Measurement of bicarbonate output from the intact human oesophagus

Characterization of oncocytes in deep esophageal glands

Deep esophageal glands play a vital role in the protection and regeneration of the esophageal mucosa. Conditions such as gastroesophageal reflux disease and Barrett's esophagus have been associated with a change in the usual glands by oncocytic metaplasia. However, little is known regarding the function of oncocytes or the relevance of this metaplastic change in the human esophagus. We hypothesized that oncocytes of deep esophageal glands also express markers characteristic of a ductal epithelial phenotype because similar oncocytes have been described as part of large ductal epithelial cells in salivary glands. We used immunohistochemical stains to define structural, functional, proliferative, and potential stem/progenitor characteristics of oncocytes. Oncocytes did not express mucins or lysozyme C, two molecules found in mucous cells and used for antimicrobial defense. Oncocytes did not express CK5, a cytokeratin found in myoepithelial cells and basal epithelial cells, but expressed CK7, a cytokeratin found in intralobular ductal epithelial cells and luminal epithelial cells of the main duct. Oncocytes expressed cystic fibrosis transmembrane conductance regulator and sodium/potassium ATPase, ion channels that play a role in bicarbonate secretion. Membrane-bound beta-catenin was detected in oncocytes, but these cells did not express the proliferative marker Ki67. Approximately, a third of oncocytes expressed SOX9 and p63, transcription factors expressed in epithelial progenitor cells in multiple organs. Moreover, oncocytes expressed CD44, a transmembrane Glycoprotein expressed in cancer stem cells. Taken together, our data show that oncocytes express markers of intralobular ductal epithelial cells and luminal epithelial cells of the main duct. Additionally, our observations suggest that oncocytes act as epithelial progenitor cells and play a role in bicarbonate secretion. Since oncocytic metaplasia is associated with conditions of chronic acid injury, it is possible that oncocytes replace the mucous cells in deep esophageal glands (dEG) as an adaptive change to counteract injury from acid reflux. The marker characterization suggests that oncocytes may originate from transdifferentiation of myoepithelial and mucous cells. This transdifferentiation might lead to an overall decrease of mucins production and secretion by the dEG and a subsequent reduction of the protection conferred by the viscoelastic mucous layer.

Distal esophageal acid exposure and esophageal motility in patients with mild reflux esophagitis or non-erosive reflux disease

AIM: To investigate the characteristics of and changes in distal esophageal acid exposure and esophageal motility in patients with mild reflux esophagitis (RE) or non-erosive reflux disease (NERD) by performing esophageal PH monitoring and manometry.

METHODS: Thirty RE patients (16 LA-A cases and 14 LA-B cases) and 16 NERD patients who were diagnosed according to the Los Angeles classification criteria and 10 healthy subjects were recruited in our study, all of whom received 24-h esophageal PH monitoring and esophageal manometry.

RESULTS: DeMeester scores of the LA-A, LA-B and NERD groups were significantly higher than that of the control group. Although there was no difference in DeMeester score between the LA-A group and NERD group, the upright acid exposure time and the number of long reflux periods in the latter group were dramatically increased. Significantly higher DeMeester score was seen in the LA-B group than in the LA-A and NERD groups. All variables of 24-h esophageal PH monitoring were significantly different between the LA-A and LA-B groups. No differences in the lower esophageal sphincter pressure (LESP) and peristaltic amplitude (PA) of esophageal body were observed among the LA-A, NERD and control groups, though PA showed a tendency to increase in the distal esophagus in the former two groups. LESP in the LA-B group was lower than that in other groups. In addition, the LA-B group had a lower PA in the distal esophagus than the LA-A group. The number of ineffective esophageal motility (IEM) in the RE group was obviously elevated in comparison to the control group.

CONCLUSION: There is a difference in acid exposure of the distal esophagus between patients with mild RE (LA-B) and those with NERD. DeMeester score, LES dysfunction and esophageal peristaltic dysfunction positively correlate with the severity of RE. LES dysfunction and esophageal peristaltic dysfunction may not be the major pathogenic factors for RE (LA-A) or NERD. IEM is the primary motility disorder of reflux esophagitis.

Oesophageal sensation in response to high PCO(2) and acidic solutions in nonerosive reflux disease

BACKGROUND

Heartburn is commonly associated with the presence of acid in the oesophageal lumen. However, in patients with nonerosive reflux disease (NERD), the mechanism by which acid traverses the mucosa is not clear. We hypothesized that the luminal acid signal traverses the oesophageal epithelium in the form of the highly permeant gas CO(2) , which then is reconverted to H(+) in the submucosa.

MATERIALS AND METHODS

  Ten patients with heartburn, normal upper endoscopy and increased oesophageal acid exposure (NERD patients) and 10 healthy subjects were enrolled. Perceptual responses to intraoesophageal acid (0·1 N HCl solution) and a high PCO(2) solution were determined using a randomized cross over design. Stimulus-response functions to perfusions were quantified by three parameters: lag time to symptom perception, intensity rating and perfusion sensitivity score.

RESULTS

 In NERD patients, the difference in lag time to typical symptom perception, intensity rating and perfusion sensitivity score between high PCO(2) and acid perfusions was statistically significant (P = 0·02, 0·01 and 0·02, respectively). However, the difference in the same perfusion parameters between acid and high PCO(2) perfusions was nonsignificant in healthy controls. When NERD and controls were compared, the difference between the different perfusion variables was nonsignificant (adjusted to age).

CONCLUSIONS

In NERD subjects, acid perfusion reliably evoked heartburn symptoms of greater intensity than in healthy controls. Nevertheless, a high PCO(2) perfusion failed to produce symptoms in either group.

Effect of various test meals on gastric and jejunal carbon dioxide: A study in healthy subjects

OBJECTIVE

The normal pattern of carbon dioxide (CO2) levels in the human stomach and small bowel after meals is unknown. The intraluminal carbon dioxide level is a sensitive and early marker for organ mucosal ischemia. CO2 levels in both the stomach and small bowel are influenced by multiple factors other than adequacy of perfusion. Gastric acid production, salivary bicarbonate and CO2 produced or absorbed by meals are the disturbing variables. Prolonged gastric (and jejunal) tonometry after meals can be of additional value in the work-up of patients suspected of (chronic) gastrointestinal ischemia. The purpose of this study was to challenge these problems using in vitro tested meals and a rigid acid-suppression regimen in a group of healthy subjects.

MATERIAL AND METHODS

Standard meals were tested in vitro on the ability to produce and buffer CO2. Meals with the least CO2 variations were subsequently used in healthy subjects. Tonometry of the stomach and jejunum was performed for 24 h, with optimal and controlled acid suppression.

RESULTS

Ten subjects were enrolled in the study. Acid production was sufficiently suppressed. The gastric PCO2 baseline (fasting) was 6.5 (1.0), and significantly lower than the jejunum PCO2 baseline of 7.6 (0.9) kPa. The gastric baseline during the day was 6.9 (1.6), and significantly lower than the gastric baseline during the night of 8.0 (1.8), suggesting a diurnal variation of PCO2. Increases in PCO2 levels were seen in all subjects, after meals and between meals.

CONCLUSIONS

Prolonged gastric and jejunal tonometry is feasible in humans. PCO2 levels were seen to peak after, but also in-between, most meals. The diurnal variation in PCO2 might reflect reversible gastric mucosal ischemia.

Effect of topical esophageal acidification on salivary secretion: identification of the mechanism of action

BACKGROUND

In past studies, investigators have reported that the salivary glands respond to esophageal acidification by increased salivary secretion and termed this response the 'esophago-salivary response'. The existence, however, of such a reflex was but a speculation because the verification of its mechanism could not be traced in the literature. In the current study, the hypothesis that the salivary glands' response to esophageal acidification is a reflex was investigated.

METHODS

In 15 healthy volunteers (nine men, six women, age 32.3 +/- 4.2 years) the saliva of the four salivary glands was collected by intubation after individual esophageal perfusion with normal saline and 100 mmol HCl. The test was repeated after each of the lower esophagus and the salivary glands had been separately anesthetized. The latency was calculated.

RESULTS

The mean basal volume of saliva was 62.7 +/- 6.4 mL/60 min. This volume did not show a significant change (P > 0.05) on esophageal saline instillation, whereas acid perfusion effected a significant increase (P < 0.01). The mean latency was 12.4 +/- 2.7 s. Esophageal acid perfusion after lower esophageal anesthetization did not produce a significant change in salivary volume; similar results were obtained on repetition of the test after anesthetization of salivary glands. When saline was used instead of lidocaine in the lower esophagus or salivary glands, the salivary glands' response was similar to that without saline perfusion.

CONCLUSION

Esophageal acidification effected an increase of secreted saliva which clears the esophagus of the refluxed acid. Increased salivation on esophageal acidification is suggested to be a reflex and is mediated through the 'esophago-salivary' reflex. This reflex might be of diagnostic significance in the investigation of reflux esophagitis, a point that requires further study.

HCO3- secretion in the esophageal submucosal glands

The mammalian esophagus has the capacity to secrete a HCO(3)(-) and mucin-rich fluid in the esophageal lumen. These secretions originate from the submucosal glands (SMG) and can contribute to esophageal protection against refluxed gastric acid. The cellular mechanisms by which glandular cells achieve these secretions are largely unknown. To study this phenomenon, we used the pH-stat technique to measure luminal alkali secretion in an isolated, perfused pig esophagus preparation. Immunohistochemistry was used to localize receptors and transporters involved in HCO(3)(-) transport. The SMG-bearing esophagus was found to have significant basal alkali secretion, predominantly HCO(3)(-), which averaged 0.21 +/- 0.04 microeq.h(-1).cm(-2). This basal secretion was doubled when stimulated by carbachol but abolished by HCO(3)(-) or Cl(-) removal. Basal- and carbachol-stimulated secretions were also blocked by serosal application of atropine, pirenzipine, DIDS, methazolamide, and ethoxzolamide. The membrane-impermeable carbonic anhydrase inhibitor benzolamide, applied to the serosal bath, partially inhibited basal HCO(3)(-) secretion and blocked the stimulation by carbachol. Immunohistochemistry using antibodies to M(1) cholinergic receptor or carbonic anhydrase-II enzyme showed intense labeling of duct cells and serous demilunes but no labeling of mucous cells. Labeling with an antibody to Na(+)-(HCO(3)(-))(n) (rat kidney NBC) was positive in ducts and serous cells, whereas labeling for Cl(-)/HCO(3)(-) exchanger (AE2) was positive in duct cells but less pronounced in serous cells. These data indicate that duct cells and serous demilunes of SMG play a role in HCO(3)(-) secretion, a process that involves M(1) cholinergic receptor stimulation. HCO(3)(-) transport in these cells is dependent on cytosolic and serosal membrane-bound carbonic anhydrase. HCO(3)(-) secretion is also dependent on serosal Cl(-) and is mediated by DIDS-sensitive transporters, possibly NBC and AE2.

Cell biology of laryngeal epithelial defenses in health and disease: preliminary studies

Esophageal epithelium has intrinsic antireflux defenses, including carbonic anhydrases (CAs I to IV) that appear to be protective against gastric reflux. This study aimed to investigate the expression and distribution of CA isoenzymes in laryngeal epithelium. Laryngeal biopsy specimens collected from the vocal fold and interarytenoid regions were analyzed by Western blotting and immunofluorescence. Carbonic anhydrases I and II were expressed by the majority of samples analyzed. In contrast, CA III was differentially expressed in the interarytenoid samples and was not detected in any vocal fold samples. The expression of CA III was increased in esophagitis as compared to normal esophageal tissue. Carbonic anhydrase I and III isoenzymes were distributed cytoplasmically in the basal and lower prickle cell layers. The laryngeal epithelium expresses some CA isoenzymes and has the potential to protect itself against laryngopharyngeal reflux. Laryngeal tissue may be more sensitive to injury due to reflux damage than the esophageal mucosa because of different responses of CA isoenzymes.

Esophageal mucin: an adherent mucus gel barrier is absent in the normal esophagus but present in columnar-lined Barrett's esophagus

OBJECTIVES

The presence of a protective adherent mucus gel barrier against gastric reflux in the healthy esophagus is uncertain. The aim was to characterize the surface mucin composition and determine the extent of any adherent mucus gel layer on the normal esophagus, and compare this with that in Barrett's esophagus.

METHODS

Isolated surface mucins were characterized by density centrifugation, gel filtration chromatography, and chemical composition. Adherent surface mucus was visualized in situ on unfixed and cryostat sections of mucosa and biopsies using a method that preserves mucus layer thickness.

RESULTS

There was a complete absence of adherent mucus gel layers on normal human, pig, and rat esophagi. This was in contrast to the thick adherent mucous layer (median thickness = 100-200 microm) seen on the corresponding gastric mucosa. Small quantities of glycoprotein with a composition characteristic of a secretory mucin were isolated from the pig esophagus surface. The mucin, density range between 1.44 and 1.48 g x ml(-1), contained 80% carbohydrate and was rich in serine, threonine, and proline. The mucin fragmented into smaller glycoprotein units on proteolysis and partially on reduction. Cryostat sections from columnar-lined esophageal biopsies had a substantial adherent surface mucous layer (median thickness = 90 microm, interquartile range = 84-94 microm) staining for neutral mucins (gastric-type epithelium) and acidic mucins (intestinal metaplasia).

CONCLUSIONS

A secretory mucin, with an analysis distinct from that of gastric or salivary mucin, is present in very small quantities on the esophageal mucosa and in amounts insufficient to form an adherent gel layer. It is unlikely that mucus has a role in protecting the normal esophagus against reflux. However, an adherent mucous layer was observed over columnar-lined esophagus, and this may protect against reflux.

Review article: alginate-raft formulations in the treatment of heartburn and acid reflux

Alginate-based raft-forming formulations have been marketed word-wide for over 30 years under various brand names, including Gaviscon. They are used for the symptomatic treatment of heartburn and oesophagitis, and appear to act by a unique mechanism which differs from that of traditional antacids. In the presence of gastric acid, alginates precipitate, forming a gel. Alginate-based raft-forming formulations usually contain sodium or potassium bicarbonate; in the presence of gastric acid, the bicarbonate is converted to carbon dioxide which becomes entrapped within the gel precipitate, converting it into a foam which floats on the surface of the gastric contents, much like a raft on water. Both in vitro and in vivo studies have demonstrated that alginate-based rafts can entrap carbon dioxide, as well as antacid components contained in some formulations, thus providing a relatively pH-neutral barrier. Several studies have demonstrated that the alginate raft can preferentially move into the oesophagus in place, or ahead, of acidic gastric contents during episodes of gastro-oesophageal reflux; some studies further suggest that the raft can act as a physical barrier to reduce reflux episodes. Although some alginate-based formulations also contain antacid components which can provide significant acid neutralization capacity, the efficacy of these formulations to reduce heartburn symptoms does not appear to be totally dependent on the neutralization of bulk gastric contents. The strength of the alginate raft is dependant on several factors, including the amount of carbon dioxide generated and entrapped in the raft, the molecular properties of the alginate, and the presence of aluminium or calcium in the antacid components of the formulation. Raft formation occurs rapidly, often within a few seconds of dosing; hence alginate-containing antacids are comparable to traditional antacids for speed of onset of relief. Since the raft can be retained in the stomach for several hours, alginate-based raft-forming formulations can additionally provide longer-lasting relief than that of traditional antacids. Indeed, clinical studies have shown Gaviscon is superior to placebo, and equal to or significantly better than traditional antacids for relieving heartburn symptoms. Alginate-based, raft-forming formulations have been used to treat reflux symptoms in infants and children, and in the management of heartburn and reflux during pregnancy. While Gaviscon is effective when used alone, it is compatible with, and does not interfere with the activity of antisecretory agents such as cimetidine. Even with the introduction of new antisecretory and promotility agents, alginate-rafting formulations will continue to have a role in the treatment of heartburn and reflux symptoms. Their unique non-systemic mechanism of action provides rapid and long-duration relief of heartburn and acid reflux symptoms.

Esophageal submucosal glands: structure and function

A three-tiered defense system exists in the esophagus, which serves a dual purpose of both limiting the degree of gastroesophageal reflux and minimizing the risk of acid-induced mucosal injury. The antireflux barrier, composed of both the lower esophageal sphincter and the diaphragmatic pinchcock, is the first line of defense and serves to limit the frequency and volume of refluxed gastric contents. When the antireflux barrier fails, the second line of defense, esophageal clearance, comes into play and serves to limit the duration of contact between gastric contents and the esophageal epithelium. Mechanisms involved in esophageal clearance include gravity and esophageal peristalsis, which remove volume, and secretions from swallowed saliva and esophageal submucosal glands, which neutralize acid. The third line of defense, tissue resistance, is necessary when acid contact time is prolonged such as when esophageal clearance is either ineffective or not operative (e.g., during sleep). Most studies that have examined esophageal clearance mechanisms have focused on the roles of esophageal peristalsis and salivary secretion, but the role of submucosal gland secretions is less well understood. This article reviews the structure and function of esophageal submucosal glands and discusses the potential role of their secretory products in esophageal clearance and tissue resistance.

Manometric study of hiatal hernia and its correlation with esophageal peristalsis

The pathogenesis of gastroesophageal reflux disease (GERD) is considered multifactorial, but alterations of the esophagogastric junction (EGJ) and hiatal hernia play a prominent role. The correlations between hiatal hernia and the other pathogenetic factors are as yet unclear, and they need to be investigated by a methodological approach based on new anatomic and functional criteria. Our aim was to study, by stationary manometry, the relationships between small reducible hiatal hernia, identified by endoscopy, and esophageal peristalsis, in patients with and without GERD. According to the absence or presence of esophagitis (E), and the absence or presence of hiatal hernia (H), 58 subjects were divided into four groups: controls 10; H 14; E 10; and HE 24. Stationary manometry was performed by the rapid pull-through (RPT) technique, with catheter water perfused, to study the lower esophageal high pressure zone [lower esophageal sphincter (LES) and diaphragmatic crura] and the parameters of esophageal peristalsis. In patients with hiatal hernia, the various combinations of peak and/or deflection of manometric line pressure identified five EGJ profiles, only one of which reveals (by one-peak profile due to superimposed LES and diaphragmatic crura) the reducibility of the hernia. The frequency of the five profiles was calculated in the HE and H groups: a two-peak profile was significantly more prevalent in these patients, although less so in the group with esophagitis. In E patients the distal amplitude and the distal propagation of esophageal waves were significantly lower than in the other three groups (P < 0.05 vs controls and group HE; P < 0.01 vs group H). Furthermore, the distal amplitude was significantly higher in the group H than in the HE (P < 0.01). Our results show a better definition of hiatal hernia morphology, via the RPT technique, disclosing five pressure profiles. In addition, a significant link was found between small reducible hiatal hernia without GERD and wave amplitude of the distal esophagus. The amplification of peristaltic clearing may be considered the initial protective process against acid reflux; the breakdown of this mechanism may trigger the pathological sequence of GERD.

Intraesophageal pH monitoring during acid infusion in patients with systemic sclerosis

Incidental clinical observations suggest that buffering substances may accumulate in the distal esophagus of patients with systemic sclerosis. The aim of our study was to assess if the buffering capacity of the intraesophageal milieu is increased in patients with systemic sclerosis and if this effect can be correlated to some pathophysiological aspects of the disease. We recorded intraesophageal pH before and during a 10-min intraesophageal infusion of acid (HCl 0.01 N, 1 ml/min), as well as esophageal motility and clearance function, in 16 patients with systemic sclerosis and 10 healthy subjects. Esophageal buffering capacity expressed as the area under the curve of intraesophageal pH during acid infusion was significantly higher in the patients than in the controls, and this variable was directly correlated with esophageal clearing time. In conclusion, esophageal buffering capacity is increased in patients with systemic sclerosis and is possibly the consequence of the accumulation of buffering substances in the distal esophagus.

Oesophageal epithelial innervation in health and reflux oesophagitis

BACKGROUND

The response of the oesophagus to refluxed gastric contents is likely to depend on intact neural mechanisms in the oesophageal mucosa. The epithelial innervation has not been systematically evaluated in health or reflux disease.

AIMS

To study oesophageal epithelial innervation in controls, and also inflamed and non-inflamed mucosa in patients with reflux oesophagitis and healed oesophagitis.

PATIENTS

Ten controls, nine patients with reflux oesophagitis, and five patients with healed oesophagitis.

METHODS

Oesophageal epithelial biopsy specimens were obtained at endoscopy. The distribution of the neuronal marker protein gene product 9.5 (PGP), and the neuropeptides calcitonin gene related peptide (CGRP), neuropeptide Y (NPY), substance P (SP), and vasoactive intestinal peptide (VIP) were investigated by immunohistochemistry. Density of innervation was assessed by the proportion of papillae in each oesophageal epithelial biopsy specimen containing immunoreactive fibres (found in the subepithelium and epithelial papillae, but not penetrating the epithelium).

RESULTS

The proportion of papillae positive for PGP immunoreactive nerve fibres was significantly increased in inflamed tissue when compared with controls, and non-inflamed and healed tissue. There was also a significant increase in VIP immunoreactive fibres within epithelial papillae. Other neuropeptides showed no proportional changes in inflammation.

CONCLUSIONS

Epithelial biopsy specimens can be used to assess innervation in the oesophagus. The innervation of the oesophageal mucosa is not altered in non-inflamed tissue of patients with oesophagitis but alters in response to inflammation, where there is a selective increase (about three- to fourfold) in VIP containing nerves.

Reappraisal of bicarbonate secretion by the human oesophagus

BACKGROUND AND AIMS

Administration of omeprazole to healthy volunteers was recently reported to increase proximal duodenal mucosal bicarbonate secretion. As human oesophagus also secretes bicarbonate, the hypothesis was tested that omeprazole may stimulate oesophageal bicarbonate secretion and thus contribute to the therapeutic efficacy of the drug in gastro-oesophageal reflux disease.

SUBJECTS AND METHODS

In nine healthy volunteers, oesophageal "steady state" perfusion of a 10 cm open segment of distal oesophagus was performed twice in random order. The volunteers were pretreated with either 60 mg/day omeprazole for three days and 80 mg intravenous omeprazole before perfusion or 600 mg/day ranitidine for three days and 50 mg/h intravenously during the perfusion. Saliva and samples of aspirate from the perfused oesophagus and stomach were collected and bicarbonate concentrations were measured.

RESULTS

The median rates (95% confidence intervals) of intrinsic oesophageal bicarbonate secretion, corrected for contaminating salivary and gastric bicarbonate, were 89 (33-150) and 121 (63-203) mumol/h/10 cm (p > 0.5) in omeprazole and ranitidine treated subjects respectively. Salivary and gastric bicarbonate contaminating the oesophagus accounted for 14% and 3%, respectively, of total oesophageal bicarbonate output.

CONCLUSIONS

Bicarbonate secretory capacity of the human oesophagus is less than previously assumed, and the clinical relevance of intrinsic oesophageal bicarbonate for mucosal defence may be overestimated. As omeprazole and ranitidine did not affect bicarbonate secretion differently there was no evidence that omeprazole acts on bicarbonate secretory cells in the oesophageal mucosa.

Bile in the oesophagus: clinical relevance and ambulatory detection

BACKGROUND

Experimental work in animals has implicated a role for bile in the pathogenesis of several oesophageal mucosal diseases such as oesophagitis, Barrett's oesophagus and oesophageal adenocarcinoma. Recent descriptions of a high incidence of intestinal metaplasia at the gastro-oesophageal junction in patients without a classical 3-cm Barrett's columnar-lined segment, combined with a rising incidence in oesophageal and cardia adenocarcinoma, have stimulated interest in the causes of these conditions.

METHODS AND RESULTS

Animal studies concerned with defining the role of the various gastroduodenal reflux constituents in oesophageal mucosal injury are summarized and evidence for bile in the pathogenesis of Barrett's oesophagus and oesophageal adenocarcinoma is reviewed. The results of various techniques for clinical measurement of oesophageal bile reflux, such as aspiration, scintigraphy and pH monitoring, are evaluated and the significance of recent studies employing ambulatory fibreoptic bilirubin monitoring is discussed.

CONCLUSION

There seems little doubt that bile plays a significant role in oesophageal mucosal disease, in synergy with other constituents of reflux. Although ambulatory bilirubin monitoring is new, some intriguing findings have been reported and it is hoped that this technique will continue to shed light on the role of bile in the oesophagus.

Carbonic anhydrase isoenzymes I, II, III, and IV are present in human esophageal epithelium

Carbonic anhydrase (CA) isoenzymes have been widely studied in the gastrointestinal tract, where they mediate membrane transport events and pH regulation. However, the esophagus has generally received scant attention. In an immunohistochemical study confirmed by Western blotting, we have detected for CA isoenzymes (CAI, II, III, and IV) in the epithelium of human esophagus. Isoenzymes I, III, and sometimes IV (< 10%) were present in the cytoplasm of basal cells and II and IV in the cytoplasm and cell surface membranes, respectively, of suprabasal cells (prickle cells). The localization of CAIV to the plasma membranes was confirmed by electron microscopic immunocytochemistry. CA was effectively divided at the basal-suprabasal interface between low-activity CAI and III (basal) and high-activity CAII and IV (suprabasal). Carbonic anhydrase in esophageal epithelial cells may have several functions: elimination of CO2 and metabolites, participation in membrane transport events during active cell growth, and pH regulation as a protective mechanism against acidic gastric reflux.

Neural influences on human esophageal and salivary alkali secretion

Esophageal secretion HCO3- ions occurs in opossum and man and may contribute to mucosal defense. Using a perfusion technique, neuroregulatory influences on esophageal and salivary HCO3- secretion were investigated in 24 healthy human subjects. The sight and smell of food increased median salivary HCO3- output from 424 to 573 mumol/15 min (P = 0.014), without significantly altering esophageal HCO3- secretion (74-105 mumol/15 min, P = 0.24). Atropine reduced both salivary (610 to 68, 17, 10, and 3 mumol/15 min in successive periods; P < 0.028) and esophageal HCO3- output (108 to 78, 35, 18, and 7 mumol/10 cm/15 min; P < 0.028, respectively. Following atropinization, cholinergic stimulation failed to increase salivary secretion but did "unmask" a small rise in esophageal alkali output (7 to 27 mumol/10 cm/15 min, P = 0.036), implicating a noncholinergic mechanism. Cold-induced pain activated sympathetic reflexes and reduced esophageal HCO3- output (91 to 64 mumol/10 cm/15 min, P = 0.041) without influencing salivary secretion. These observations support a role for the autonomic nervous system in modulating human esophageal and salivary HCO3- secretion.

Carbonic anhydrase is present in human oesophageal epithelium and submucosal glands

Carbonic anhydrase (EC 4.2.1.1) activity was investigated in normal human oesophageal mucosa using the Hansson and Ridderstråle catalytic cobalt methods. The enzyme was detected in the cell membranes and nuclei and, to a lesser extent, in the cytoplasm of the epithelial cells of the mucosa giving a 'chicken wire' appearance. Activity decreased towards the lumen. Other stratified squamous epithelia--buccal mucosa, ectocervix and skin--gave a similar pattern. Acinar cells of oesophageal submucosal glands also exhibited activity for the enzyme, but the ducts did not. The formation of reaction product was prevented by acetazolamide and ethoxzolamide and by the omission of bicarbonate frm the substrate medium. Carbonic anhydrase in oesophageal squamous epithelium may be involved in the control of intra- and extracellular pH, while that in the glands is more likely to be concerned with bicarbonate secretion.

Review article: factors protecting the oesophagus against acid-mediated injury

Reflux of gastric acid and pepsins into the lower oesophagus causes symptoms such as heartburn and nausea, and tissue injury leading to erosive oesophagitis and stricture formation. This article reviews the mechanisms involved in protecting the oesophagus against acid-mediated injury, including the role of the lower oesophageal sphincter, secondary oesophageal peristalsis and swallowed saliva. The oesophageal mucosa has inherent abilities to resist acid damage, and recent data from three laboratories suggest a secretory function with local production of bicarbonate and mucus responsive to local acidification. The evidence for these putative oesophageal defence mechanisms is discussed.

Effect of topical oesophageal acidification on human salivary and oesophageal alkali secretion

Recent human studies suggest that oesophageal HCO3- secretion, in conjunction with salivary HCO3- secretion and secondary oesophageal peristalsis, is important for the protection of oesophageal mucosa from refluxed gastric contents. This study evaluated simultaneously the responsiveness of oesophageal and salivary HCO3- secretion to oesophageal acidification in eight healthy subjects. A 10 cm segment of oesophagus was perfused at a constant rate of 5 ml/min with a specially designed tube assembly. Saline was used initially, and then 10 mM and 100 mM HCl. The perfusates contained 3H-polyethylene glycol (PEG) as a concentration marker to determine volumes. Corrections were applied for a small degree of contamination by swallowed saliva and refluxed gastric alkali. Oesophageal perfusion with 10 mM HCl did not cause symptoms (nausea and heartburn), but tripled the oesophageal HCO3- output from a baseline of 51 mumol/10 cm/10 min (p = 0.021), while doubling the rate of salivary HCO3- secretion from a median basal value of 140 mumol/10 min (p = 0.021). Oesophageal perfusion with 100 mM HCl was associated with symptoms of nausea and heartburn in all subjects. The median oesophageal HCO3- output increased 32 fold to 1659 mumol/10 cm/10 min (interquartile range 569 to 3373; p = 0.036), and salivary HCO3- secretion approximately tripled from basal values (p = 0.036). In conclusion, oesophageal acidification stimulates both salivary and oesophageal HCO3- secretion, responses which may be protective to the oesophageal epithelium.

A histochemical study of carbonic anhydrase in the plasma membranes of human oral epithelial cells

Carbonic anhydrase (EC 4.2.1.1) was detected histochemically from the following regions in patients of various ages (14-84 yr): buccal mucosa, buccal flap, hard palate and tongue. The enzyme was principally located in the cell membranes but was also present in nuclei. There was a gradation in activity from basal (strong) to superficial cells (weak/negative). The carbonic anhydrase inhibitors ethoxyzolamide and acetazolamide abolished activity at 0.001 mM, but were ineffective, even at 1.2 mM, against a reaction associated with the granules of the stratum granulosum. No activity was detected in the absence of bicarbonate from the substrate.

A comparison of membrane enzymes of human and pig oesophagus; the pig oesophagus is a good model for studies of the gullet in man

The distribution and relative catalytic activities of five plasma membrane enzymes (alkaline phosphatase, dipeptidyl peptidase IV, gamma-glutamyl transpeptidase, microsomal alanyl aminopeptidase and glutamyl aminopeptidase) were examined in human and pig oesophagus. In both species, alkaline phosphatase activity occurred in basal and suprabasal cells of the epithelium and in capillaries. Stromal cells in the human submucosa were particularly reactive. Dipeptidyl peptidase IV was present in blood vessels and capillaries in man and pig and in submucous glands in the pig. The enzyme was also present in both species in the lamina propria cells immediately adjacent to the epithelial basal lamina. In the human, gamma-glutamyl transpeptidase occurred in the epithelial basal cells and in isolated basal and lower prickle cells in the pig. Stromal cells in the human submucosa were strongly reactive and capillaries in the muscularis propria in both species moderately active. Microsomal alanyl aminopeptidase was detected in lamina propria cells adjacent to the epithelial basal cell layer in man and pig and at the apices of mucous cells in pig submucous glands. Weak glutamyl aminopeptidase activity was confined to capillaries in both species. The findings of this study, along with the ready availability of pig oesophagus, suggest that the pig may be a suitable model for studies of the gullet in man.