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R C Orlando

Publications and source records attributed to R C Orlando.

At least 37 records · Page 2Linked to original sources
PubMed1998

Review article: oesophageal mucosal resistance.

The human oesophagus is lined by a moist, partially keratinized, stratified squamous epithelium, one important property of which is to serve as a barrier between the outside (luminal) world and the internal world of the organism. This phenomenon in clinical parlance is known as 'oesophageal mucosal resistance'. This article details the structure and functions of the oesophageal mucosa that contribute to its defence against injury upon exposure to refluxed gastric acid.

Esophagus↗
PubMed1998

Luminal hypertonicity and the susceptibility of rabbit esophagus to acid injury.

The esophagus is regularly exposed to hypertonic luminal environments, some of which have the capacity to increase epithelial permeability. The present experiments were designed to determine what impact such environments have on epithelial resistance to injury by acid. Rabbit esophageal epithelium mounted in Ussing chambers was exposed to luminal acid while monitoring electrical resistance (R), a marker of epithelial permeability, and morphology was assessed in tissues luminally pretreated with either urea (1 M), mannitol (1 M), or normal Ringer. Hypertonic mannitol, which had little effect on R, was associated with a minor increase in susceptibility to acid injury, pH 1.6. In contrast, hypertonic urea lowered R and was associated with marked injury upon exposure to acid. This susceptibility to acid injury occurred within 15 minutes of exposure and converted a non-damaging concentration of acid (pH 2.0) to a damaging one. Moreover, urea's effects were abolished if it was removed from the bath allowing R to return to baseline before acidification. We conclude that hypertonic luminal environments that impair epithelial barrier function predispose the esophagus to acid injury. Such findings may provide insight into additional mechanisms contributing to the development of heartburn following meals.

Acid-Base Imbalance↗
PubMed1998

Human esophageal epithelial cells possess an Na+/H+ exchanger for H+ extrusion.

OBJECTIVE: The human esophagus is regularly exposed to refluxed gastric acid. Therefore, its epithelial cells require for survival a means of extruding excess H+ from the cytoplasm. Because Na+/H+ exchange activity has been observed in many mammalian cell types, including that of rabbit esophagus, we sought its presence in human esophageal epithelium. METHODS: Human esophageal epithelial cells derived from endoscopic biopsy specimens or surgical esophagectomy specimens were grown in primary culture and loaded with the fluorescent dye, 2'7'-bis(carboxyethyl)-5(6)-carboxyfluorescein, to monitor intracellular pH (pHi). RESULTS: Resting pHi in bicarbonate-free N'-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid was 7.5 +/- 0.03 (n = 50). Acidification using the NH4Cl prepulse technique lowered pHi by 0.6 +/- 0.02 pH units, with recovery ensuing at an initial rate of 0.09 +/- 0.04 pH units/min. Notably, the rate of recovery was faster the more acidic the pHi, and recovery was abolished by amiloride or replacement with an Na+-free buffer. Acidification by lowering pHo with HCl resulted in a similarly rapid rate of return as with the NH4Cl technique, and resting cells acidified by 0.17 +/- 0.02 pH units/5 min upon exposure to amiloride. CONCLUSIONS: Human esophageal cells possess an H+-extruding mechanism consistent with an Na+/H+ exchanger. This mechanism is active in resting cells, adapts to the degree of pHi lowering, and extrudes H+ efficiently whether loaded by intracellular or extracellular means, making it well suited for epithelial defense against acid injury.

Adult↗
PubMed1998

Effect of ethanol on the structure and function of rabbit esophageal epithelium.

Epidemiological studies indicate a relationship between alcohol consumption and esophageal epithelial disease. We therefore sought the contribution of the direct effects of ethanol on esophageal epithelial structure and (transport and barrier) function. Epithelium from the rabbit was mounted in Ussing chambers and exposed luminally for 1 h to 1-40% ethanol. At concentrations of 1-5% potential difference (PD) increased, and at 10-40% PD decreased. The increase in PD with 1-5% ethanol was accompanied by an increase in short-circuit current (Isc), and this increase in Isc could be blocked by ouabain pretreatment. The decrease in PD with 10-40% ethanol was associated with a decrease in electrical resistance (R), and this decrease in R was paralleled by an increase in transepithelial [14C]mannitol flux. Reversibility of these changes was limited at ethanol concentrations > or = 10%, and these were associated morphologically by patchy or diffuse tissue edema. Moreover, as with ethanol exposure in vitro, exposure in vivo produced dose-dependent changes in PD, Isc, R, and morphology. These observations indicate that exposure to ethanol in concentrations and under conditions reflecting alcohol consumption in humans can alter and impair esophageal epithelial transport and barrier functions. Such impairments are likely to contribute to the observed increase in risk of esophageal disease with regular consumption of alcoholic beverages.

Animals↗
PubMed1997

HCl-induced cell edema in primary cultured rabbit esophageal epithelium.

BACKGROUND & AIMS: In a prior study, esophageal epithelial cells within intact epithelium were observed to swell after exposure to low extracellular pH (pHo) caused by activation of a bumetanide-sensitive NaK2Cl cotransporter. Because these results were obtained by correlation of tissue wet-weight gain with morphological evidence of cell swelling, another method was selected to confirm and extend these findings. METHODS: Primary cultured rabbit esophageal cells were loaded with the fluorescent dye 2'-7'-bis(carboxyethyl)-5,6-carboxyfluorescein so that changes in intracellular pH (pHi) and cell volume could be simultaneously monitored by microfluorimetry. RESULTS: Cells exposed to low pHo in both bicarbonate-free and bicarbonate-containing buffers produced a decline in pHi to as low as 6.5, but this occurred without change in volume. However, when pHo was lowered to < or = 2, pHi declined to <6.5 and volume increased by 25% in 3 minutes. Removal of Na+, K+, or Cl- or adding bumetanide inhibited acid-induced swelling. Also, swelling was inhibited when cells were acidified in Ca2+-free media and eliminated by adding 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid to Ca2+-free media. CONCLUSIONS: Esophageal cells swell when low pHo reduces pHi to <6.5. At pHi <6.5, swelling occurs through excess osmolyte (and consequently water) uptake via a bumetanide-sensitive NaK2Cl cotransporter. Activation of this enzyme at low pHi seems to be mediated by increases in cell Ca2+.

Animals↗
PubMed1997

Effects of luminal hypertonicity on rabbit esophageal epithelium.

The human esophagus is exposed daily to luminal contents that are hypertonic with respect to blood. Because the effects of such exposure are unknown, we investigated the impact of luminal hypertonicity on esophageal epithelial structure and (barrier and transport) function. Rabbit esophageal epithelium was mounted in Ussing chambers and exposed luminally to hypertonic (1,200 mosmol/kgH2O) solutions of mannitol, urea, or NaCl or to normal Ringer solution (300 mosmol/kgH2O). The potential difference (PD), short-circuit current (Isc), and resistance (R) were monitored and, after exposure, tissues were assessed morphologically by light and electron microscopy. Hypertonic mannitol had no significant effect on the electrical or morphological properties of the tissue. However, hypertonic urea and NaCl increased Isc by 91 +/- 31% and 305 +/- 51%, respectively, and decreased R by 20 +/- 6% and 57 +/- 3%, respectively (both P < 0.05 vs. Ringer or mannitol). Furthermore, serosal ouabain blocked the urea-induced increase in Isc completely and the NaCl-induced increase partially (65%) but had no effect on the decline in R. The decline in R for both urea and NaCl was associated with increased [14C]mannitol fluxes and, morphologically, with dilated intercellular spaces but not cell necrosis. These data suggest that hypertonic urea and NaCl, but not hypertonic mannitol, stimulate net Na+ transport in esophageal epithelium and increase permeability via the paracellular route. Notably, the effects of hypertonic urea and NaCl occur rapidly at clinically relevant osmolalities and, though reversible, resolve more slowly. We conclude that hypertonic luminal environments can significantly alter esophageal epithelial structure and function, but that the impact of such exposure depends as much on the nature of the solute as on its osmolality and duration of contact.

Animals↗
PubMed1997

The pathogenesis of gastroesophageal reflux disease: the relationship between epithelial defense, dysmotility, and acid exposure.

Gastroesophageal reflux disease (GERD) is a complex, multifactorial disease for which the initiating factors are unknown. Acid in contact with the esophageal epithelium, however, is a central event in the development of the disease--the disease developing when acid overwhelms the intrinsic esophageal epithelial defenses. Acid breakdown of the tissue defenses is what ultimately leads to symptom production, ulceration, and other complications of GERD. Patients with GERD generally, although not always, have more episodes of reflux than healthy subjects; this is due to more frequent transient lower esophageal sphincter relaxations in the disease group. GERD patients may also have some impairment in peristaltic frequency on swallowing and/or weakness in the strength of peristaltic contractility. Contributions from other components of the acid clearance and tissue-defensive mechanisms are possible but remain to be adequately established as contributing to GERD. It is likely that one reason for the wide clinical spectrum observed with GERD results from differences in types and degrees of defects within the tripartite esophageal defensive system against damage from the phenomenon of gastroesophageal reflux.

Epithelium↗
PubMed1996

Dilated intercellular spaces: a morphological feature of acid reflux--damaged human esophageal epithelium.

BACKGROUND & AIMS: Dilated intercellular spaces are a sign of epithelial damage in acid-perfused rabbit esophagus, a change best identified by transmission electron microscopy. The aim of this study was to determine if this change is also a feature of acid damage to human esophageal epithelium. METHODS: Endoscopic esophageal biopsy specimens from patients with (n = 11) and without (n = 13) recurrent heartburn were examined using transmission electron microscopy. Of 11 patients with heartburn, 6 had erosive esophagitis and 5 had normal-appearing mucosa on endoscopy; 13 controls had no symptoms or signs of esophageal disease. Using a computer, intercellular space diameter was measured from transmission electron microscopy photomicrographs of the specimen from each patient. RESULTS: Intercellular space diameter was significantly greater in specimens from patients with heartburn than those from controls; this was true irrespective of whether the patient had erosive or nonerosive disease. Space diameters of > or = 2.4 microns were present in 8 of 11 patients with heartburn and in no controls. CONCLUSIONS: Dilated intercellular spaces are a feature of reflux damage to human esophageal epithelium. As a morphological marker of increased paracellular permeability, its presence in patients without endoscopic abnormalities may help explain their development of heartburn.

Adult↗
PubMed1996

Why is the high grade inhibition of gastric acid secretion afforded by proton pump inhibitors often required for healing of reflux esophagitis? An epithelial perspective.

The effectiveness of proton pump inhibitors in the treatment of reflux esophagitis is undisputed. The same is true for the mechanism by which their beneficial effects are achieved and, that is, by potent suppression of gastric acid secretion. The underappreciated side of the story is not that potent acid suppression controls the disease but why in fact such potent acid suppression is often required for control of reflux esophagitis when experience dictates that much lesser reductions in gastric acid secretion are effective for control of peptic ulcer disease of stomach and duodenum. The present discussion, which views this issue from the perspective of the epithelium, concludes that specific differences between the nature of gastroduodenal and esophageal epithelial defenses could explain the apparent need for greater suppression of gastric acid secretion to control acid-peptic injury to esophagus as opposed to that of stomach and duodenum. Among the differences cited that may account for the reduced acid-resistance of the esophageal epithelium are: 1) a lack of mucus and bicarbonate secretion by surface epithelial cells, 2) a lack of defensive enhancement by prostaglandin release, 3) a lack of an effective mucus cap after injury, and 4) an apparent lack of capacity to rapidly heal erosions by the process of epithelial restitution.

Antacids↗
PubMed1995

The rationale for continuous maintenance treatment of reflux esophagitis.

Reflux esophagitis is a chronic process associated with frequent episodes of relapse in many patients. In addition, the disease may be progressive in at least some patients. Erosion of the esophageal mucosa precedes the development of some of the complications of the condition. There is accumulating evidence that continuous treatment of patients with erosive esophagitis effectively maintains symptomatic remission and absence of esophageal erosions. Whether such treatment will prevent the development of complications has not yet been demonstrated. We investigated a number of questions concerning the natural history and complications of erosive esophagitis and the need for maintenance treatment for patients with severe manifestations of disease as well as the impact of continuous maintenance treatment on the natural history of reflux esophagitis and its complications.

Chronic Disease↗
PubMed1995

HCl-induced cell edema in rabbit esophageal epithelium: a bumetanide-sensitive process.

BACKGROUND & AIMS: The morphology of acid damage to esophageal epithelium is characterized by marked cell (swelling) edema. This observation suggests that, in the process of acid damage, an increase in osmotic forces develops within the cell that accounts for the increase in cell water. The aim of this study was to document that esophageal cells swell at acidic pH and to explore the nature of the osmolytes and mechanisms responsible for it. METHODS: Cell edema was assessed in sections of rabbit esophageal epithelium by correlating morphological change with change in tissue wet weight after immersion in acidic solutions for up to 4 hours. RESULTS: At pH < or = 2 for 2 hours, tissues gained weight and showed cell edema on both light and electron microscopy. In addition to being time- and pH-dependent, cell edema was dependent on bathing solution osmolytes, specifically Na+, K+, and Cl-, and could be inhibited by tissue pretreatment with bumetanide (or ethacrynic acid). CONCLUSIONS: HCl exposure can spontaneously produce cell edema in esophageal epithelium. The phenomenon is pH- and time-dependent and requires acid stimulation of osmolyte absorption through a bumetanide-sensitive process compatible with an NaK2Cl cotransporter in the epithelial cell membrane.

Animals↗
PubMed1995

Effect of HCl on transmembrane potentials and intracellular pH in rabbit esophageal epithelium.

BACKGROUND/AIMS: Acidification of the basolateral membrane by adding HCl to the serosal solution of esophageal epithelium leads to more necrosis than acidification of the apical membrane by adding HCl to the luminal solution. The aim of this study was to examine the mechanism for this difference. METHODS: The effect of low extracellular pH (pHo) (HCl) on intracellular pH (pHi) and transmembrane potentials was examined in rabbit esophageal cells by impalement with intracellular microelectrodes. RESULTS: Lowering luminal pH to 3.0 had no effect on membrane voltage and/or pHi in either luminally or serosally impaled cells, although a decline in both parameters occurred at pH 1.5 in luminally impaled cells. In contrast, lowering serosal pH from 7.4 to 3.0 progressively reduced membrane voltage and/or pHi. Membrane depolarization at low pHo was inhibited by a high-potassium solution or barium and mimicked by lowering pHi (gassing with CO2) at neutral pHo. CONCLUSIONS: Basolateral, but not apical, membranes of esophageal epithelial cells are highly permeable to H+, accounting for the greater susceptibility to damage from exposure to serosal than luminal acid. Membrane depolarization at low pHo is mediated by low pHi through inhibition of basolateral membrane K+ conductance.

Animals↗
PubMed1995

Reflux esophagitis: overview.

Reflux eosophagitis is one of the most common chronic disorders in humans. While ultimately due to contact of esophageal epithelium with gastric acid and pepsin, the pathogenesis of the condition remains poorly understood. In the present manuscript, some key clinical aspects of this condition are briefly reviewed, including pathogenesis, complications, diagnosis, and treatment.

Esophagitis, Peptic↗
PubMed1994

Effect of adrenergic and cholinergic agents on esophageal bicarbonate secretion in opossums.

The effects of cholinergic and adrenergic agonists and antagonists on esophageal bicarbonate secretion in the opossum were studied in vivo using a recirculated unbuffered saline solution and pH stat technique. The basal rate of secretion was 0.28 +/- 0.02 mumol.h-1.cm-2, and this increased in a dose-dependent manner by intravenous administration of carbachol (maximal increase 0.74 +/- 0.07 mumol.h-1.cm-2 at 6 micrograms/kg). Furthermore, like carbachol, the acetylcholinesterase inhibitor edrophonium also increased bicarbonate secretion, whereas atropine and pirenzepine, which had no effect on basal secretion, abolished the increase in secretion produced by carbachol. Intravenous administration of either adrenergic agonists or antagonists had no significant effect on secretion. These data indicate that basal bicarbonate secretion in the opossum esophagus is independent of intrinsic adrenergic or cholinergic activity, and so not under autonomic nervous system control, but that endogenous release of acetylcholine, presumably from parasympathetic nervous fibers, can stimulate bicarbonate secretion through activation of cholinergic M1 receptors.

Animals↗
PubMed1993

Na(+)-dependent and -independent Cl-/HCO3- exchangers in cultured rabbit esophageal epithelial cells.

BACKGROUND: The mechanisms by which esophageal epithelial cells regulate intracellular pH (pHi) in a physiological solution are unknown. METHODS: Basal-type esophageal cells growing in primary culture were loaded with the fluorescent dye 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein (BCECF) to study pHi by microfluorimetry. RESULTS: The pHi in HEPES buffer was 7.7 +/- 0.03, a value higher than that in CO2/HCO3- buffer, 7.2 +/- 0.1. Cells in HEPES switched to CO2/HCO3- buffer rapidly acidified to pHi of 7, then alkalinized to a new steady-state pHi. The mechanisms for alkalinization in CO2/HCO3- were dependent on two exchangers, one amiloride-sensitive and the other 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS)-sensitive, the latter dependent on Nao and Cli, and so indicative of an Na(+)-dependent Cl-/HCO3- exchanger. Cells in a CO2/HCO3- buffer rapidly alkalinized to pH 8.2 when switched to HEPES, then acidified to a new steady-state pHi. Acidification in HEPES was largely caused by a DIDS-sensitive, Clo-dependent, non-Nao-requiring mechanism, indicative of a cell-acidifying Na-independent Cl-/HCO3- exchanger. CONCLUSIONS: In a physiological buffer, esophageal cells have at least three exchangers for regulation of pHi.

Acids↗
PubMed1993

Mechanisms of HCl-induced lowering of intracellular pH in rabbit esophageal epithelial cells.

BACKGROUND: For acid injury to occur in esophageal epithelium, extracellular HCl must lower intracellular pH. Therefore, we sought to define the mechanisms for translation of low extracellular pH (pHo) into low intracellular pH (pHi). METHODS: To define the mechanisms, primary cultures of rabbit esophageal epithelial cells were loaded with the pH-sensitive fluorescent dye, 2'7''-bis(carboxyethyl)-5(6)-carboxyfluorescein (BCECF), which enabled pHi to be recorded by microfluorimetry. RESULTS: Lowering pHo to 6.0 with HCl caused pHi to decline at 0.07-0.08 units/min and produced an average cellular H+ load of 3-6 mmol/L at 1 minute and of 11 mmol/L at 5 minutes. This degree of acidification was primarily attributable to increased H+ entry via a 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS)-sensitive Clo-dependent mechanism because DIDS or exposure to Clo-free solution blocked cell acidification. Furthermore a contribution to low pHi at low pHo of abolition of acid extrusion via Na+/H+ and Na(+)-dependent Cl-/HCO3- exchangers was sought but not established because exposure at low pHo to either 5-(N-ethyl-N-isopropyl)amiloride (EIPA) or Na(+)-free solution + EIPA increased the degree of acid loading over untreated cells. CONCLUSIONS: Low pHo results in low pHi in esophageal cells primarily because of increased H+ entry via a DIDS-sensitive, Clo-dependent mechanism consistent with the known acid-loading Na(+)-independent Cl-/HCO3- exchanger.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗