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J D Kaunitz

Publications and source records attributed to J D Kaunitz.

At least 37 records · Page 2Linked to original sources
PubMed1997

Human spasmolytic polypeptide decreases proton permeation through gastric mucus in vivo and in vitro.

Exogenously administered trefoil peptides are gastroprotective in rat injury models. We hypothesized that trefoil-associated gastroprotection occurred by decreasing the rate of proton permeation through mucus. Gastric surface cell intracellular pH and mucus gel thickness were measured by in vivo microscopy. Gastric mucosal blood flow was measured by laser-Doppler flowmetry. The effect of human spasmolytic peptide (hSP) on H+ diffusion through 5% purified porcine mucin was measured using an Ussing chamber. Buffering action of mucin was measured by titration. In vivo, gastric mucosal blood flow and mucus gel thickness were not affected by any of the treatments. Topical hSP, but not intravenous hSP, decreased initial acidification rate and elevated the intracellular pH of gastric surface cells during luminal acid challenge. In in vitro studies, hSP dose dependently decreased the diffusion coefficient of H+ through 5% porcine mucin solution. hSP had no significant effect on the buffering action of mucin solutions. These data support our hypothesis that hSP interacts with gastric mucin in a manner that inhibits proton permeation through the mucus gel layer.

Animals↗
PubMed1996

Indomethacin does not alter the effect of pentagastrin on rat gastric defense mechanisms.

We studied the effect of the prostaglandin synthesis inhibitor, indomethacin, on pentagastrin-associated enhancements of gastric mucosal defense mechanisms, using a microfluorometric technique in which mucus gel thickness, intracellular pH (pHi), gastric mucosal blood flow, and acid secretion were measured simultaneously in vivo. Intravenous infusion with pentagastrin (80 micrograms/kg/h) increased mucus gel thickness, induced a hyperemic response to luminal acid, and enhanced pHi homeostasis during acid superfusion. Indomethacin, (5 mg/kg, IP) did not alter the effects of pentagastrin on acid output, mucus gel thickness, mucosal blood flow, and pHi homeostasis. Indomethacin alone did not affect any of these measures. We conclude that the enhancement of gastric defense mechanisms due to pentagastrin is independent of prostaglandin synthesis.

Animals↗
PubMed1996

Gastroprotective effect of ranitidine bismuth citrate is associated with increased mucus bismuth concentration in rats.

BACKGROUND: Antisecretory and bismuth compounds protect the gastric mucosa from injury resulting from non-steroidal anti-inflammatory drugs. AIM: To study the mechanism underlying the gastroprotective effects of ranitidine bismuth citrate (GG311) in rats. METHODS: Indomethacin rat injury model and in vivo microscopy in which acid output, surface cell intracellular pH (pHi), gastric mucus gel thickness, and mucosal blood flow were measured simultaneously. RESULTS: In injury studies, GG311 dose dependently protected against severe injury induced by indomethacin (60 mg/kg subcutaneously). In in vivo microscopic studies, indomethacin significantly decreased mucus gel thickness and increased the initial rate of acidification of gastric surface cells when the superfusate pH was lowered from 7.4 to 1.0, and impaired pHi during acid exposure. Indomethacin had no effect on mucosal blood flow or acid output. GG311 alone had no effect on gel thickness, blood flow, or pHi homeostasis during acid exposure, but improved the initial acidification rate and pHi during superfusion with pH 1.0 solutions in the presence of indomethacin. In separate experiments, indomethacin pretreatment considerably increased gastric mucus bismuth concentrations in rats given GG311. CONCLUSIONS: The gastroprotective effect of GG311 against indomethacin induced gastric injury is associated with high and prolonged gastric mucus bismuth concentrations, which may impair proton permeation across the mucus gel.

Analysis of Variance↗
PubMed1996

Impairment of the gastric hyperemic response to luminal acid in cirrhotic rats.

Liver cirrhosis impairs gastric mucosal resistance to luminal acid in humans and in animal models. Because we have previously shown that pentagastrin enhances defensive as well as aggressive factors implicated in mucosal injury, we examined the hypothesis that the pentagastrin-mediated enhancement of mucosal defense mechanisms may be impaired in cirrhotic rats. Increased acid backdiffusion and susceptibility to gross mucosal injury, associated with an elimination of the hyperemic response to gastric barrier disruption, was observed in cirrhotic rats. In in vivo microscopic studies in anesthetized rats, cirrhosis had no effect on pentagastrin-associated enhancement of mucus gel thickness or baseline gastric mucosal blood flow, although baseline mucus gel thickness was decreased. Cirrhosis did, however, abolish the luminal acid-related hyperemic response to pentagastrin, which was associated with impaired intracellular pH homeostasis during acid superfusion. Cirrhosis did not alter submucosal calcitonin gene-related peptide immunoreactive nerves. We conclude that acid backdiffusion and pentagastrin-associated hyperemic responses are important mucosal defensive factors that are specifically impaired by cirrhosis.

Acids↗
PubMed1996

Regulation of intracellular pH: role in gastric mucosal defence.

The gastric mucosa is constantly exposed to conditions that would normally be damaging to living cells. A complex defensive system has evolved that involves multiple mechanisms arranged in a laminar fashion, that as a whole constitute the gastric mucosal barrier to acid. As antisecretory therapy becomes perfected, more attention has been focused on these defensive components of the gastric mucosal barrier in disease. Recently, our laboratory has developed a means of measuring intracellular pH (pHi), mucosal blood flow, acid secretion, surface cell acidification rate, and acid secretion simultaneously in vivo. This system has enabled our laboratory to explore how the different components of the gastric mucosal barrier interact so as to protect the pHi of the surface cells under a variety of conditions. Analysis of these studies has revealed a significant inverse correlation between the initial fall in pHi of surface cells during luminal acid exposure and the thickness of the mucus gel, suggestive of a role of adherent gastric mucus in retarding the permeation of luminal protons into the epithelial cells. Another correlation has been between recovery of pHi and the presence of a hyperemic response to luminal acid, which suggests that the hyperemic response is an important defense mechanism in the intact mucosa. Our data is consistent with the hypothesis that gastric mucosal defense mechanisms, like gastric acid secretion, are dynamically regulated according to need. Disturbance of the regulation of these mechanisms, for example by cirrhosis, might be one of the major factors underlying clinical ulcer disease.

Acids↗
PubMed1995

Barrier function of the gastric mucus gel.

The gastric epithelium is covered by a continuous layer of secreted mucus and bicarbonate. The function of this mucobicarbonate layer in terms of protecting the epithelial cells from luminal acid is controversial. Several studies conducted in vitro have shown that gastric mucus can slow proton diffusion and can enable the formation of a pH gradient across the mucobicarbonate layer. In our laboratory, simultaneous measurements of intracellular pH and the thickness of the mucus gel overlying gastric surface cells in vivo indicated that surface cell acidification rates and mucus gel thickness were inversely related. This suggests that the gastric mucobicarbonate layer delays proton permeation into gastric surface cells, enabling secreted bicarbonate to neutralize luminal acid. Several theoretical models, including the effects of mucus and bicarbonate secretion, convection, stirring, and lipids are offered as a possible explanation for the experimental observations. Lipid content and additional unstirred layers outside of the mucus gel are offered as possible explanations for the experimental observations. On the basis of the available data and theoretical considerations, we can conclude that all of these factors probably interact in an integrated manner to protect the gastric epithelial cells from damage due to luminal acid.

Animals↗
PubMed1994

Prostaglandin E2 enhances gastric defense mechanisms against acid injury in uremic rats.

BACKGROUND/AIMS: Uremia increases gastric mucosal H+ permeability and acid back-diffusion-related injury in rats. The aim of this study was to examine the effect of the synthetic gastroprotective compound 16,16-dimethyl prostaglandin E2 (16,16-dm PGE2) on the gastric barrier to acid injury in uremic rats. METHODS: Chronic renal failure was induced by subtotal nephrectomy. Acid back-diffusion injury was induced by superfusion with 15% ethanol in 0.15N HCl and was assessed by image analysis. Intracellular pH, initial surface cell acidification rate, and thickness of mucous gel layer were measured with in vivo microscopy. Gastric mucosal blood flow was measured in separate experiments by laser-Doppler flowmetry. RESULTS: Pretreatment with 16,16-dm PGE2 attenuated H+ back-diffusion and prevented the production of gross lesions. 16,16-dm PGE2 increased gastric mucous gel thickness, decreased initial acidification rate, and maintained intracellular pH homeostasis during exposure to luminal acid. Gastric mucosal blood flow was not changed during superfusion with a neutral buffer but increased during acid exposure in rats treated with 16,16-dm PGE2. CONCLUSIONS: 16,16-dm PGE2 attenuated H+ back-diffusion injury in uremic rats. This effect was associated with blunting of the initial decrease of intracellular pH and enhanced surface cell intracellular pH homeostasis during acid exposure. These effects were associated with an increased mucous gel layer thickness and an acid-related increase in blood flow.

16,16-Dimethylprostaglandin E2↗
PubMed1994

Pentagastrin enhances gastric mucosal defenses in vivo: luminal acid-dependent and independent effects.

Stimulation of acid secretion is associated with enhanced resistance of the gastric mucosa to damage by luminal acid. We studied the mechanism by which gastric mucosal defenses are modulated in a system in which mucus gel thickness, intracellular pH (pHi), gastric mucosal blood flow, and acid secretion can be measured simultaneously in vivo, using a recently developed microfluorometric technique. Intravenous infusion of pentagastrin in a dose associated with maximal acid secretion increased mucus gel thickness, pHi, and mucosal blood flow during superfusion with a neutral solution. Subsequent superfusion with an acidic buffer (pH 1.7) further increased blood flow to nearly three times basal. During superfusion with luminal acid, pHi fell more slowly and recovered toward baseline more quickly in pentagastrin-infused rats than in controls. Pretreatment with the H2-receptor antagonist cimetidine abolished the increased blood flow associated with pentagastrin, impairing pHi homeostasis, although cimetidine increased mucus gel thickness in the absence of pentagastrin. We conclude that gastric defense mechanisms at the preendothelial and postepithelial levels are enhanced during acid secretion as part of a histamine-dependent homeostatic mechanism that balances gastric protective mechanisms with acid secretion. The net result of these enhanced defenses is the preservation of gastric surface cell pHi despite the presence of a large proton gradient between lumen and blood.

Animals↗
PubMed1994

Impairment of gastric mucosal defenses measured in vivo in cirrhotic rats.

Patients with cirrhosis have an increased incidence of gastric ulcers and erosions. We evaluated the effect of carbon tetrachloride-induced cirrhosis on rat gastric mucosal defense mechanisms using our recently developed in vivo fluorescence microscopy technique. Cirrhotic rats had increased portal vein pressure, increased serum aminotransferase concentrations and decreased serum albumin concentrations. We noted significantly more spontaneous gross gastric lesions in the cirrhotic rats. In vivo microscopic measurements revealed that cirrhotic rats had (a) a significantly thinner gastric mucous gel layer, (b) a much greater decrease in surface mucosal cell intracellular pH in response to an acid load, (c) decreased gastric mucosal blood flow and (d) decreased surface cell viability. We conclude that spontaneous gastric mucosal lesions in cirrhotic rats may be related to more rapid penetration of acid through a thinner gastric mucous gel layer and a lower mucosal blood flow. These changes are associated with a decreased ability of the surface cells to maintain intracellular pH homeostasis, increased initial gastric surface cell acidification, decreased surface cell viability and a lower blood flow that probably is inadequate to remove the increased acid.

Animals↗
PubMed1993

Inhibition of gentamicin uptake into cultured mouse proximal tubule epithelial cells by L-lysine.

Gentamicin uptake and toxicity was studied in a nontransformed cell line obtained from the S1 segment of the proximal tubule epithelium of a transgenic mouse. Cytotoxicity was assayed using the dye 3-(4,-5dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT). Gentamicin uptake was assayed by a fluorescence polarization assay. No differences in toxicity were found among cells incubated for 4 hours in complete culture medium, enriched Kreb's buffer alone, or enriched Krebs' buffer with added 300 micrograms/mL gentamicin, 0.5 mmol/L L-lysine, or gentamicin plus L-lysine. Uptake of 300 micrograms/mL gentamicin was minimal at zero time and increased as a function of time. Uptake of gentamicin at 4 hours was positively correlated with medium gentamicin concentration. Addition of 0.5 mmol/L L-lysine inhibited uptake of 300 micrograms/mL gentamicin 38.9 +/- 10.2%. No other amino acid, including D-lysine or arginine, significantly changed gentamicin uptake. The authors conclude that gentamicin and L-lysine share a specific uptake mechanism located in the apical membrane of renal proximal tubule cells.

Animals↗
PubMed1993

Isoproterenol enhances rat gastric mucosal barrier function in vivo.

BACKGROUND: The mechanism by which topical isoproterenol protects the gastric mucosa from ethanol-induced injury is unclear; previous studies suggest that enhancement of mucosal blood flow may be contributory. Therefore, we investigated the role of isoproterenol pretreatment on rat gastric mucous gel layer thickness, mucosal blood flow, and surface cell intracellular pH. METHODS: A portion of the gastric corpus of an anesthetized rat was isolated in a superfused chamber. Intracellular pH was measured with the fluorescent dye 5(6)-carboxyfluorescein diacetate, mucous gel thickness was measured by quantifying the distance between the focal planes of the epithelial cell and the gel surfaces, and mucosal blood flow was measured in separate experiments with a laser-Doppler flowmeter. RESULTS: Pretreatment with topical isoproterenol markedly increased gastric mucous gel layer thickness, decreased surface cell initial acidification rates, and significantly enhanced the recovery of intracellular pH toward baseline values. Gastric mucosal blood flow was significantly higher in the isoproterenol-treated group compared with untreated controls, initially increasing, decreasing, and then increasing a second time during superfusion with acidic solutions. CONCLUSIONS: Isoproterenol preserves gastric surface cell intracellular pH during acid superfusion. This effect may be a result of an increased thickness of the mucous layer, which delays proton entry into the surface cell, and an increase in mucosal blood flow in response to luminal acid, which appears to enhance recovery from intracellular acidosis.

Acids↗
PubMed1993

Effect of orogastric nicotine on rat gastric mucosal gel thickness, surface cell viability and intracellular pH.

Intracellular pH was measured in vivo using a fluorescent, microscopic technique in gastric surface cells of rats exposed to orogastric nicotine on an acute or chronic basis. Mucosae were superfused with solutions of pH 3 or pH 1.7 in order to examine the rate of intracellular acidification and recovery. In rats acutely exposed to nicotine, the response of intracellular pH to superfusion with acidic solutions was blunted with respect to control rats in a dose-dependent manner. In contrast, intracellular pH of rats chronically treated with nicotine had an exaggerated response with respect to control rats, with more rapid acidification and diminished ability to maintain intracellular pH in the physiologic range. Mucus gel thickness was increased after acute nicotine exposure in a dose-dependent manner, whereas a dose-dependent decrease in thickness was seen after chronic nicotine exposure. Cell viability using the fluorescent vital dye propidium iodide was increased in rats acutely treated with orogastric nicotine; conversely, viability was decreased in chronically treated rats. We conclude that acute nicotine exposure diminishes, whereas chronic nicotine exposure enhances, the effect of luminal acidity on mucosal surface cell intracellular pH and cell viability. These divergent effects correlate inversely with mucus gel thickness, suggesting that the mucus gel layer is an important component of the gastric mucosal barrier.

Administration, Oral↗
PubMed1992

Na+/H+ exchange regulates intracellular pH of rat gastric surface cells in vivo.

Intracellular pH (pHi) and viability of gastric surface cells of the rat stomach in response to luminal acidification, and the role of Na+/H+ exchange in maintaining pHi homeostasis were studied in vivo using a fluorescent microscopic technique. pHi was measured during superfusion with buffers of pH 1.2-7.4. When the pH of the superfusate was 7.4, baseline pHi was unchanged. Superfusion with pH 3 buffer rapidly decreased pHi to 6.7, with subsequent recovery to baseline pHi within 15 min despite continuing acid exposure. Superfusion with buffers of pH 1.7 and 1.2 decreased pHi continuously to below 6.2 with no recovery observed. Despite the relentless decline in pHi during superfusion with pH-1.2 and -1.7 solutions, over 75% of the surface cells were still viable, as measured by exclusion of the vital dye propidium iodide. We then examined the role of Na+/H+ exchange in the regulation of pHi. Superfusion with amiloride did not affect recovery of pHi from intracellular acidification induced by a NH4Cl prepulse. Exposure to the potent, lipophilic Na+/H+ exchange inhibitor 5-(N,N-hexamethylene)-amiloride (HMA), either in the superfusate or by close arterial perfusion, decreased baseline pHi from 7.1 to 6.8. Close arterial perfusion of HMA additionally attenuated the recovery of pHi to baseline during superfusion with pH 3 buffer. We conclude that luminal protons permeate into the cytoplasm of gastric surface cells, where they are eliminated by an Na+/H+ exchanger, most probably localized to the basolateral membrane.

Amiloride↗
PubMed1991

In vivo measurement of rat gastric surface cell intracellular pH.

Intracellular pH (pHi) of the surface mucous cells of the rat stomach was measured in vivo using a fluorescent microscopic technique. Gastric surface mucous cells were loaded with fluorescein by superfusion with 5(6)-carboxy-fluorescein diacetate, and the ratio of the intensity of emitted fluorescence at 495 and 450 nm excitation was determined by image analysis of videotapes. An in vivo calibration curve was constructed using 10(-5) M nigericin to equilibrate pHi and extracellular pH, and intra- and extracellular potassium concentrations. The pHi of the gastric surface cells was 7.22 +/- 0.06, and pHi was stable over 45 min. A pulse of 20 mM NH4Cl in Krebs solution rapidly alkalinized the cells to pH 7.7, followed by a slow return of pHi to baseline pH 7.2. After withdrawal of NH4Cl, pHi dropped to 6.7 with gradual recovery to baseline. pHi increased when the mucosa was superfused, in the presence of nigericin, with 150 mM KCl solutions and decreased when superfused with 2.6 mM KCl solutions. Perfusing with pH 3 Krebs buffers transiently decreased pHi, whereas superfusion with pH 1.2 Krebs irreversibly decreased pHi. These findings confirm that the measured fluorescence was intracellular and that the cells responded to changes in luminal pH.

Ammonium Chloride↗
PubMed1989

Ca2+ and cAMP activate K+ channels in the basolateral membrane of crypt cells isolated from rabbit distal colon.

Using patch-clamp techniques, we have studied Ca2+-activated K+ channels in the basolateral membrane of freshly isolated epithelial cells from rabbit distal colon. Epithelial cell clusters were obtained from distal colon by gentle mechanical disruption of isolated crypts. Gigaohm seals were obtained on the basolateral surface of the cell clusters. At the resting potential (approximately -45 mV), with NaCl Ringer's bathing the cell, the predominant channels had a conductance of 131 +/- 25 pS. Channel activity depended on voltage as depolarization of the membrane increased the open probability. In excised inside-out patches, channels were found to be selective for K+ over Na+. Channel activity correlated directly with bath Ca2+ concentration in the excised patches. Channel currents were blocked by 5 mM TEA+ and 1 mM Ba2+. In cell-attached patches, after addition of the Ca2+ ionophore A23187, which increases intracellular Ca2+, open probability was markedly increased. Channel activity was also regulated by cAMP as addition of 1 mM dibutyryl-cAMP in the bath solution in cell-attached patches increased channel open probability over 20-fold. Channels that had been activated by cAMP were further activated by Ca2+. We conclude that the basolateral membrane of epithelial cells from descending colon contains a class of potassium channels, which are regulated by intracellular Ca2+ and cAMP.

Animals↗
PubMed1988

Preparation and characterization of viable epithelial cells from rabbit distal colon.

A preparation of viable epithelial cells, suitable for transport studies, was prepared from rabbit distal colon. Enzymatic digestion of scraped mucosa liberated a population of intact colonic glands that were dissociated into cells by gentle agitation in culture medium. Metabolism of [14C]glucose was constant over 2 h and was inhibited 70% by 1 mM ouabain. Cells were loaded with the trapped, pH-sensitive fluorescent dye 2'-7'-bis(carboxyethyl)-5(6)-carboxyfluorescein acetoxy methyl ester and leaked 0.1% of the dye per minute. Cell pH was 7.21 +/- 0.03 (SE) (n = 15) in pH 7.4 Ringer medium. Intracellular potassium concentration, as measured by a nigericin null-point technique, was 128 +/- 8 mM. Plasma membrane potential measured with the potential-sensitive fluorescent dye 3,3-dipropylthiadicarbocyanine iodide was -52 +/- 2 mV. Recovery of intracellular pH in acid-loaded cells occurred after exposure to sodium-containing medium and was inhibited by 5 x 10(-4) M amiloride. It is concluded that viable epithelial cells can be prepared from rabbit distal colon with relative simplicity and in high yield. These cells are suitable for measurement of intracellular pH and membrane potential and are thus a convenient model system for study of colonic cell physiology.

Animals↗