Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “SEROSITIS”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 757 records · Page 42Linked to original sources
PubMed2004

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.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed2002

EGF promotes gastric mucosal restitution by activating Na(+)/H(+) exchange of epithelial cells.

This study was conducted to determine whether the contributions of epidermal growth factor (EGF) to gastric mucosal restitution after injury are mediated by stimulation of Na(+)/H(+) exchangers in surface mucous cells (SMC). Intact sheets of guinea pig gastric mucosae were incubated in vitro. Intracellular pH (pH(i)) in SMC was measured fluorometrically, using 2',7'- bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein. Restitution after Triton X-100-induced injury was evaluated by recovery of electrical resistance. At neutral luminal pH, exogenous EGF (ex-EGF) increased pH(i) and enhanced restitution in the absence but not in the presence of serosal HCO. During exposure to luminal acid, ex-EGF not only prevented intracellular acidosis but also promoted restitution. These effects of ex-EGF were blocked by serosal amiloride or anti-EGF-receptor antibody. In the absence of ex-EGF, restitution was inhibited by replacement of luminal and serosal solutions with fresh solutions and was blocked more completely by serosal anti-EGF-receptor antibody. These results suggest that both endogenous and ex-EGF contribute to restitution via basolateral EGF receptors, with effects mediated, at least in part, by stimulation of basolateral Na(+)/H(+) exchangers.

Amiloride↗
PubMed1980

Na+-dependent H+ and Cl- transport in in vitro frog gastric mucosa.

Na+ dependency of H+ and Cl- transport in resting and stimulated gastric mucosae was investigated. We measured transepithelial potential difference (PD), short-circuit current (Isc), conductance, H+ secretion (JH), and unidirectional fluxes of 36Cl- (muscosal (m) to serosal (s), JClm leads to s and JCLs leads to m) during Isc conditions in Ussing-type chambers. Resting tissues: Na+-free serosal solution (choline replacement), but not mucosal, Ringer solution caused PD and Isc to decrease to zero with a time course identical to that observed with Cl--free solutions. Conductance also decreased by more than 50%. Isc = JCLs leads to m--JCLm leads to 8 = JClnet during control ([Na+] = 105 mM), and Na+-free conditions. When [Na+] = 50 mM (choline replacement) Isc (=JClnet) was reduced by approximately 25%; when K+ replaced Na+, Isc (=JClnet) was reduced by approximately 65%. The dependence of Isc on [Na+] (choline replacement) was sigmoidal indicating that there may be two sites at which Na+ activates Cl- secretion. Plots of 1/Isc vs. 1/[Cl-] with different [NA+] indicated, that the affinity of the Cl- "carrier" may be affected by [Na+]. stimulated tissues: Na+-free (choline replacement) solutions caused PD, Isc, and JClnet all to decrease to zero but sometimes Na+-containing mucosal solution caused JH to increase back to 50% of control, whereas Isc increased by only 16%. Na+-free effects were not reversed by 1 mM dibutyryl cAMP plus 0.1 mM isobutyl methylxanthine in the serosal solution. As [Na+] was increased, Isc (sigmoidal) and JH (monotonic) both increased. K+ replacement of Na+ caused a larger decrease in Isc than when choline was used; JH remained constant if [Na+] greater than or equal to mM. We have proposed that the energy-dependent step for active Cl- transport occurs at the serosal membrane in a Na+-coupled process. Cl- that accompanies JH during open-circuit conditions may utilize a separate system.

Animals↗
PubMed1984

Ion transport by rabbit descending colon: mechanisms of transepithelial potassium transport.

In vitro preparations of rabbit descending colon were studied under steady-state short-circuit conditions to determine 1) the K concentration dependence of unidirectional K fluxes; 2) the effects of the K channel blocker barium and the diuretic agent furosemide; and 3) the steady-state tissue specific activity of 42K when added to the luminal bathing solution. Results from these studies reveal that 1) labeling of cellular K from the mucosal solution is less than 25% of that from the serosal solution; 2) both unidirectional K fluxes are composed of saturable and nonsaturable components; 3) the serosal-to-mucosal saturable component is abolished by ouabain, and subsequent addition of 2,4-dinitrophenol abolishes the saturable component of the mucosal-to-serosal K flux; 4) luminal or serosal barium alters K transport in a manner consistent with the presence of barium-sensitive K conductances at both membranes; 5) luminal furosemide did not alter K transport; and 6) there is no shunt selectivity for K. We conclude that the majority of both unidirectional K fluxes follow a transcellular pathway and that both the apical and basolateral membranes possess active K uptake mechanisms and barium-sensitive K exit mechanisms.

2,4-Dinitrophenol↗
PubMed1984

Association between HCO3(-) absorption and K+ uptake by Amphiuma jejunum: relations among HCO3(-) absorption, luminal K+, and intracellular K+ activity.

Titration techniques and K+- sensitive microelectrodes have been used to investigate the relations among HCO3(-) absorption, luminal K+, and intracellular K+ activity in in vitro Amphiuma jejunum. The HCO3(-) absorptive flux (JHCO3(-] measured by pH-stat under short circuit was reduced by removal of K+ from the medium but not by replacement of Na+ with choline. JHCO3(-) exhibited a seasonal variation when K+ was absent from the media and was increased to a maximum when K+ equaled 5 mM. Addition of K+ to a K+-free luminal medium stimulated JHCO3(-) much more than addition to the serosal medium. Acetazolamide (10(-4) M) blocked K+-stimulated HCO3(-) absorption while benzolamide reduced the short-circuit current associated with HCO3(-) absorption much more rapidly when added to the mucosal bathing medium. Intracellular K+ activity (aik) and mucosal membrane potential (psi m) of jejunal villus cells were measured with double-barreled microelectrodes. When bathed bilaterally with HCO3(-)-containing media, K+ was actively accumulated for many hours (aik = 58.5 mM) but in the presence of ouabain fell to equilibrium (16 mM) after 2 h. In contrast, when HCO3(-) absorption was induced by removal of serosal HCO3(-), aik was elevated to 83.6 mM and, after 4-h exposure to ouabain cell K+, remained far above electrochemical equilibrium at 33 mM. Tissues bathed in Na+-free (Tris) media containing ouabain retained cell K+ after 4 h at even higher levels (46 mM). Cell K+ activity was reduced by removal of K+ from either the mucosal or serosal medium. Acetazolamide reduced aik over 2 h in Na+-free media from 66 to 42 mM. The decline in aik was associated with a concomitant decline in the HCO3(-) absorptive current. It is concluded that K+ is actively accumulated across both luminal and serosal membranes of the jejunal absorptive cell and that the luminal uptake mechanism is linked to HCO3(-) absorption or an equivalent process.

Absorption↗
PubMed1984

Active transport of lead-210 by everted segments of rat duodenum.

Everted gut sacs prepared from rat duodenum can transfer 210Pb from mucosal to serosal surfaces against concentration gradients in vitro. The mechanism requires oxygen and is significantly inhibited by sodium azide, sodium iodoacetate, 2,4-dinitrophenol, sodium cyanide, and sodium fluoride. Lack of oxygen or the presence of metabolic inhibitors produced greater relative inhibition of net serosal transfer but greater absolute decrements of net mucosal uptake. Treatment of rats prior to sac preparation with either intravenous FeCl2 or endotoxin, or the addition of FeCl2 to the mucosal medium, selectively inhibited net serosal transfer. Net mucosal uptake and net serosal transfer were significantly negatively correlated with animal weight. Jejunal or ileal sacs did not actively transport 210Pb.

2,4-Dinitrophenol↗
PubMed1985

Sodium dependence of luminal alkalinization by rabbit ileal mucosa.

Stripped rabbit ileal mucosa was studied in vitro in Ussing chambers under short-circuit conditions using the pH-stat technique to determine basal rates of luminal alkalinization; the contribution of the shunt pathway to the alkalinization process; the effects of Na, Cl, or HCO3 removal from the bathing solutions on luminal alkalinization; and the effects of epinephrine, ouabain, 4,4'-diisothiocyanostilbene-2,2'-disulfonate (DIDS), acetazolamide, prostaglandin E1 (PGE1), A23187, sugars, or amino acids on the alkalinization process. Results from these studies reveal that, under basal conditions, the rate of luminal alkalinization accounts for 81% of the basal short-circuit current (Isc), although there was no correlation between the rate of alkalinization and Isc. The contribution of the shunt to the alkalinization process accounts for less than 10% of the mucosal-to-serosal HCO3 flux. Removal of Cl from the bathing solutions increased the rate of luminal alkalinization and decreased Isc. Sodium removal from the bathing solutions reduced both Isc and the rate of luminal alkalinization. Addition of DIDS to the luminal or serosal bathing solution reduced luminal alkalinization less than 30%. Acetazolamide, PGE1, and A23187 were all without effect on luminal alkalinization. Addition of 3-O-methyl-D-glucose or L-alanine to the luminal bathing solution did not alter luminal alkalinization but increased Isc, D-Glucose added to the luminal bathing solution reduced luminal alkalinization. This effect appears to result from metabolic acid production since 1) it is not seen with L-alanine or 3-O-methyl-D-glucose; 2) in the absence of HCO3 in the bathing solutions, D-glucose increased luminal acidification; and 3) luminal addition of fructose also reduced the rate of luminal alkalinization. Addition of epinephrine to the serosal bathing solution stimulates a Na-dependent serosal alkalinization process. These results suggest that luminal alkalinization results from Na-dependent, transcellular HCO3 transport and that a Na-dependent, HCO3 absorptive process is stimulated by adrenergic agents.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1986

Adrenergic agents stimulate and cholinergic agents inhibit H+ secretion by amphibian jejunum.

In vitro segments of Amphiuma jejunum secrete H+ spontaneously. This study explored the effect of cholinergic and adrenergic agents on H+ secretion. Segments of mucosa were short-circuited and exposed on their mucosal surface to HCO3- -buffered medium while the pH of the unbuffered serosal medium was held by the pH-stat technique. Methacholine added to the serosal medium nearly abolished the spontaneous short-circuit current (Isc) and serosal alkalinization (JHCO3-) with an EC50 of 3.7 X 10(-7) M. Subsequent addition of norepinephrine (NE) to the serosal medium caused a dose-dependent increase in Isc and JHCO3. For three catecholamines the order of potency was epinephrine greater than NE greater than isoproterenol. The spontaneous Isc was significantly reduced (P less than 0.05) by the gastric H+-K+-ATPase inhibitor omeprazole, while the NE-induced Isc was unaltered by the inhibitor. Replacement of medium Na+ with choline abolished the response to NE. The NE-induced Isc was also reduced by methacholine. Acetazolamide inhibited the spontaneous and NE-induced Isc and JHCO3. In summary, cholinergic and adrenergic agents have opposing effects on intestinal H+-HCO3- transport. Jejunal acid secretion may be controlled in part by these antagonistic influences. Adrenergically activated acid secretion occurs by a different mechanism than spontaneous acid secretion.

Acetazolamide↗
PubMed1986

Effects of phorbol esters on sodium and chloride transport in rat colon.

To determine the role of protein kinase C in the regulation of active electrolyte transport in rat descending colon, the effects of phorbol dibutyrate (PDB) were studied using the Ussing chamber/voltage-clamp technique. PDB added to the serosal surface increased the short-circuit current in a concentration dependent manner with a EC50 of 3 X 10(-8) M and a maximal effect at 10(-7) M PDB. The effect was not seen with the inactive alpha-phorbol analogue but was reproduced with 1-oleoyl-2-acetylglycerol, a more permeable analogue of diacylglycerol. PDB caused a decrease in mucosal-to-serosal and net fluxes of Na and Cl and an increase in serosal-to-mucosal Cl flux, indicating inhibition of Na and Cl absorption and stimulation of Cl secretion. The PDB-induced increase in Cl secretion was virtually abolished by both indomethacin and ibuprofen, indicating a dependence on arachidonic acid metabolism via the cyclooxygenase pathway. The Cl secretion was inhibited by verapamil and Ca2+-free bathing solution on the serosal surface but not by dantrolene, suggesting the importance of extracellular Ca2+ but not intracellular stored Ca2+ in the PDB-induced secretion. The Cl secretory effect was also inhibited by tetrodotoxin and atropine, suggesting involvement of cholinergic nerves. In contrast, the PDB-induced decrease in Na and Cl absorption was not dependent on metabolites of the cyclooxygenase pathway, not dependent on extracellular Ca2+, and not blocked by tetrodotoxin. It appears likely that protein kinase C is involved in the regulation of rat colonic active Na and Cl absorption and electrogenic Cl secretion but that the pathways involved are different in the two transport systems.

Animals↗
PubMed1987

Acid secretion in isolated guinea pig colon.

Isolated guinea pig distal colons secreted acid into the mucosal bathing solution at a rate of 1.0-1.5 mumol X cm-2 X h-1 when the preparations were mounted in Ussing chambers and bathed with HCO3(-)-CO2-free solution. The rates of the acidification and alkalinization of the solutions were measured by a pH stat system or calculated from changes in the pH of the solution. The acid secretion was localized in the middle and distal parts of the colon but absent in the proximal part of the colon and the cecum. The mucosal acidification was accompanied by serosal alkalinization, the rate of the latter being approximately 60% of the former. A carbonic anhydrase inhibitor, methazolamide (10(-4) M), reduced both the mucosal acidification and serosal alkalinization rates by a similar magnitude. The mucosal acidification was completely abolished by mucosal K+-free conditions but unaffected by mucosal Na+-free conditions. Ouabain added to the mucosal solution promptly inhibited the acid secretion. Dose dependency of the inhibition conformed to the Michaelis-Menten equation with a half-maximal effect at 4 X 10(-6) M. When the pH of the mucosal solution was reduced to 4.3, the rate of the mucosal acidification remained essentially the same as that at pH = 7.4. Vanadate (10(-4) M) added to both the mucosal and serosal solutions significantly reduced the mucosal acidification rate. These results suggest that CO2 derived from the epithelial metabolism is hydrated by carbonic anhydrase in the cell and released H+ enters the mucosal solution while HCO3- enters the serosal solution. H+ exit across the mucosal membrane may be mediated by H+-ATPase that is sensitive to ouabain.

Acids↗
PubMed1989

Regulation of bicarbonate transport in rabbit ileum: pH stat studies.

Although it is well recognized that the ileum secretes bicarbonate, understanding of the mechanisms of the transport of this ion has been limited by the inability to measure fluxes in vitro. However, by clamping the bathing fluid at a set pH using a pH stat system, accurate measurements of bicarbonate movement can be made. Bicarbonate transport in rabbit ileum in vitro was measured by simultaneously employing both the pH stat and short-circuit techniques. The role of acid-base balance was assessed by systematically altering buffer bicarbonate concentration, pH, and partial pressure of CO2 (PCO2). Bicarbonate secretion was strongly correlated with both serosal [HCO3-] (r = 0.824, P less than 0.01) and serosal pH (r = 0.793, P less than 0.01). Bicarbonate absorption was not significantly altered by mucosal [HCO3-], pH, or PCO2. Paracellular movement of bicarbonate, as assessed by voltage clamping and diffusion potential experiments, did not appear to be a major component of transcellular transport. Epinephrine stimulated bicarbonate absorption significantly, both in Cl-containing and Cl-free Ringer solution but did not alter bicarbonate secretion. Epinephrine-induced decreases in short-circuit current were correlated with enhanced bicarbonate absorption. Bicarbonate secretion was inhibited by serosal chloride and serosal bumetanide; mucosal chloride stimulated bicarbonate secretion. Mucosal chloride did not affect bicarbonate absorption. Glucocorticoids enhanced both bicarbonate absorption and secretion. These results suggest that there are discrete apical and basolateral transport mechanisms that regulate bicarbonate transport. Bicarbonate secretion may be mediated by a basolateral bumetanide-sensitive, chloride-inhibitable transporter and by an apical chloride-bicarbonate exchange process.

Animals↗
PubMed1990

NaCl transport across equine proximal colon and the effect of endogenous prostanoids.

In contrast to in vivo findings, the equine proximal colon fails to demonstrate significant net absorption of Na+ and Cl- under in vitro conditions. The present study was undertaken to determine if endogenous prostanoids are responsible for this apparent lack of ion transport. Proximal colonic tissues from ponies were preincubated in either normal Ringer solution or in Ringer containing 1 microM indomethacin and studied in Ussing chambers containing these solutions. Untreated colonic mucosa demonstrated negligible Na(+)-Cl- absorption in the basal state. In contrast, indomethacin-treated colon significantly absorbed Na+ and Cl-, primarily as the result of an equivalent increase in the mucosal-to-serosal flux of these ions. Preincubation of proximal colon in 0.1 mM ibuprofen-treated Ringer yielded similar results. Treatment of indomethacin colon with 1 mM mucosal amiloride eliminated net Na(+)-Cl- absorption without affecting the short-circuit current (Isc). The Isc in control tissue was significantly greater than in indomethacin-treated tissue and was reduced by 0.1 mM serosal furosemide. Serosal addition of 0.1 microM prostaglandin E2 or 10 mM serosal plus mucosal theophylline to indomethacin-treated tissues abolished net Na(+)-Cl- absorption and increased the Isc to levels indistinguishable from control. In contrast, control tissues were essentially unaffected by these secretagogues. These findings indicated that Na(+)-Cl- absorption in equine proximal colon was electroneutral (possibly involving Na(+)-H+ exchange) and that the tissue was capable of electrogenic Cl- secretion. However, under the in vitro conditions, basal ion transport was dominated by endogenous prostanoids that abolished Na(+)-Cl- absorption and elicited near-maximal electrogenic Cl- secretion.

Aldosterone↗
PubMed1991

Use of a modified Ussing chamber to monitor intestinal epithelial and smooth muscle functions.

A technique that allows the simultaneous monitoring of epithelial and smooth muscle function was developed and used to study rat small intestine in vitro. A Ussing chamber was modified so that a strain gauge force transducer could be sewn to the serosal surface of an intestinal segment clamped in the chamber. The apparatus was used to monitor short-circuit current, potential difference, and resistance across the segment, and contractions of the longitudinal layer of the muscularis externa. Both spontaneous activity and responses to the application of carbachol were recorded. Carbachol applied to the serosal side induced dose-dependent increases in both short-circuit current and contractile force. The median effective doses of the two responses differed, with contractions being more sensitive to the drug. Carbachol applied to the mucosal side induced no changes in either epithelial or contractile activities. The ability of the serosal strain gauge transducer to monitor contractions faithfully was tested in an organ bath in which the gut segment was attached to an external force-displacement transducer. There was a close correlation between the dose-dependent increase in force in response to carbachol measured by the serosal transducer and that measured by the force-displacement transducer (r = 0.988). Thus our technique can be used to study simultaneously epithelial and smooth muscle functions of the intestine.

Animals↗
PubMed1993

Stimulation of Cl- and HCO3- secretion by intramural cholinergic neurons in guinea pig antrum in vitro.

Regulation of Cl- and HCO3- secretion by intramural cholinergic neurons was investigated in guinea pig antrum in vitro. Sheet preparations composed of the mucosa and the submucosa were mounted between Ussing chambers and bathed with buffer-free solution on the luminal surface and with HCO3(-)-CO2 solution on the serosal side. Short-circuit current (Isc), unidirectional fluxes of 36Cl and 22Na, and the luminal alkalinization rate (JOHSL) were determined. Electrical stimulation of the preparations elicited increases in both JOHSL and Isc, which were inhibited by tetrodotoxin (TTX) and atropine. Physostigmine also evoked TTX- and atropine-sensitive increases in JOHSL and Isc. Similar increases in JOHSL and Isc were observed when the muscarinic agonist bethanechol chloride (BCh) was added to the serosal side. The responses to BCh were not affected by TTX. The BCh-induced increase in JOHSL was largely abolished by removal of HCO3- or Na+ and addition of ouabain (serosal side) but was neither sensitive to Cl- removal nor associated with 22Na secretion. The increase in Isc induced by BCh was associated with the increase in 36Cl secretion and was inhibited by removal of Cl- or Na+ and by addition of bumetanide or ouabain (both, serosal side). These results suggest that the submucosal cholinergic neurons are involved via muscarinic receptors in the stimulation of epithelial HCO3- and Cl- secretion. For both HCO3- and Cl-, the cellular and membrane mechanisms of secretion induced by muscarinic stimulation, although not entirely clear, appear to be different from those occurring under baseline conditions.

Animals↗
PubMed1994

Vasomotion induces regular major oscillations in jejunal mucosal tissue oxygenation.

The mucosa of the small intestine has some unique microcirculatory features that may result in significant tissue oxygenation changes even under physiological conditions. To prove this hypothesis we investigated mucosal and serosal oxygenation in an autoperfused, innervated jejunal segment in pigs. Eight animals (30-40 kg) were anesthetized, paralyzed, and normoventilated. A small segment of the jejunal mucosa and serosa was exposed by a midline laparotomy and an antimesenteric incision. Mucosal and serosal oxygen tensions were measured using Clark-type surface oxygen electrodes. Mucosal hemoglobin saturation and concentration were determined by tissue reflectance spectrophotometry. Systemic hemodynamics, mesenteric-venous acid base, and blood gas variables, as well as systemic acid-base and blood gas variables and jejunal electromyogenic potentials, were recorded. Measurements were performed after a rest period at 0, 30, 60, and 90 min. All animals remained hemodynamically stable. At time 0 the jejunal oxygen extraction ratio was 0.33 +/- 0.05, the mean serosal PO2 was 60.25 +/- 7.69, the mean mucosal PO2 was 25.47 +/- 4.41 mmHg, and the mean mucosal hemoglobin saturation was 46.36 +/- 6.22%. Mean values did not change with time. In contrast to serosal PO2, mucosal PO2, mucosal hemoglobin oxygen saturation, and hemoglobin concentration showed rhythmic oscillations with a frequency of 3.4-5 cycles/min that were unrelated to systemic hemodynamic parameters, respiratory frequency, and intestinal peristalsis. From this we concluded that the jejunal mucosa demonstrates significant, regular changes in oxygenation parameters that are locally mediated. We speculate that the physiological basis for this phenomenon is the countercurrent arrangement of microvessels in conjunction with vasomotion.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Interstitial buffer capacity influences Na+/H+ exchange kinetics and oxyntic cell pHi in intact frog gastric mucosa.

We studied the influence of interstitial buffer capacity and CO2-HCO3- on oxyntic cell intracellular pH (pHi) in intact frog gastric mucosa. Oxyntic cells in stripped gastric mucosa of Rana esculenta were loaded with the pH-sensitive dye 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein, and pHi was assessed fluorometrically. In the presence of a constant serosal and luminal pH, oxyntic cell pHi was dependent on the serosal but not the luminal concentration of cell-impermeable buffer ions such as N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES), tris(hydroxymethyl)aminomethane, N-tris(hydroxymethyl)methyl-2-aminoethanesulfonic acid, and 3-(N-morpholino)propanesulfonic acid. The stepwise increase in oxyntic cell pHi from 6.74 +/- 0.05 with 1 mM HEPES to 7.23 +/- 0.08 was almost completely inhibited by removal of serosal Na+ and by amiloride and dimethyl amiloride, suggesting that it was largely due to Na+/H+ exchange. Increasing the serosal concentration of a CO2-HCO3- buffer from 1% CO2-4 mM HCO3- to 10% CO2-40 mM HCO3- increased oxyntic cell pHi from 7.03 +/- 0.06 to 7.39 +/- 0.07. This CO2-HCO(3-)-dependent pHi increase was also Na+ and amiloride sensitive, but high HCO3- concentrations increased pHi even in the absence of Na+, K+, or Cl-, and in the presence of omeprazole, bafilomycin A1, or acetazolamide. We suggest that in intact frog gastric mucosa, cellular proton extrusion acidifies the interstitial pH immediately adjacent to the basolateral membrane of the oxyntic cells in the absence of a high interstitial buffer capacity.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1996

Tumor necrosis factor-alpha induces Cl- and K+ secretion in human distal colon driven by prostaglandin E2.

Increased levels of tumor necrosis factor-alpha (TNF-alpha) have been found in, for example, inflammatory bowel disease (IBD) and human immunodeficiency virus (HIV) infection. To investigate a possible contribution of TNF-alpha to the pathogenesis of diarrhea in these diseases, ion transport of human distal colon was studied in the Ussing chamber in vitro. Serosal addition of TNF-alpha increased short-circuit current (Isc) of partially stripped tissues in a dose-dependent manner. Maximum Isc increase of 1.8 +/- 0.2 mumol.h-1.cm-2 was reached after 60 +/- 9 min at 200 ng/ml TNF-alpha. Bidirectional tracer flux measurements revealed that TNF-alpha induced an increase in 36 Cl serosal-to-mucosal flux, a decrease in 36Cl- mucosal-to-serosal flux, and a slight increase in K+ secretion indicated by an increased secretory 86Rb net flux. In the highly differentiated colonic epithelial cell line HT-29/B6, TNF-alpha had no effect on Isc, suggesting a mediation step located in the subepithelium. This supposition was supported by measurements on totally stripped human tissues, since removal of subepithelial layers by total stripping reduced the TNF-alpha effect by 40%. Experiments with tetrodotoxin (10(-6)M) indicated that the TNF-alpha effect was not mediated by the enteric nervous system. The specific 5-lipoxygenase blocker ICI-230487 (5 x 10(-8)M) also had no effect on TNF-alpha action. In contrast, inhibition of cyclooxygenase by indomethacin (10(-6)M inhibited the effect of TNF-alpha. Radioimmunoassay of prostaglandin E2 (PGE2) in the serosal bathing solution revealed an increase in PGE2 production/release after addition of TNF-alpha, which paralleled the Isc response. We conclude that TNF-alpha changed Cl- and K+ transport toward secretion in human colon. This effect was mediated by PGE2 produced by subepithelial cells. Thus TNF-alpha could be a mediator of diarrhea during intestinal inflammation, e.g., in IBD and HIV infection.

Biological Transport↗
PubMed1996

Evidence for Cl(-)-independent HCO3- transport in basolateral membranes of Necturus oxyntopeptic cells.

Luminal H+ secretion by gastric mucosa is accompanied by basolateral HCO3- release. A basolateral Cl-/HCO3- exchanger is known to mediate HCO3- extrusion from oxyntopeptic cells during resting and secretagogue-induced apical HCl secretion. From recent work, we hypothesized that there might be a Cl(-)-independent pathway for basolateral HCO3- exit in Necturus oxyntopeptic cells. In this study, we used a fluorescent pH indicator [2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein] to evaluate Cl(-)-independent HCO3- transport across the basolateral membranes of intact oxyntopeptic cells. Removal of serosal Cl- increased intracellular pH (pHi) (7.05 to 7.25), consistent with Cl(-)-dependent HCO3- extrusion. Removal of serosal Na+ in the absence of Cl- resulted in significant acidification of pHi (7.10 to 6.89), but studies involving amiloride, 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), and 0 HCO3(-)-N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid-buffered solutions suggest that Na(+)-dependent changes in pHi are due to Na+/H+ exchange. Our studies demonstrate a marked concentration-dependent alkalinization when tissues are exposed to increases in serosal K+. A substantial part of this alkalinization in response to increases in serosal K+ (pHi 7.00 to 7.46) appears to be a HCO3- exit pathway that is independent of both Na+ and Cl-, unaffected by bumetanide or amiloride, but sensitive to DIDS. We propose the presence of a Cl(-)- and Na(+)-independent K(+)-dependent HCO3- cotransporter in Necturus oxyntopeptic cell basolateral membranes.

Animals↗