Increase In Chloride Secretion Research Articles

Modulators of Ion Transport in Nasal Polyps: An in situ Measurement of Short-Circuit Current

ObjectivesTo examine possible modulators of the ion transport through the apical membrane of the nasal polyps.MethodsThe study was conducted using the freshly-excised nasal polyps from the patients with chronic sinusitis. A voltage-sensitive vibrating probe technique was introduced to monitor the short-circuit current across the apical membrane of the polyp at 37℃.ResultsIn the presence of amiloride, Adenosine 5'-triphosphate induced 4,4'-Diisothiocyanatostilbene-2,2'-disulfonic acidsensitive chloride current. Uridine 5'-diphosphate was less potent than Uridine 5'-triphosphate, and adenosine increased chloride secretion, which was blocked by the antagonist, 8-(p-sulfophenyl) theophylline on adenosine receptor. Based on the pharmacologic profiles, multiple purinergic receptors, including P2Y2, P2Y6, and P1 receptors, were functionally expressed. However, P2X receptor agonists (α,β-methyleneadenosine 5'-triphosphate and 2'- & 3'-O-[4-benzoyl-benzoyl] adenosine 5'-triphosphate), Cystic fibrosis conductance regulator (CFTR) activator (genistein), nitric oxide substrate (L-arginine), and nitric oxide donor (sodium nitroprusside) had no significant effect on the short circuit current.ConclusionAmong tested drugs, P2Y receptor agonists were major modulators of ion transport in nasal polyps in situ.

New pulmonary therapies for cystic fibrosis

Improved knowledge of the molecular mechanisms underlying cystic fibrosis has led to a wide spectrum of new treatment approaches. This review addresses recent therapeutic strategies that either target the underlying defect or early steps in cystic fibrosis pathophysiology. While gene therapy does not appear to be a therapeutic option in the near future, cystic fibrosis transmembrane regulator pharmacotherapy is currently being developed as an alternative to reduce cystic fibrosis transmembrane regulator degradation or improve its function. Two drugs that increase chloride secretion via an alternative chloride channel, Moli1901 and denufosol, have been shown to be safe in clinical studies that also suggested clinical efficacy. Osmotic therapy may be an alternative approach to increase airway surface liquid and is being studied as an early intervention strategy. The spectrum of treatments for cystic fibrosis lung disease is rapidly increasing. While clinical efficacy for most of the compounds still has to be proven in large clinical trials, there is considerable hope that cystic fibrosis therapy will move from addressing the downstream sequelae of the cystic fibrosis transmembrane regulator defect to a more causal approach in the near future.

In vitro effects of reactive oxygen metabolites, with and without flunixin meglumine, on equine colonic mucosa

To determine effects of reactive oxygen metabolites (ROMs), with and without flunixin meglumine, on equine right ventral colon (RVC) in vitro. 18 healthy horses and ponies. In 3 groups of 6 animals each, short-circuit current and conductance were measured in RVC mucosa in Ussing chambers. The 3 groups received physiologic saline (0.9% NaCl) solution, IV, 10 minutes before euthanasia and tissue incubation in Krebs-Ringer-bicarbonate (KRB) solution; flunixin meglumine (1.1 mg/kg, IV) 10 minutes before euthanasia and tissue incubation in KRB solution; or physiologic saline solution, IV, 10 minutes before euthanasia and incubation in KRB solution with 2.7 x 10(5)M flunixin meglumine. Incubation conditions included control (no addition) and ROM systems, including addition of 1 mM xanthine and 80 mU of xanthine oxidase (to produce the superoxide radical), 1 mM H(2)O(2), and 1 mM H(2)O(2) and 0.5 mM ferrous sulfate (to produce the hydroxyl radical). All ROMs that were added or generated significantly increased the short-circuit current except in tissues coincubated with flunixin meglumine, and they induced mild epithelial vacuolation and apoptosis, but did not disrupt the epithelium nor change conductance, lactate dehydrogenase release, or [(3)H]mannitol flux. Responses to ROMs could be attributed to increased chloride secretion and inhibited neutral NaCl absorption in equine RVC, possibly by stimulating prostaglandin production. The ROMs examined under conditions of this study could play a role in prostaglandin-mediated colonic secretion in horses with enterocolitis without causing direct mucosal injury.

Dihydroxy bile acids increase mucosal permeability and bacterial uptake in human colon biopsies

Objective. Bile acids in mM concentrations are known to increase chloride secretion and alter mucosal permeability in animal colon. Increased mucosal permeability is believed to play an important role in the development of intestinal inflammation. The aim of this study was to investigate the influence of µM concentrations of dihydroxy bile acids on permeability and bacterial uptake in the normal human colon. Material and methods. Endoscopic biopsies from the sigmoid colon of 18 subjects with normal colonic histology were mounted in modified Ussing chambers. Chenodeoxycholic acid (CDCA) and deoxycholic acid (DCA) were added to the mucosal compartment. Short-circuit current (Isc) and transepithelial resistance (TER) were studied for 120 min. Cr-EDTA and horseradish peroxidase (HRP) were used to assess paracellular and transcellular permeability, respectively. The transmucosal passage of chemically killed Escherichia coli was quantified and investigated using confocal microscopy. Results. A significant decrease in TER was seen after 60 min of exposure to 1000 µmol/l CDCA and DCA. The combination of E. coli and 100 µmol/l CDCA gave a decrease in TER compared to controls (p=0.06). DCA showed a dose-related increase in Cr-EDTA permeability, which was most pronounced at 1000 µmol/l (p=0.02). Increased E. coli uptake was induced by 500 µmol/l (p=0.01) and 1000 µmol/l CDCA (p=0.04). Bacterial uptake was increased at 100 µmol/l by exposure to DCA (p=0.03). Confocal microscopy revealed the presence of E. coli bacteria in the lamina propria after 15 min of exposure to 1000 µmol/l CDCA and DCA. Conclusions. Our study suggests that dihydroxy bile acids in µM concentrations alter barrier function in normal human colon biopsies, causing increased antigen and bacterial uptake; thereby bile acids may contribute to the development of intestinal inflammation.

Hydrogen Sulfide Is a Novel Prosecretory Neuromodulator in the Guinea-Pig and Human Colon

Hydrogen sulfide (H(2)S) has been suggested as a novel gasomediator. We explored its unknown neuromodulatory role in human and guinea-pig colon. We used immunohistochemistry to detect H(2)S-producing enzymes cystathionine gamma-lyase (CSE) and cystathionine beta-synthase (CBS) in enteric neurons, Ussing chambers to measure mucosal ion secretion, and neuroimaging with voltage- and Ca(++)-sensitive dyes to record H(2)S effects on guinea-pig and human enteric neurons. More than 90% of guinea-pig and human submucous and myenteric neurons were colabeled for CSE and CBS. Myenteric interstitial cells of Cajal were CSE-immunoreactive. The exogenous H(2)S donor NaHS (0.2-2.5 mmol/L) concentration-dependently increased chloride secretion in human and guinea-pig submucosa/mucosa preparations, but not in the colonic epithelial cell line T84. The secretory response was reduced significantly by tetrodotoxin (0.5 micromol/L), capsaicin desensitization (10 micromol/L), and the transient receptor potentials vanilloid receptor 1 antagonist capsazepine (10 micromol/L). The endogenous H(2)S donor L-cysteine also induced secretion that was diminished significantly by capsaicin desensitization, the CBS inhibitor amino-oxyacetic acid, and the CSE inhibitor propargylglycine. NaHS increased spike discharge in 23% of guinea-pig and 36% of human submucous neurons, but had no effect on Ca(++) mobilization in cultured guinea-pig enteric neurons. This excitatory response was reduced significantly by capsaicin desensitization and capsazepine, but not by glibenclamide (10 micromol/L). The presence of H(2)S-producing enzymes in human and guinea-pig enteric neurons, the excitatory action on enteric neurons, and the prosecretory effects of NaHS suggest H(2)S as a novel gut-signaling molecule. Its action mainly involves transient receptor potentials vanilloid receptor 1 receptors on extrinsic afferent terminals, which in turn activate enteric neurons.

Mechanism of diarrhea in microscopic colitis

To search the pathophysiological mechanism of diarrhea based on daily stool weights, fecal electrolytes, osmotic gap and pH. Seventy-six patients were included: 51 with microscopic colitis (MC) (40 with lymphocytic colitis (LC); 11 with collagenous colitis (CC)); 7 with MC without diarrhea and 18 as a control group (CG). They collected stool for 3 d. Sodium and potassium concentration were determined by flame photometry and chloride concentration by titration method of Schales. Fecal osmotic gap was calculated from the difference of osmolarity of fecal fluid and double sum of sodium and potassium concentration. Fecal fluid sodium concentration was significantly increased in LC 58.11+/-5.38 mmol/L (P<0.01) and CC 54.14+/-8.42 mmol/L (P<0.05) than in CG 34.28+/-2.98 mmol/L. Potassium concentration in LC 74.65+/-5.29 mmol/L (P<0.01) and CC 75.53+/-8.78 mmol/L (P<0.05) was significantly less compared to CG 92.67+/-2.99 mmol/L. Chloride concentration in CC 36.07+/-7.29 mmol/L was significantly higher than in CG 24.11+/-2.05 mmol/L (P<0.05). Forty-four (86.7%) patients had a secretory diarrhea compared to fecal osmotic gap. Seven (13.3%) patients had osmotic diarrhea. Diarrhea in MC mostly belongs to the secretory type. The major pathophysiological mechanism in LC could be explained by a decrease of active sodium absorption. In CC, decreased Cl/HCO3 exchange rate and increased chloride secretion are coexistent pathways.

The spice of life for cystic fibrosis

The spice of life for cystic fibrosis

INS37217 Nasal Spray, a P2Y2 receptor agonist, as a novel treatment for common cold

Rationale This study evaluated safety, tolerability and dose regimen of a new P2Y 2 receptor agonist (INS37217) in patients with common cold symptoms. INS37217 is known to regulate mucosal hydration, increase chloride secretion and cilia beat frequency in vitro. Methods In a double-blind, parallel-group tolerability study, 101 subjects with symptoms of common cold received either 10mg/ml or 40mg/ml of INS37217 Nasal Spray or placebo (saline spray) BID or QID for 6 days. Cold symptoms were recorded daily by subjects for 14 days. Mucociliary function was evaluated by an intranasal saccharin-test on Days 0, 2, 6, and 14. Results INS37217 was well tolerated. There were consistent trends toward reduction in symptom scores in all groups of subjects receiving intranasal INS37217 compared to placebo. The INS37217 10mg/ml BID regimen significantly reduced malaise (Days 5, 8, 9, 10 and 11, p≤0.047) and post-nasal drip (Day 10, p≤0.046). At the end of treatment (Day 6), a larger proportion of subjects in the INS37217 10mg/ml group had normal mucociliary clearance (10.9 minutes for 50th percentile) compared to placebo (28.0 minutes for 50th percentile, p=0.070). Conclusion Intranasal treatment with INS37217 for 6 days was well tolerated and appeared to accelerate restoration of mucociliary clearance during colds. Enhancement of mucociliary clearance may have therapeutic value in improving symptoms during colds and possibly in reducing complications. Larger controlled studies of this intervention are warranted.

Uridine 5′-Triphosphate Stimulates Alveolar Fluid Clearance in the Isolated Rat Lungs

Uridine 5′-triphosphate (UTP) increases chloride secretion followed by fluid movement into the proximal airspaces. However, little is known about whether UTP affects fluid movement in the distal airspaces. We studied the effect of UTP on basal and stimulated alveolar fluid clearance in the isolated rat lungs. Isosmotic 5% albumin solution was instilled into the alveolar spaces of isolated rat lungs, which were then inflated with 100% oxygen at an airway pressure of 7 cmH2O. Alveolar fluid clearance was measured by the progressive increase in albumin concentrations over 1 h. Although UTP (10−9 – 10−6 M) did not increase alveolar fluid clearance, UTP (10−5 – 10−3 M) and isoproterenol (10−5 M), a β-adrenergic agonist, increased alveolar fluid clearance by 40% and 120% of the basal values, respectively. A combined treatment of UTP (10−4 M, 10−3 M) and isoproterenol increased alveolar fluid clearance by 280% of the basal value. The effects of UTP in the presence and absence of isoproterenol were abolished by blockers of a P2 purinoceptor and chloride channels. These results indicate that UTP stimulates alveolar fluid clearance in the distal airspaces of rat lungs.

The effect of caffeine on renal epithelial cells from patients with autosomal dominant polycystic kidney disease.

Autosomal dominant polycystic kidney disease (ADPKD) is a hereditary disorder characterized by the progressive enlargement of cysts derived from tubules. Tubule cell proliferation and chloride-dependent fluid accumulation, mechanisms underlying cyst expansion, are accelerated by adenosine 3':5'-cyclic monophosphate (cAMP). This study examined the extent to which caffeine may stimulate the production of cAMP by cyst epithelial cells, thereby adversely increasing proliferation and fluid secretion. Mural epithelial cells from ADPKD cysts and normal human kidney cortex cells (HKC) were cultured, and cAMP levels were determined in response to caffeine and receptor-mediated agonists linked to adenylyl cyclase. Caffeine, a methylxanthine, slightly increased basal levels of cAMP, as did other nonselective phosphodiesterase (PDE) inhibitors, 1-methyl-3- isobutyl xanthine and theophylline and rolipram, a specific PDE IV inhibitor. More importantly, clinically relevant concentrations of caffeine (10 to 50 micro M) potentiated the effects of desmopressin (DDAVP), prostaglandin E(2) (PGE(2)), and isoproterenol to increase cAMP levels in both ADPKD and HKC cells. By contrast, at concentrations that augmented the DDAVP response, caffeine attenuated cAMP accumulation by adenosine, implicating an action apart from the inhibition of PDE. Caffeine enhanced the effect of DDAVP to stimulate transepithelial short-circuit current of polarized ADPKD monolayers, reflecting an increase in chloride secretion. Caffeine potentiated the effect of DDAVP and PGE(2) to increase the levels of phosphorylated extracellular signal-regulated kinase (P-ERK). By contrast, P-ERK levels in HKC cells were not raised by increased intracellular concentrations of cAMP. It is concluded that PDE inhibition by caffeine increases the accumulation of cAMP, and through this mechanism activates the ERK pathway to cellular proliferation and increases transepithelial fluid secretion in ADPKD cystic epithelium. Caffeine is, therefore, a risk factor for the promotion of cyst enlargement in patients with ADPKD.

Changes in chloride secretion rate and vascular perfusion in the rectal gland of the European lesser‐spotted dogfish in response to environmental and hormonal stimuli

Chloride secretion rates of rectal glands taken from the European lesser‐spotted dogfish Scyliorhinus canicula adapting to 70% and 120% sea water (SW) were significantly greater and less than, respectively, those in the control 100% SW group. C‐type natriuretic peptide (CNP) significantly increased chloride secretion rates above basal values in 100% SW although angiotenisn II (ANG II) had no effect. Perfusion of the secretory epithelia in rectal glands from 70% SW lesser‐spotted dogfish was significantly higher than in rectal glands from 100% and 120% SW lesser‐spotted dogfish. Perfusion of rectal glands with ANG II had no effect on perfusion of the secretory epithelia, although CNP perfusion induced significantly greater perfusion of the secretory epithelia than all other treatments. It remains to be determined if a reduction in environmental salinity induces an increase in plasma concentration of CNP and hence an increase in rectal gland activity.

Changes in chloride secretion rate and vascular perfusion in the rectal gland of the European lesser-spotted dogfish in response to environmental and hormonal stimuli

Chloride secretion rates of rectal glands taken from the European lesser-spotted dogfish Scyliorhinus canicula adapting to 70% and 120% sea water (SW) were significantly greater and less than, respectively, those in the control 100% SW group. C-type natriuretic peptide (CNP) significantly increased chloride secretion rates above basal values in 100% SW although angiotenisn II (ANG II) had no effect. Perfusion of the secretory epithelia in rectal glands from 70% SW lesser-spotted dogfish was significantly higher than in rectal glands from 100% and 120% SW lesser-spotted dogfish. Perfusion of rectal glands with ANG II had no effect on perfusion of the secretory epithelia, although CNP perfusion induced significantly greater perfusion of the secretory epithelia than all other treatments. It remains to be determined if a reduction in environmental salinity induces an increase in plasma concentration of CNP and hence an increase in rectal gland activity.

Phosphatidylinositol 3-Kinase-dependent Pathways Oppose Fas-induced Apoptosis and Limit Chloride Secretion in Human Intestinal Epithelial Cells: IMPLICATIONS FOR INFLAMMATORY DIARRHEAL STATES

The epithelial lining of the intestine serves as a barrier to lumenal bacteria and can be compromised by pathologic Fas-mediated epithelial apoptosis. Phosphatidylinositol (PI)3-kinase signaling has been described to limit apoptosis in other systems. We hypothesized that PI3-kinase-dependent pathways regulate Fas-mediated apoptosis and barrier function in intestiynal epithelial cells (IEC). IEC lines (HT-29 and T84) were exposed to agonist anti-Fas antibody in the presence or absence of chemical inhibitors of PI3-kinase (LY294002 and wortmannin). Apoptosis, barrier function, changes in short circuit current (DeltaI(sc)), and expression of adhesion molecules were assessed. Inhibition of PI3-kinase strongly sensitized IEC to Fas-mediated apoptosis. Expression of constitutively active Akt, a principal downstream effector of the PI3-kinase pathway, protected against Fas-mediated apoptosis to an extent that was comparable with expression of a genetic caspase inhibitor, p35. PI3-kinase inhibition sensitized to apoptosis by increasing and accelerating Fas-mediated caspase activation. Inhibition of PI3-kinase combined with cross-linking Fas was associated with increased permeability to molecules that were <400 Da but not those that were >3,000 Da. Inhibition of PI3-kinase resulted in chloride secretion that was augmented by cross-linking Fas. Confocal analyses revealed polymerization of actin and maintenance of epithelial cell adhesion molecule-mediated interactions in monolayers exposed to anti-Fas antibody in the context of PI3-kinase inhibition. PI3-kinase-dependent pathways, especially Akt, protect IEC against Fas-mediated apoptosis. Inhibition of PI3-kinase in the context of Fas signaling results in increased chloride secretion and barrier dysfunction. These findings suggest that agonists of PI3-kinase such as growth factors may have a dual effect on intestinal inflammation by protecting epithelial cells against immune-mediated apoptosis and limiting chloride secretory diarrhea.

Effect of linear alkylbenzene sulfonate (LAS) on ion transport and intracellular calcium in kidney distal epithelial cells (A6)

Linear alkylbenzene sulfonate (LAS) is found in near-shore environments receiving wastewater from urban treatment plants in a concentration reported to have physiological and toxic effect on aquatic organisms. The aim of this study was to investigate the effect LAS on ion transport and homeostasis in epithelia cells. A6 cells form a polarised epithelium when grown on permeable supports, actively absorb sodium and secrete chloride. Only the addition of LAS (100 μ m) to the apical solution of A6 epithelia resulted in an increase in the active ion transport measured as short circuit current (SCC) and transepithelial conductance (G t). This increase could not be affected by the sodium channel inhibitor amiloride (100 μ m), indicating that LAS stimulated the chloride secretion. Change in the intracellular calcium concentration (Ca 2+) i was measured in fura-2 loaded A6 cells, since it known that increase in (Ca 2+) i stimulate chloride secretion. LAS induced a concentration-dependent increase in (Ca 2+) i from 5 to 200 μ m, where the half-maximal stimulating concentration on 100 m m resulted in an increase in (Ca 2+) i from 108±15 to 570±26 n m ( n=4; P<0.01). The increase in (Ca 2+) i could be blocked by the calcium chelator ethylenebis(5-oxyethylenenitrilo)tetraacetic acid (EGTA), showing that the effect of LAS was due to influx of extracellular calcium. Furthermore, it was shown that the calcium channel inhibitor verapamil (0.2 m m) abolished the LAS induced increase in (Ca 2+) i and Gt when applied to the apical solution. However, verapamil has no inhibitory effect on these parameters when the non-ionic detergent Triton X-100 (100 μ m) was added to A6 cells. These results indicate that LAS induced a specific activation of calcium channels in the apical membrane of A6 epithelia, leading to increase in (Ca 2+) i and thereby increased chloride secretion as a result of stimulation of calcium-dependent chloride channels in the apical membrane. The change in ion homeostasis is thought to be the fundamental reason to the physiological and toxic effects induced by LAS in marine organism.

EBIO, an agent causing maintained epithelial chloride secretion by co-ordinate actions at both apical and basolateral membranes.

The effect of 1-ethyl-2-benzimidazolone (EBIO) on electrogenic chloride secretion in murine colonic and nasal epithelium was investigated by the short-circuit technique. In the colon, EBIO produces a sustained current increase in the presence of amiloride, which is sensitive to furosemide. In nasal epithelium EBIO causes only a small, transient current increase. Sustained increases in current were obtained in response to forskolin in both epithelia. To examine the mechanisms by which EBIO increases chloride secretion, the effects on intracellular mediators were measured in colonic crypts. There was no effect on [Ca(2+)]i but cAMP content was increased, more so in the presence of IBMX, indicating a direct effect on adenylate cyclase. In colonic epithelia in which the apical surface was permeabilized by nystatin, and the tissue subjected to an apical to basolateral K(+) gradient, EBIO caused a current increase that was entirely sensitive to charybdotoxin (ChTX). In similarly permeabilized colons Br-cAMP caused a current increase that was entirely sensitive to 293B. Thus EBIO increases chloride secretion in the colon by coordinated actions at both the apical and basolateral faces of the cells. These include direct and indirect actions on Ca(2+)-sensitive and cAMP-sensitive K(+) channels respectively, and indirect actions on the basolateral cotransporter and apical CFTR chloride channels via cAMP. In CF colonic epithelia EBIO did not evoke chloride secretion. It is not clear why the nasal epithelium responds poorly to EBIO whereas it gives a sustained response to the related compound chlorzoxazone.

Pharmacological treatment of the biochemical defect in cystic fibrosis airways.

The understanding of the biochemical defect in cystic fibrosis (CF) has advanced considerably since discovery of the CF gene in 1989 and characterization of its product. Studies showing that the abnormality in chloride flux could be corrected by transfection of wild-type cystic fibrosis transmembrane conductance regulator (CFTR) complimentary deoxyribonucleic acid (cDNA) have led to gene therapy trials on both sides of the Atlantic. However, gene therapy as a treatment for CF has yet to be realized. Pharmacological manipulation of the biochemical defect may provide an alternative or complementary approach to treatment. This review will discuss pharmacological agents in development which could correct the abnormal ion movement. The mechanisms of action of these pharmacological agents can be divided broadly into drugs which affect the most common CF mutation, deltaF508, which increase trafficking of the mutant CF protein to the apical membrane; drugs which increase chloride secretion; and drugs which reduce sodium reabsorption across the apical membrane. Treatment options for cystic fibrosis have developed rapidly since discovery of the cystic fibrosis gene over a decade ago. The targeting of specific therapies for particular cystic fibrosis genotypes and the use of combination treatments of chloride channel openers with sodium channel blockers are likely to be key advances in the next decade.

PI3'-kinase- and fas-dependent pathways regulate apoplosis, barrier function and chloride secretion in intestinal epithelial cells (IEC): Implications for inflammatory diarrheal states

BACKGROUND/OBJECTIVES: The epithelial lining of the intestine serves as a critical barrier to lumenal bacteria and may be compromised by pathotogic Fas-mediated IEC apoptosis. Phosphatidylinositol (PI)3'-kinase has been described to limit apoptosis in other systems. We hypothesized that PI3'-kinase dependent pathways regulate Fas-mediated apoptosis and barrier function in IEC. METHODS: lEO lines (HT-29, T84) were exposed to agonist anti-Fas Ab in the presence or absence of chemical inhibitors of PI3'-kinase (LY294002, wortmannin). Apoptosis, barrier function, short-circuit current (Alsc) and expression of adhesion molecules were assessed. RESULTS: Inhibition of PI3'-kinase strongly sensitized lEG to Fas-mediated apoptosis. Inhibition of PI3'-kinase combined with cross-linking Fas was associated with barrier dysfunction ()transepithelial electrical resistance (TER), permeability). Confocal analyses revealed disruption of actin and adhesion/junctional molecules (EpCAM, E-cadherin, ZO-1, desmoplakin) in monolayers exposed to anti-Fas Ab in the context of PI3'-kinase inhibition. Caspase inhibition prevented apoptosis in response to cross-linking Fas in the presence or absence of PI3'-kinase inhibitors. In spite of preventing apoptosis, caspase inhibition did not effect PI3'-kinase-dependent changes in TER. To explore additional mechanisms for diminished TER, we measured changes in Isc in T84 monolayers. Whereas cross-linking Fas alone had no effect on L~Isc, cross-linking Fas in the presence of LY294002 led to synergistic increases in L~Isc consistent with increased CIsecretion. To determine downstream effectors mediating PI3'-kinase-dependent protection from Fas-mediated apoptosis, we expressed constitutivelyactive Akt, a principal downstream effector of the PI3'-kinase pathway. Akt protected against Fas-mediated apoptosis to an extent that was comparable to expression of a genetic caspase inhibitor p35. CONCLUSIONS: PI3'-kinase-dependent pathways, especially Akt, protect IEC against Fas-mediatad apoptosis. Inhibition of PI3'-kinase in the context of Fas signaling results in increased chloride secretion. These findings suggest that agonists of PI3'-kinase such as growth factors may have a dual effect on intestinal inflammation by protecting epithelial cells against immune-mediated apoptosis and limiting chloride secretory diarrhea.

Rotavirus infection induces increased chloride secretion, altered barrier function and epidermal growth factor receptor (EGF-R) polyubiquitination in intestinal epithelial cells (IEC)

Rotavirus infection induces increased chloride secretion, altered barrier function and epidermal growth factor receptor (EGF-R) polyubiquitination in intestinal epithelial cells (IEC)

Rotavirus infection induces increased chloride secretion, altered barrier function and epidermal growth factor receptor (EGF-R) polyubiquitination in intestinal epithelial cells (IEC)

Rotavirus infection induces increased chloride secretion, altered barrier function and epidermal growth factor receptor (EGF-R) polyubiquitination in intestinal epithelial cells (IEC)

Role of Nutrients and Bacterial Colonization in the Development of Intestinal Host Defense

In this introduction to the supplement on the use of pre- and probiotics in the health and disease of pediatric patients, I have summarized factors affecting the initial colonization of the neonatal intestine. The term bacterial-epithelial cross-talk was defined, and examples of the enterocyte response to both pathologic and indigenous flora stimulation illustrated. Immaturities in the human neonatal intestinal response to bacteria and their toxins were reviewed in the context of the pathogenesis of age-specific, bacterial gastrointestinal infectious diseases. Finally, the importance of pre- and probiotics as measures to strengthen the neonate's intestinal host defenses in the prevention and treatment of specific age-related disease were considered.