NO/cyclic GMP pathway mediates the relaxation of feline lower oesophageal sphincter

Effects of chronic ethanol consumption on rat upper gastrointestinal system: functional and histologic findings

The purpose of the present study was to determine the effect of chronic alcohol consumption on reactivity of esophageal tunica muscularis mucosae (TMM) and lower esophageal sphincter (LES) smooth muscle. Six male rats in alcohol-fed group received ethanol (7.2% v/v) in a modified liquid diet for 4 weeks. Two control groups were used; six rats in the standard diet-fed group received rat chow and water for 4 weeks. Six rats in sucrose-fed group were given sucrose and received a liquid diet. The smooth muscle reactivity of TMM and LES strips from ethanol-fed and control animals was evaluated in organ chambers. Also histologic study was undertaken to show effects of chronic alcohol consumption. Maximum contractile responses of TMM to KCl and carbachol were decreased in the ethanol-fed group compared to the control groups. Relaxant responses to serotonin were decreased in the ethanol-fed group compared to the control groups. In TMM, isoproterenol- and papaverine-induced relaxant responses were similar in the ethanol-fed and control groups. In LES smooth muscle, relaxant responses to papaverine or isoproterenol were similar in the control groups and the ethanol-fed group. There was no change in agonist potency among the groups. The relaxation response elicited by nicotine and sodium nitroprusside (SNP) or contractile response elicited by carbachol and 80 mM KCl was decreased with maximum responses and pD(2) values, in the ethanol-fed group compared to that of the control groups in LES. Decreased nNOS immunoreactivity in myenteric plexus was found in alcohol-exposed group compared to control groups. Our findings suggest that chronic alcohol consumption impairs relaxant and contractile responses of both TMM and LES smooth muscle and it may contribute to gastroesophageal reflux commonly seen after alcohol binges.

Pharmacologic specificity of nicotinic receptor-mediated relaxation of muscarinic receptor precontracted human gastric clasp and sling muscle fibers within the gastroesophageal junction

Relaxation of gastric clasp and sling muscle fibers is involved the transient lower esophageal sphincter relaxations underlying the pathophysiology of gastroesophageal reflux disease (GERD). These fibers do not contribute tone to the high-pressure zone in GERD patients, indicating their role in pathophysiology. This study identifies some mediators of the nicotine-induced relaxation of muscarinic receptor precontracted gastric clasp and sling fibers. Muscle strips from organ donors precontracted with bethanechol were relaxed with nicotine and then rechallenged after washing and adding inhibitors tetrodotoxin (TTX), the nitric-oxide synthase inhibitor L-nitro-arginine methyl ester (L-NAME), the β-adrenoceptor antagonist propranolol, the glycine receptor antagonist strychnine or ginkgolide B, and the GABA(A) receptor antagonist bicuculline or 2-(3-carboxypropyl)-3-amino-6-(4 methoxyphenyl)pyridazinium bromide [(gabazine) SR95531]. TTX only inhibited clasp fiber relaxations. L-NAME and propranolol inhibited, and ginkgolide B was ineffective in both. SR95531 was ineffective in clasp fibers and partially effective in sling fibers. Strychnine and bicuculline prevented relaxations with low potency, indicating actions not on glycine or GABA(A) receptors but more consistent with nicotinic receptor blockade. Bethanechol-precontracted fibers were relaxed by the nitric oxide donor S-nitroso-N-acetyl-DL-penicillamine and by the β-adrenergic agonist isoproterenol (clasp fibers only) but not by the glycine receptor agonist taurine or glycine or the GABA(A) agonist muscimol. These data indicate that nicotinic receptor activation mediates relaxation via release of nitric oxide in clasp and sling fibers, norepinephrine acting on β-adrenoceptors in clasp fibers, and GABA acting on GABA(A) receptors in sling fibers. Agents that selectively prevent these relaxations may be useful in the treatment of GERD.

Nitric oxide activation of a potassium channel (BKCa) in feline lower esophageal sphincter

AIM: To assess the effect of nitric oxide (NO) on the large conductance potassium channel (BK_Ca) in isolated circular (CM) and sling (SM) muscle cells and muscle strips from the cat lower esophageal sphincter (LES) to determine its regulation of resting tone and relaxation.

METHODS: Freshly enzymatically-digested and isolated circular smooth muscle cells were prepared from each LES region. To study outward K⁺ currents, the perforated patch clamp technique was employed. To assess LES resting tone and relaxation, muscle strips were mounted in perfused organ baths.

RESULTS: (1) Electrophysiological recordings from isolated cells: (a) CM was more depolarized than SM (-39.7 ± 0.8mV vs -48.1 ± 1.6 mV, P < 0.001), and maximal outward current was similar (27.1 ± 1.5 pA/pF vs 25.7 ± 2.0 pA/pF, P > 0.05); (b) The NO donor sodium nitroprusside (SNP) increased outward currents only in CM (25.9 ± 1.9 to 46.7 ± 4.2 pA/pF, P < 0.001) but not SM (23.2 ± 3.1 to 27.0 ± 3.4 pA/pF, P > 0.05); (c) SNP added in the presence of the BK_Ca antagonist iberiotoxin (IbTX) produced no increase in the outward current in CM (17.0 ± 2.8 vs 13.7 ± 2.2, P > 0.05); and (d) L-NNA caused a small insignificant inhibition of outward K⁺ currents in both muscles; and (2) Muscle strip studies: (a) Blockade of the nerves with tetrodotoxin (TTX), or BK_Ca with IbTX had no significant effect on resting tone of either muscle; and (b) SNP reduced tone in both muscles, and was unaffected by the presence of TTX or IbTX.

CONCLUSION: Exogenous NO activates BK_Ca only in CM of the cat. However, as opposed to other species, exogenous NO-induced relaxation is predominantly by a non-BK_Ca mechanism, and endogenous NO has minimal effect on resting tone.

Effect of hydrogen peroxide on VIP-induced relaxation of the cat lower esophageal sphincter

We investigated the effects of hydrogen peroxide (H2O2) on relaxation of the cat lower esophageal sphincter (LES). Vasoactive intestinal peptide (VIP) caused dose-dependent relaxation of LES, and H2O2 reduced VIP-induced relaxation. Relaxation was also attenuated by pertussis toxin (PTX), indicating a Gi/o component. VIP treatment increased [35S]GTPgammaS binding to Gs and Gi3 protein, but not to Go, Gq, Gil or Gi2. This increase in Gs or Gi3 binding was reduced by H2O2. However, the relaxation induced by sodium nitroprusside (SNP), 3-morpholino sydnomine (SIN-1), 8-br cGMP (cGMP analog), forskolin (adenylate cyclase activator), and dibutyryl-cAMP (a stable cAMP analog) was not reduced by H2O2. These data suggest that H202 inhibits VIP-induced relaxation via a Gi-dependent pathway, perhaps by inhibiting the activation of G(i3) or Gs downstream of the VIP receptor and independent of cAMP or NO-cGMP signaling.

Regulation of basal tone, relaxation and contraction of the lower oesophageal sphincter. Relevance to drug discovery for oesophageal disorders

The lower oesophageal sphincter (LOS) is a specialized region of the oesophageal circular smooth muscle that allows the passage of a swallowed bolus to the stomach and prevents the reflux of gastric contents into the oesophagus. The anatomical arrangement of the LOS includes semicircular clasp fibres adjacent to the lesser gastric curvature and sling fibres following the greater gastric curvature. Such anatomical arrangement together with an asymmetric intrinsic innervation and distinct proportion of neurotransmitters in both regions produces an asymmetric pressure profile. The LOS tone is myogenic in origin and depends on smooth muscle properties that lead to opening of L-type Ca(2+) channels; however it can be modulated by enteric motor neurons, the parasympathetic and sympathetic extrinsic nervous system and several neurohumoral substances. Nitric oxide synthesized by neuronal NOS is the main inhibitory neurotransmitter involved in LOS relaxation. Different putative neurotransmitters have been proposed to play a role together with NO. So far, only ATP or related purines have shown to be co-transmitters with NO. Acetylcholine and tachykinins are involved in the LOS contraction acting through acetylcholine M(3) and tachykinin NK(2) receptors. Nitric oxide can also be involved in the regulation of LOS contraction. The understanding of the mechanisms that originate and modulate LOS tone, relaxation and contraction and the characterization of neurotransmitters and receptors involved in LOS function are important to develop new pharmacological tools to treat primary oesophageal motor disorders and gastro-oesophageal reflux disease.

The structural characteristics and expression of neuropeptides in the esophagus of patients with congenital esophageal atresia and tracheoesophageal fistula

PURPOSE

The aim of this study was to investigate the structural characteristics and the expression of a group of neuropeptides in the esophagus of patients with congenital esophageal atresia and tracheoesophageal fistula (EA-TEF), as well to elucidate the roles of these neuropeptides in the pathogenesis of postoperative incoordination of esophagus after successful surgical repair of EA-TEF.

METHODS

Twenty-four specimens from distal tracheoesophageal fistulas of patients with EA-TEF (EA-TEF group) and 10 esophageal specimens from neonates who died of nonesophageal diseases (control group) were studied. All of the specimens were subjected to routine pathologic study, ultrastructural observation, and immunohistochemical staining for neuron-specific enolase, substance P, vasoactive intestinal polypeptide, and nitric oxide synthase.

RESULTS

In the EA-TEF group, mitochondria were distributed along the membrane of smooth muscle cell, whereas mitochondria in the control group were distributed along the karyotheca of the smooth muscle cells. The ratio of granulated vesicles to clear vesicles in the varicosity of the intramuscular motor nerve ending of the EA-TEF group (0.520 +/- 0.137) was much higher than that in the control group (0.192 +/- 0.020, P < .05). The percentages of specimens shown to have positive expression of neuron-specific enolase and substance P in the EA-TEF group (20.8% and 12.5%, respectively) were significantly lower than those in the control group (90% and 80% respectively, P < .05). The percentages of specimens shown to have positive expression of vasoactive intestinal polypeptide and nitric oxide synthase in the EA-TEF group (83.3% and 75%, respectively) were significantly higher than that in the control group (30% and 10% respectively, P < .05).

CONCLUSION

Imbalance of neurotransmitters excretion in nerve vesicle, abnormal intrinsic dysplasia of nerve plexus and increased expression of certain neuropeptides were the main characteristics of esophagus with abnormal intrinsic innervation, which may be responsible for the postoperative esophageal dysfunction of EA-TEF.

Effects of endogenous and exogenous nitric oxide on electrical responses of circular smooth muscle isolated from the guinea-pig stomach antrum

The effects of endogenous and exogenous nitric oxide (NO) on electrical activity were investigated in circular smooth muscle preparations isolated from the guinea-pig stomach antrum. The actions of endogenous NO were evaluated from the effects of inhibition of NO synthesis by N(omega)-nitro-L-arginine (nitroarginine), while those of exogenous NO were assessed from the effects of SIN-1, an NO donor. Antral circular smooth muscle generated slow potentials periodically at a frequency of about 1 cycle per min (cpm), and unitary potentials were also generated in a random fashion in the interval between slow potentials. Application of nitroarginine (10(-5) M) increased the frequency of slow potentials, with no significant alteration of the resting membrane potential and amplitude of slow potentials. Frequency analysis of unitary potentials revealed that nitroarginine also increased the spectral density at 0.01-1 Hz frequency. The refractory period for the generation of slow potentials evoked by depolarizing pulses was about 10 s, but was decreased to 6 s by nitroarginine. In the presence of nitroarginine, SIN-1 (10(-9)-10(-7) M) reduced the amplitude and frequency of slow potentials: low concentrations (<10(-8) M) reduced only the frequency of slow potentials, while higher concentrations (10(-8)-10(-7) M) reduced both the amplitude and frequency of slow potentials, in a concentration-dependent manner, before abolishing the slow potentials. The power spectrum of the unitary potentials indicated that SIN-1 (>10(-8) M) reduced the spectral density at 0.01-1 Hz frequency. The refractory period for the generation of slow potentials was increased again to about 10 s by SIN-1. Thus, the excitatory effects of nitroarginine could be antagonized by SIN-1, suggesting that the inhibitory effects of endogenous NO are comparable to those of exogenous NO produced by SIN-1. The results also suggested that the effects of NO on smooth muscle are insignificant and NO selectively inhibits the activity of intramuscular interstitial cells of Cajal (ICC-IM).