathological disorders caused by damage to gastric smooth muscles might be the mechanism underlying DGE.

Physiological function and molecular composition of ATP-sensitive K+ channels in human gastric smooth muscle

Gastric motility is controlled by slow waves. In general, the activation of the ATP-sensitive K⁺ (K_ATP) channels in the smooth muscle opposes the membrane excitability and produces relaxation. Since metabolic inhibition and/or diabetes mellitus are accompanied by dysfunctions of gastric smooth muscle, we examined the possible roles of K_ATP channels in human gastric motility. We used human gastric corpus and antrum smooth muscle preparations and recorded the mechanical activities with a conventional contractile measuring system. We also identified the subunits of the K_ATP channels using Western blot. Pinacidil (10 μM), a K_ATP channel opener, suppressed contractions to 30% (basal tone to −0.2 g) of the control. The inhibitory effect of pinacidil on contraction was reversed to 59% of the control by glibenclamide (20 μM), a K_ATP channel blocker. The relaxation by pinacidil was not affected by a pretreatment with L-arginine methyl ester, tetraethylammonium, or 4-aminopyridine. Pinacidil also inhibited the acetylcholine (ACh)-induced tonic and phasic contractions in a glibenclamide-sensitive manner (42% and 6% of the control, respectively). Other K_ATP channel openers such as diazoxide, cromakalim and nicorandil also inhibited the spontaneous and ACh-induced contractions. Calcitonin gene-related peptide (CGRP), a gastric neuropeptide, induced muscle relaxation by the activation of K_ATP channels in human gastric smooth muscle. Finally, we have found with Western blot studies, that human gastric smooth muscle expressed K_ATP channels which were composed of Kir 6.2 and SUR2B subunits.

Resveratrol and genistein inhibition of rat isolated gastrointestinal contractions and related mechanisms

AIM: To investigate the effects and underlying mechanisms of resveratrol and genistein on contractile responses of rat gastrointestinal smooth muscle.

METHODS: Isolated strips of gastrointestinal smooth muscle from Spraque-Dawley rats were suspended in organ baths containing Kreb’s solution, and the contractility of smooth muscles was measured before and after incubation with resveratrol and genistein, and the related mechanisms were studied by co-incubation with various inhibitors.

RESULTS: Resveratrol and genistein dose-dependently decreased the resting tension, and also reduced the mean contractile amplitude of gastrointestinal smooth muscle. Estrogen receptor blockades (ICI 182780 and tamoxifen) failed to alter the inhibitory effects induced by resveratrol and genistein. However, their effects were attenuated by inhibitions of α-adrenergic receptor (phentolamine), nitric oxide synthase (levorotatory-NG-nitroarginine), ATP-sensitive potassium channels (glibenclamide), and cyclic adenosine monophosphate (SQ22536). In high K⁺/Ca²⁺-free Kreb’s solution containing 0.01 mmol/L egtazic acid, resveratrol and genistein reduced the contractile responses of CaCl₂, and shifted its cumulative concentration-response curves rightward.

CONCLUSION: Resveratrol and genistein relax gastrointestinal smooth muscle viaα-adrenergic receptors, nitric oxide and cyclic adenosine monophosphate pathways, ATP-sensitive potassium channels, and inhibition of L-type Ca²⁺ channels.

H2 Receptor-Mediated Relaxation of Circular Smooth Muscle in Human Gastric Corpus: the Role of Nitric Oxide (NO)

This study was designed to examine the effects of histamine on gastric motility and its specific receptor in the circular smooth muscle of the human gastric corpus. Histamine mainly produced tonic relaxation in a concentration-dependent and reversible manner, although histamine enhanced contractility in a minor portion of tissues tested. Histamine-induced tonic relaxation was nerve-insensitive because pretreatment with nerve blockers cocktail (NBC) did not inhibit relaxation. Additionally, K⁺ channel blockers, such as tetraethylammonium (TEA), apamin (APA), and glibenclamide (Glib), had no effect. However, N^G-nitro-L-arginine methyl ester (L-NAME) and 1H-(1,2,4)oxadiazolo (4,3-A) quinoxalin-1-one (ODQ), an inhibitor of soluble guanylate cyclase (sGC), did inhibit histamine-induced tonic relaxation. In particular, histamine-induced tonic relaxation was converted to tonic contraction by pretreatment with L-NAME. Ranitidine, the H₂ receptor blocker, inhibited histamine-induced tonic relaxation. These findings suggest that histamine produced relaxation in circular smooth muscle of human gastric smooth muscle through H₂ receptor and NO/sGC pathways.

Characteristics of diprophylline-induced bidirectional modulation on rat jejunal contractility

In this study, we propose that diprophylline exerts bidirectional modulation (BM) on the isolated rat jejunal segment depending on its contractile state. The results supported the hypothesis. Diprophylline (20 µM) exerted stimulatory effects on the contractility of jejunal segment in six low contractile states while inhibitory effects in six high contractile states, showing the characteristics of BM. Diprophylline-induced stimulatory effect was significantly blocked by atropine, indicating the correlation with cholinergic activation. Diprophylline-induced inhibitory effect was partially blocked by phentolamine, propranolol, and L-N-Nitro-Arginine respectively, indicating their correlation with sympathetic activation and nitric oxide-mediated relaxing mechanisms. Diprophylline-induced BM was abolished by tetrodotoxin or in a Ca²⁺ free condition or pretreated with tyrosine kinase inhibitor imatinib, suggesting that diprophylline-induced BM is Ca²⁺ dependent, and that it requires the presence of enteric nervous system as well as pacemaker activity of interstitial cells of Cajal. Diprophylline significantly increased the reduced MLCK expression and myosin extent in constipation-prominent rats and significantly decreased the increased MLCK expression and myosin extent in diarrhea-prominent rats, suggesting that the change of MLCK expression may also be involved in diprophylline-induced BM on rat jejunal contractility. In summary, diprophylline-exerted BM depends on the contractile states of the jejunal segments, requires the presence of Ca²⁺, enteric nervous system, pacemaker activity of interstitial cells of Cajal, and MLCK-correlated myosin phosphorylation. The results suggest the potential implication of diprophylline in relieving alternative hypo/hyper intestinal motility.

Nitric oxide modulates levels of salivary Lactobacilli

OBJECTIVE

Nitric Oxide (NO) is one of the most powerful antibacterial compounds. The aim of this study was to determine the association between salivary NO, dental caries and cariogenic bacteria.

MATERIALS AND METHODS

The salivary NO concentration of 257 Korean children was analyzed by the Griess colorimetric reaction method. Salivary mutans streptococci (MS) and Lactobacilli (LB) were counted using the Dentocult MS and Dentocult LB kit, respectively. Dental caries status was examined using the WHO criteria. Confounders were age, gender, salivary flow rate and salivary buffer capacity. Analysis of covariance (ANCOVA) was used to evaluate the association among NO, salivary MS level, salivary LB level and dental caries status after adjusting for the effects of confounders.

RESULTS

A significant decrease was found in salivary NO levels as the salivary LB count increased after controlling for confounders (p = 0.049). However, the MS level, caries experience and active caries status showed no significant association.

CONCLUSION

This result indicates that NO production might be a host defense mechanism against the growth of cariogenic bacteria.

Mechanism of Relaxation Via TASK-2 Channels in Uterine Circular Muscle of Mouse

Plasma pH can be altered during pregnancy and at labor. Membrane excitability of smooth muscle including uterine muscle is suppressed by the activation of K⁺ channels. Because contractility of uterine muscle is regulated by extracellular pH and humoral factors, K⁺ conductance could be connected to factors regulating uterine contractility during pregnancy. Here, we showed that TASK-2 inhibitors such as quinidine, lidocaine, and extracellular acidosis produced contraction in uterine circular muscle of mouse. Furthermore, contractility was significantly increased in pregnant uterine circular muscle than that of non-pregnant muscle. These patterns were not changed even in the presence of tetraetylammonium (TEA) and 4-aminopyridine (4-AP). Finally, TASK-2 inhibitors induced strong myometrial contraction even in the presence of L-methionine, a known inhibitor of stretchactivated channels in myometrium. When compared to non-pregnant myometrium, pregnant myometrium showed increased immunohistochemical expression of TASK-2. Therefore, TASK-2, seems to play a key role during regulation of myometrial contractility in the pregnancy and provides new insight into preventing preterm delivery.

High k(+)-induced relaxation by nitric oxide in human gastric fundus

This study was designed to elucidate high K(+)-induced relaxation in the human gastric fundus. Circular smooth muscle from the human gastric fundus greater curvature showed stretch-dependent high K(+) (50 mM)-induced contractions. However, longitudinal smooth muscle produced stretch-dependent high K(+)-induced relaxation. We investigated several relaxation mechanisms to understand the reason for the discrepancy. Protein kinase inhibitors such as KT 5823 (1 µM) and KT 5720 (1 µM) which block protein kinases (PKG and PKA) had no effect on high K(+)-induced relaxation. K(+) channel blockers except 4-aminopyridine (4-AP), a voltage-dependent K(+) channel (K(V)) blocker, did not affect high K(+)-induced relaxation. However, N(G)-nitro-L-arginine and 1H-(1,2,4)oxadiazolo (4,3-A)quinoxalin-1-one, an inhibitors of soluble guanylate cyclase (sGC) and 4-AP inhibited relaxation and reversed relaxation to contraction. High K(+)-induced relaxation of the human gastric fundus was observed only in the longitudinal muscles from the greater curvature. These data suggest that the longitudinal muscle of the human gastric fundus greater curvature produced high K(+)-induced relaxation that was activated by the nitric oxide/sGC pathway through a K(V) channel-dependent mechanism.