The ionic basis underlying the maintenance of myogenic tone of lower esophageal sphincter circular muscle (LES) was investigated in opossum with the use of standard isometric tension and conventional intracellular microelectrode recordings in vitro. In tension recording studies, nifedipine (1 microM) reduced basal tone to 27.7 +/- 3.8% of control. The K(+) channel blockers tetraethylammonium (TEA, 2 mM), charybdotoxin (100 nM), and 4-aminopyridine (4-AP, 2 mM) enhanced resting tone, whereas apamin and glibenclamide were without affect. Cl(-) channel blockers DIDS (500 microM) and 5-nitro-2-(3-phenylpropylamino)-benzoic acid (500 microM), as well as niflumic acid (0.1-300 microM), decreased basal tone, but tamoxifen was without effect. Intracellular microelectrode recordings revealed ongoing, spontaneous, spike-like action potentials (APs). Nifedipine abolished APs and depolarized resting membrane potential (RMP). Both TEA and 4-AP significantly depolarized RMP and augmented APs, whereas niflumic acid dose-dependently hyperpolarized RMP and abolished APs. These data suggest that, in the opossum, basal tone is associated with continuous APs and that K(+) and Ca(2+)-activated Cl(-) channels have important opposing roles in the genesis of LES tone.

Objective: Intraluminal acid evokes reflex contraction of oesophageal longitudinal smooth muscle (LSM) and consequent oesophageal shortening. This reflex may play a role in the pathophysiology of oesophageal pain syndromes and hiatus hernia formation. The aim of the current study was to elucidate further the mechanisms of acid-induced oesophageal shortening. Design: Intraluminal acid perfusion of the intact opossum smooth muscle oesophagus was performed in vitro in the presence and absence of neural blockade and pharmacological antagonism of the neurokinin 2 receptor, while continuously recording changes in oesophageal axial length. In addition, the effect of these antagonists on the contractile response of LSM strips to the mast cell degranulating agent 48/80 was determined. Finally, immunohistochemistry was performed to look for evidence of LSM innervation by substance P/calcitonin gene-related peptide (CGRP)-containing axons. Results: Intraluminal acid perfusion induced longitudinal axis shortening that was completely abolished by capsaicin desensitization, substance P desensitization, or the application of the neurokinin 2 receptor antagonist MEN10376. Compound 48/80 induced sustained contraction of LSM strips in a concentrationdependent fashion and this was associated with evidence of mast cell degranulation. The 48/80-induced LSM contraction was antagonized by capsaicin desensitization, substance P desensitization and MEN10376, but not tetrodotoxin. Immunohistochemistry revealed numerous substance P/CGRP-containing neurons innervating the LSM and within the mucosa. Conclusions: This study suggests that luminal acid activates a reflex pathway involving mast cell degranulation, activation of capsaicin-sensitive afferent neurons and the release of substance P or a related neurokinin, which evokes sustained contraction of the oesophageal LSM. This pathway may be a target for treatment of oesophageal pain syndromes.

Studies on the pathophysiology of reflux esophagitis have focused on the associated motility and/or structural abnormalities, with relatively little attention directed to inflammatory mediators involved in the acid-induced mucosal injury. Mast cells line the subepithelial lamina propria in both humans and the opossum model, and are ideally positioned to respond to luminal agents that cross the mucosal barrier. To determine whether certain mast cell mediators are involved in acid-induced mucosal injury, epithelial injury scores following 60 min of luminal perfusion of the opossum esophagus with 100 mM HCl were compared in the presence and absence of two different mast cell stabilizers (disodium cromoglycate and doxantrazole) or the selective platelet-activating factor antagonist TCV-309. In control animals acid perfusion caused release of PAF and significant epithelial injury, characterized by epithelial sloughing and cleft formation. This injury was unaffected by pretreatment with disodium cromoglycate or doxantrazole but was completely prevented by TCV-309 (histology damage score, 2.40+/-0.28 in controls vs 0.50 +/- 0.14 in TCV-309-treated animals). These studies suggest that platelet-activating factor is an important mediator of acid-induced esophageal mucosal damage.

This paper presents a novel approach that demonstrates the usefulness of electrorheological fibril formation to form f-3 connected ceramic-polymer composites. These fillers include ferroelectric, polar, metal, semiconductor, and superconductor crystallite powders. Patterned distributions of ceramic fillers within the polymer matrix can be induced by electric fields applied between patterned electrodes.

Background and purpose:The ionic mechanisms underlying nitrergic inhibitory junction potentials (IJPs) in gut smooth muscle remain a matter of debate. Recently, it has been reported that opening of TWIK-related K + channel 1 (TREK-1) K + channels contributes to the nitrergic IJP in colonic smooth muscle. We investigated the effects of TREK-1 channel blockers on nitrergic neurotransmission in mouse and opossum lower oesophageal sphincter (LOS) circular smooth muscle (CSM). Experimental approach:The effects of TREK-1 channel blockers were characterized pharmacologically in murine and opossum gut smooth muscle using conventional intracellular and tension recordings. Key results: In LOS, L-methionine depolarized the resting membrane potential (RMP) but did not inhibit the nitrergic IJP. Cumulative application of theophylline hyperpolarized the RMP and inhibited the nitrergic IJP concentration dependently. The induced membrane hyperpolarization was prevented by pre-application of caffeine, but not by 1H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one. 8-Br-cAMP significantly hyperpolarized membrane potential and increased the amplitude of the nitrergic IJP. In opossum LOS muscle strips, L-methionine increased resting tone but had no effect on nerve-mediated LOS relaxation. On the other hand, theophylline markedly inhibited tone. In CSM from mouse proximal colon, L-methionine caused modest inhibition of nitrergic IJPs. Conclusions and implications:TREK-1 channels were not involved in the nitrergic IJP in LOS CSM. Not only does L-methionine have no effect on the nitrergic IJP or LOS relaxation, but the effect of theophylline appears to be due to interruption of Ca 2+ -releasing pathways (i.e. caffeine-like effect) rather than via blockade of TREK-1 channels.