Diffuse Esophageal Narrowing in Eosinophilic Esophagitis: A Barium Contrast Study.

BACKGROUND: Patients with eosinophilic esophagitis (EoE) present with mechanical type dysphagia. Barium esophagrams occasionally demonstrate focal strictures or multiple concentric rings. Diffuse narrowing has also been reported but may be difficult to recognize because of lack of normative data. AIM: The aim of this study is to assess esophageal diameters at multiple sites in healthy controls in comparison with EoE patients. METHODS: A standardized barium swallow was performed in 22 healthy male volunteers without esophageal symptoms and compared with 10 untreated EoE patients. A radiopaque ruler attached at the subject's back was used to measure maximal esophageal diameter at three esophageal sites by a blinded observer. Peak intraepithelial eosinophil counts and Mayo Dysphagia Questionnaire scores were correlated to esophageal diameters in EoE patients. RESULTS: Two of 10 EoE patients had areas of focal narrowing on barium Xray. Esophageal diameters were significantly less at all three esophageal sites in EoE patients compared with controls. Using a total esophageal diameter score (i.e., sum of the three diameters) to establish the 95th percentile for minimal diameter in controls, four of 10 EoE patients fell below the normal range. There was no significant correlation between esophageal diameters, peak eosinophil counts and any of the Mayo Dysphagia Questionnaire severity scores. CONCLUSION: Patients with EoE have a diffusely narrow esophagus in comparison to healthy controls, and this abnormality may not be appreciated without using appropriate normative data.

Sustained esophageal longitudinal smooth muscle contraction may not be a cause of noncardiac chest pain.

BACKGROUND: The etiology of noncardiac chest pain (NCCP) is poorly understood. Some evidence suggests that it may be related to sustained esophageal contractions (SECs) of longitudinal smooth muscle. This study attempts to evaluate whether SECs play a role in symptom production in NCCP patients. METHODS: This was a prospective double-blind study comparing NCCP patients to healthy controls. Subjects underwent high-resolution esophageal manometry followed by infusions of normal saline and 0.1N hydrochloric acid into the esophagus. Pain intensity was recorded during each minute of the infusion using a visual analog scale between 0 and 10. Two blinded investigators measured the esophageal length at the end of the saline and acid infusion periods as well as the point at which esophageal shortening began using the computer based manometry software. KEY RESULTS: Seventeen NCCP patients and 16 controls completed the study. 64% of study subjects demonstrated esophageal shortening in response to acid infusion with mean shortening of 0.4 ± 0.54 cm. The mean decrease in esophageal length with acid was similar between the groups (1.9% ± 2.6% for NCCP patients vs 1.7% ± 2.4% for controls, P = .82). There was no correlation between pain onset and esophageal shortening. CONCLUSIONS AND INFERENCES: NCCP patients did not appear to have an exaggerated esophageal shortening response to intraluminal acid. As well, there was poor temporal correlation between esophageal shortening and symptoms. Thus, acid-induced SECs may not play a significant role in pain production in NCCP patients.

Stress increases descending inhibition in mouse and human colon.

BACKGROUND: A relationship between stress and the symptoms of irritable bowel syndrome (IBS) has been well established but the cellular mechanisms are poorly understood. Therefore, we investigated effects of stress and stress hormones on colonic descending inhibition and transit in mouse models and human tissues. METHODS: Stress was applied using water avoidance stress (WAS) in the animal model or mimicked using stress hormones, adrenaline (5 nM), and corticosterone (1 µM). Intracellular recordings were obtained from colonic circular smooth muscle cells in isolated smooth muscle/myenteric plexus preparations and the inhibitory junction potential (IJP) was elicited by nerve stimulation or balloon distension oral to the site of recording. KEY RESULTS: Water avoidance stress increased the number of fecal pellets compared to control (p < 0.05). WAS also caused a significant increase in IJP amplitude following balloon distension. Stress hormones also increased the IJP amplitude following nerve stimulation and balloon distension (p < 0.05) in control mice but had no effect in colons from stressed mice. No differences were observed with application of ATP between stress and control tissues, suggesting the actions of stress hormones were presynaptic. Stress hormones had a large effect in the nerve stimulated IJP in human colon (increased >50%). Immunohistochemical studies identified alpha and beta adrenergic receptor immunoreactivity on myenteric neurons in human colon. CONCLUSIONS & INFERENCES: These studies suggest that WAS and stress hormones can signal via myenteric neurons to increase inhibitory neuromuscular transmission. This could lead to greater descending relaxation, decreased transit time, and subsequent diarrhea.

Opportunity costs of gastrointestinal endoscopic training in Canada.

BACKGROUND: No data exist to define the opportunity costs related to instruction in endoscopic procedures in Royal College of Physicians and Surgeons of Canada-accredited teaching centres. Academic and institutional administrators expect staff to achieve acceptable performance standards. There is a need to measure some of the effects of training activity in the establishment of such standards. OBJECTIVE: To measure the effect of resident training in colonoscopy on real procedure times and, as a secondary goal, to estimate procedural losses related to the process of training. METHODS: Real procedure times for ambulatory colonoscopy in a single academic, hospital-based endoscopy unit were documented. Times for certified endoscopy instructors functioning solo were compared with times for procedures involving trainees at several levels of colonoscopic experience. Procedural reductions associated with resident training were estimated based on the parameters derived from the results. The analysis was executed retrospectively using prospectively collected data. RESULTS: Resident training prolonged procedure times for ambulatory colonoscopy by 50%. The trainee effect was consistent, although variable in degree, among a variety of endoscopy instructors. Such increased procedure times have the potential to reduce case throughput and endoscopist remuneration. CONCLUSIONS: Resident training in colonoscopy in a Canadian certified training program has significant negative effects on case throughput and endoscopist billings. These factors should be considered in any assessment of performance in similar training environments.

Wait times for gastroenterology consultation in Canada: the patients' perspective.

Long wait times for health care have become a significant issue in Canada. As part of the Canadian Association of Gastroenterology's Human Resource initiative, a questionnaire was developed to survey patients regarding wait times for initial gastroenterology consultation and its impact. A total of 916 patients in six cities from across Canada completed the questionnaire at the time of initial consultation. Self-reported wait times varied widely, with 26.8% of respondents reporting waiting less than two weeks, 52.4% less than one month, 77.1% less than three months, 12.5% reported waiting longer than six months and 3.6% longer than one year. One-third of patients believed their wait time was too long, with 9% rating their wait time as 'far too long'; 96.4% believed that maximal wait time should be less than three months, 78.9% believed it should be less than one month and 40.3% believed it should be less than two weeks. Of those working or attending school, 22.6% reported missing at least one day of work or school because of their symptoms in the month before their appointment, and 9.0% reported missing five or more days in the preceding month. A total of 20.2% of respondents reported being very worried about having a serious disease (ie, scored 6 or higher on 7-point Likert scale), and 17.6% and 14.8%, respectively, reported that their symptoms caused major impairment of social functioning and with the activities of daily living. These data suggest that a significant proportion of Canadians with digestive problems are not satisfied with their wait time for gastroenterology consultation. Furthermore, while awaiting consultation, many patients experience an impaired quality of life because of their gastrointestinal symptoms.

Proteinase-activated receptor-2 activation evokes oesophageal longitudinal smooth muscle contraction via a capsaicin-sensitive and neurokinin-2 receptor-dependent pathway.

BACKGROUND: Intraluminal acid evokes sustained oesophageal longitudinal smooth muscle (LSM) contraction and oesophageal shortening, which may play a role in oesophageal pain and the aetiology of hiatus hernia. In the opossum model, this reflex has been shown to involve mast cell activation and release of neurokinins from capsaicin-sensitive neurons. The aim of this study was to determine whether proteinase-activated receptor-2 (PAR-2) activation evokes reflex LSM contraction via similar mechanisms. METHODS: Tension recording studies were performed using opossum oesophageal LSM strips in the presence and absence of pharmacological agents. In addition, the effect of trypsin on single isolated LSM cells was determined using videomicroscopy, and the expression of PAR-2 in oesophageal tissue was examined using immunohistochemistry. KEY RESULTS: The PAR-2 agonist trypsin evoked sustained, concentration-dependent contraction of LSM muscle strips, but had no effect on isolated LSM cells. The trypsin-induced contraction was blocked by capsaicin desensitization, substance P (SP) desensitization or application of the selective neurokinin-2 (NK-2) receptor antagonist MEN 10376. Immunohistochemistry revealed co-localization of SP, calcitonin gene-related peptide and PAR-2 in axons of opossum oesophageal LSM. CONCLUSIONS & INFERENCES: Longitudinal smooth muscle contraction induced by trypsin involves capsaicin-sensitive neurons and subsequent activation of NK-2, which is identical to the pathway involved in acid-induced LSM contraction and oesophageal shortening. This suggests that acid-induced LSM contraction may involve mast cell-derived mediators that activate capsaicin-sensitive neurons via PAR-2.

Neurotransmission in lower esophageal sphincter of W/Wv mutant mice.

To address the controversy surrounding the role of interstitial cells of Cajal (ICC) in nitrergic neurotransmission to gastrointestinal smooth muscle, circular smooth muscle from the lower esophageal sphincter (LES) of W/W(v) wild-type and mutant (ICC-deficient) mice were studied by using intracellular and tension recordings in vitro. Resting membrane potential was more negative, and the spontaneous unitary potentials diminished in mutant mice. In wild-type mice, nerve stimulation induced a biphasic inhibitory junction potential (IJP) consisting of a fast initial IJP followed by a long-lasting slow IJP (LSIJP). The IJP was markedly impaired in a significant proportion of mutant mice, whereas in others it was normal. Pharmacological studies in the mice with markedly impaired IJPs revealed that cholinergic and purinergic components of the nerve-mediated responses appeared intact. In wild-type mice, caffeine hyperpolarized smooth muscle cells, inhibited the initial fast IJP, and completely abolished the LSIJP. In mutant mice, caffeine depolarized smooth muscle cells and abolished the impaired LSIJP but did not affect the initial fast IJP. Immunohistochemical staining for c-Kit confirmed deficiency of ICC in mutant mice with a normal nitrergic IJP. Rings of LES circular smooth muscle from W/W(v) mutant mice generated significantly less spontaneous tone than controls. When tone was restored with carbachol, normal nitrergic LES relaxation was recorded. These data suggest that 1) there is significant variability in the generation of nitrergic neurotransmission in the LES of W/W(v) mutant mice, whereas purinergic and cholinergic neurotransmission are intact; 2) the altered nitrergic responses appear to be associated with abnormal Ca2+-dependent signaling initiated by spontaneous Ca2+ release from sarcoplasmic reticulum in smooth muscle cells; and 3) c-Kit-positive ICC are not essential for nitrergic neurotransmission in mouse LES smooth muscle.

TREK-1 channels do not mediate nitrergic neurotransmission in circular smooth muscle from the lower oesophageal sphincter.

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.

Access to specialist gastroenterology care in Canada: comparison of wait times and consensus targets.

BACKGROUND: Monitoring wait times and defining targets for care have been advocated to improve health care delivery related to cancer, heart, diagnostic imaging, joint replacements and sight restoration. There are few data on access to care for digestive diseases, although they pose a greater economic burden than cancer or heart disease in Canada. The present study compared wait times for specialist gastroenterology care with recent, evidence-based, consensus-defined benchmark wait times for a range of digestive diseases. METHODS: Total wait times from primary care referral to investigation were measured for seven digestive disease indications by using the Practice Audit in Gastroenterology program, and were benchmarked against consensus recommendations. RESULTS: Total wait times for 1903 patients who were undergoing investigation exceeded targets for those with probable cancer (median 26 days [25th to 75th percentiles eight to 56 days] versus target of two weeks); probable inflammatory bowel disease (101 days [35 to 209 days] versus two weeks); documented iron deficiency anemia (71 days [19 to 142 days] versus two months); positive fecal occult blood test (73 days [36 to 148 days] versus two months); dyspepsia with alarm symptoms (60 days [23 to 140 days] versus two months); refractory dyspepsia without alarm symptoms (126 days [42 to 225 days] versus two months); and chronic constipation and diarrhea (141 days [68 to 264 days] versus two months). A minority of patients were seen within target times: probable cancer (33% [95% CI 20% to 47%]); probable inflammatory bowel disease (12% [95% CI 1% to 23%]); iron deficiency anemia (46% [95% CI 37% to 55%]); positive occult blood test (41% [95% CI 28% to 54%]); dyspepsia with alarm symptoms (51% [95% CI 41% to 60%]); refractory dyspepsia without alarm symptoms (33% [95% CI 19% to 47%]); and chronic constipation and diarrhea (21% [95% CI 14% to 29%]). DISCUSSION: Total wait times for the seven indications exceeded the consensus targets; 51% to 88% of patients were not seen within the target wait time. Multiple interventions, including adoption of evidence-based management guidelines and provision of economic and human resources, are needed to ensure appropriate access to digestive health care in Canada. Outcomes can be evaluated by the 'point-of-care', practice audit methodology used for the present study.

Regional differences in nitrergic innervation of the smooth muscle of murine lower oesophageal sphincter.

BACKGROUND AND PURPOSE: Anatomical and pharmacological studies have demonstrated that the lower oesophageal sphincter (LES) is not a simple homogenous circular muscle with uniform innervation. Regional differences have been demonstrated in several species including humans. We investigated, for the first time in mice LES, regionally distinct physiological and pharmacological characteristics of the neuromusculature. EXPERIMENTAL APPROACH: Conventional intracellular recordings and pharmacological techniques were employed to evaluate electrical properties and functional innervation of smooth muscle cells. Results from CD1 (control), nNOS((-/-)) and eNOS((-/-)) genetic knockout mice were compared. KEY RESULTS: Smooth muscle of sling and clasp LES displayed unitary membrane potentials of 1- 4 mV. Transmural nerve stimulation produced a monophasic inhibitory junction potential (IJP) in the sling, whereas in the clasp a biphasic IJP, consisting of a brief IJP followed by a long-lasting slow IJP (lsIJP), was induced. Pharmacological interventions and genetically modified mice were used to demonstrate a monophasic apamin-sensitive (purinergic) component in both LES regions. However, the nitrergic IJP was monophasic in the sling and biphasic in the clasp. Unitary membrane potentials and IJPs were not different in CD1 and eNOS((-/-)) mice, suggesting no involvement of myogenic NOS. CONCLUSION AND IMPLICATIONS: These data in mouse LES indicate that there are previously unreported regional differences in the IJP and that both the apamin-resistant monophasic and biphasic IJPs are mediated primarily by nitrergic innervation.

Role of platelet-activating factor in acid-induced esophageal mucosal injury.

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.

Role of cADPR in sodium nitroprusside-induced opossum esophageal longitudinal smooth muscle contraction.

Nitric oxide (NO) relaxes most smooth muscle, including the circular smooth muscle (CSM) of the esophagus, whereas in the adjacent longitudinal smooth muscle (LSM), it causes contraction. The second messenger pathways responsible for this NO-induced LSM contraction are unclear, given that these opposing effects of NO are both cGMP dependent. In intestinal LSM, but not CSM, cADP ribose (cADPR)-dependent pathways participate in Ca(2+) mobilization and muscle contraction; whether similar differences exist in the esophagus is unknown. The purpose of this study was to determine whether cADPR plays a role in the NO-mediated contraction of opossum esophageal LSM. Standard isometric tension recordings were performed using both LSM and CSM strips from opossum distal esophagus that were hung in 10-ml tissue baths perfused with oxygenated Krebs solution. cADPR produced concentration-dependent contraction of LSM strips with an EC(50) of 1 nM and peak contraction of 57 +/- 18% of the 60 mM KCl-induced contraction. cADPR had no effect on CSM strips at concentrations up to 10(-6) M. The EC(50) of cADPR caused contraction (18 +/- 2% from initial resting length) of isolated LSM cells. Sodium nitroprusside (SNP; 300 muM) induced contraction of LSM strips that averaged 67 +/- 5% of the KCl response. cADPR antagonists 8-bromo-cADPR and 8-amino-cADPR, as well as ryanodine receptor antagonists ryanodine and tetracaine, significantly inhibited the SNP-induced contraction. In conclusion, in the opossum esophagus, 1) cADPR induces contraction of LSM, but not CSM, and 2) NO-induced contraction of LSM appears to involve a cADPR-dependent pathway.

Clinical diagnosis of achalasia: how reliable is the barium x-ray?

Manometry is considered to be the gold standard for the diagnosis of achalasia. However, many physicians believe that contrast radiography, classically showing esophageal dilation with bird-beak narrowing of the gastroesophageal junction, is also accurate in either diagnosing or excluding the disorder. The aim of the current study was to determine the accuracy of barium x-ray in the diagnosis of achalasia. The radiological diagnosis of all patients manometrically diagnosed with achalasia (using conventional criteria) between January 1994 and June 1998 were reviewed. A total of 51 cases of achalasia were identified. Thirteen patients were excluded because they either did not have contrast radiography before a manometric diagnosis or had their x-rays performed more than six months previously. Of the remaining 38 patients, achalasia was stated as a diagnostic possibility in the radiologists report in only 22 (58%) of those patients. Achalasia was not considered in the remaining 16 patients: two were reported as normal, four as having stenosis/narrowing in distal esophagus, two as having presbyesophagus, one as having mild gastroesophageal reflux and seven as having nonspecific dysmotility. To determine the reason for the diagnostic failure of the barium x-ray, an expert gastrointestinal radiologist reviewed 12 of the nondiagnostic x-rays in a blinded fashion, interspersed with 10 randomly selected esophageal-contrast radiographs from control subjects to avoid bias. Of these initially nondiagnostic x-rays in achalasia patients, typical radiological features of achalasia were deemed to be present in 50%. The present study indicates that contrast radiography lacks sensitivity in the diagnosis of achalasia. This is not only due to radiologist oversight but also because of the absence of the characteristic radiological features in many cases. This reinforces the important role of esophageal manometry in patients with persistent nonstructural dysphagia.

Effects of acid-induced esophagitis on esophageal smooth muscle.

Acid-induced esophagitis is associated with sustained longitudinal smooth muscle (LSM) contraction and consequent esophageal shortening. In addition, LSM strips from opossums with esophagitis are hyper-responsive, while the circular smooth muscle (CSM) contractility is impaired. To determine the origin of these changes, studies were performed on esophageal smooth muscle cells isolated from opossum esophagi perfused intraluminally on 3 consecutive days with either saline (control; n = 8) or HCl (n = 9). CSM and LSM cells, obtained by enzymatic digestion, were exposed to various concentrations of carbachol (CCh) and fixed. CCh induced concentration-dependent contraction of both LSM and CSM cells. CCh-induced LSM cell contraction was not different between control and esophagitis animals; however, there was marked attenuation in the CCh-induced contraction of CSM cells from esophagitis animals. Morphological studies revealed significant hypertrophy of the CSM cells. These findings suggest that impaired CSM contractility can be attributed at least in part to alterations to the CSM cell itself. In contrast, hyper-contractility demonstrated in LSM strips is likely related to factors in the surrounding tissue.

Nitric oxide contracts longitudinal smooth muscle of opossum oesophagus via excitation-contraction coupling.

1. The effects of sodium nitroprusside (SNP) and diethylenetriamine/nitric oxide adduct (DETA/NO), putative nitric oxide (NO) donors, on opossum oesophageal longitudinal smooth muscle were investigated using isometric tension and intracellular micro-electrode recordings. 2. SNP produced concentration-dependent contractions of oesophageal longitudinal smooth muscle with an EC(50) of 239.6 +/- 78.2 microM (mean +/- S.E.M., n = 10). Maximal contraction induced by SNP (1 mM) was about 75.5 +/- 8.5 % (n = 10) of the 60 mM KCl-induced contraction. The SNP-induced contraction was resistant to tetrodotoxin (TTX; 1 microM), but abolished by nifedipine (1 microM), as well as by niflumic acid (300 microM) and 9-anthroic acid (9-AC; 1 mM), Ca(2+)-activated Cl(-) channel blockers. 3. DETA/NO at concentrations of 100 and 500 microM induced 83.1 +/- 24.4 and 104.1 +/- 34.9 % of the 60 mM KCl-induced contraction (n = 4), respectively, which was abolished by nifedipine (1 microM), niflumic acid (300 microM) and 9-AC (1 mM). 4. Pre-application of 1H-[1,2,4]oxidiazolo[4,3,-alpha]quinoxalin-1-one (ODQ) (10 microM), a guanylate cyclase inhibitor, significantly inhibited the SNP-induced contraction, whereas 8-bromo-cGMP (1 mM), a membrane-permeable analogue of cGMP, mimicked the SNP-induced contraction. 5. Intracellular recordings revealed that SNP (300 microM) depolarized resting membrane potentials (RMPs) and increased the frequency of spontaneous spike-like action potentials. However, these electrical alterations were eliminated by pretreatment with niflumic acid (300 microM). 6. These results suggest that NO produces an excitation-contraction coupling in opossum oesophageal longitudinal smooth muscle via a cGMP-dependent signalling pathway. This contraction depends on extracellular Ca(2+) entry through activation of L-type Ca(2+) channels.

Diversity of K+ channels in circular smooth muscle of opossum lower esophageal sphincter.

We previously demonstrated that a balance of K+ and Ca2+-activated Cl- channel activity maintained the basal tone of circular smooth muscle of opossum lower esophageal sphincter (LES). In the current studies, the contribution of major K+ channels to the LES basal tone was investigated in circular smooth muscle of opossum LES in vitro. K+ channel activity was recorded in dispersed single cells at room temperature using patch-clamp recordings. Whole-cell patch-clamp recordings displayed an outward current beginning to activate at -60 mV by step test pulses lasting 400 ms (-120 mV to +100 mV) with increments of 20 mV from holding potential of -80 mV ([K+]I = 150 mM, [K+]o = 2.5 mM). However, no inward rectification was observed. The outward current peaked within 50 ms and showed little or no inactivation. It was significantly decreased by bath application of nifedipine, tetraethylammonium (TEA), 4-aminopyridine (4-AP), and iberiotoxin (IBTN). Further combination of TEA with 4-AP, nifedipine with 4-AP, and IBTN with TEA, or vice versa, blocked more than 90% of the outward current. Ca2+-sensitive single channels were recorded at asymetrical K+ gradients in cell-attached patch-clamp configurations (100.8+/-3.2 pS, n = 8). Open probability of the single channels recorded in inside-out patch-clamp configurations were greatly decreased by bath application of IBTN (100 nM) (Vh = -14.4+/-4.8 mV in control vs. 27.3+/-0.1 mV, n = 3, P < 0.05). These data suggest that large conductance Ca2+-activated K+ and delayed rectifier K+ channels contribute to the membrane potential, and thereby regulate the basal tone of opossum LES circular smooth muscle.

Role of substance P and calcitonin gene-related peptide in acid-induced augmentation of opossum esophageal blood flow.

Increased esophageal blood flow may protect against damaging refluxed gastric juices. We have shown that mast cells, histamine, and nitric oxide increase esophageal blood flow in the opossum during acid perfusion. This study examined the roles of substance P and calcitonin gene-related peptide on acid-induced hyperemia and whether the effects of substance P are mediated by mast cells. The opossum distal esophagus was perfused with saline, acid, or capsaicin while blood flow and histamine release were determined. Neuropeptides and neurokinin antagonists were administered parenterally. Only acid or calcitonin gene-related peptide (not substance P or capsaicin) significantly increased blood flow, which was prevented by neurokinin or calcitonin-gene-related peptide antagonists. Acid, substance P, and capsaicin all increased histamine release. Pretreatment with neurokinin antagonists did not affect acid-induced histamine release. We conclude that calcitonin-gene-related peptide is an important mediator of acid-induced esophageal hyperemia, while substance P plays an indirect role.

Impairment of deglutition reflex by acid-induced esophageal mucosal injury.

Swallowing is an important defense mechanism against reflux esophagitis as it helps clear refluxed gastric contents from the esophagus, while bicarbonate in the saliva acts to neutralize acid. The purpose of the present study was to examine the effect of esophagitis on the deglutition reflex in anesthetized opossums. Animals perfused with either an acidified pepsin solution for 45 min or with 100 mM hydrochloric acid for 45 min on each of three consecutive days exhibited a significantly impaired deglutition reflex in comparison to baseline. Control animals perfused with 0.9% saline showed no impairment. Bilateral cervical vagotomy in animals perfused with acidified pepsin attenuated the impaired deglutition reflex. Taken together, these results suggest that esophagitis causes an impairment in the deglutition reflex that is mediated by vagal afferent pathways.

Etiology and pathogenesis of achalasia.

The primary pathophysiologic abnormality in achalasia is loss of intrinsic inhibitory innervation of the lower esophageal sphincter and smooth muscle segment of the esophageal body. Disease of the extrinsic (vagal) nervous system and esophageal musculature may also be present, but these are less consistent findings and could represent secondary phenomena. Inflammation within the esophageal myenteric plexus is pathognomonic of the disease, but the cause of this inflammation is uncertain. Autoimmunity and previous viral infection have been hypothesized, but remain unproven.