Contribution of villus and intervillus epithelium to intestinal transmural potential difference and response to theophylline and sugar.

A chamber design is described which permits isolation of villus or intervillus epithelium from proximal segments of Amphiuma intestine and measurement of the transpithelial potential difference (psi ms) and short-circuit current (Isc) produced by each. In media containing Cl- and 10 mequiv./l HCO3- the villus generated a basal psi ms of 0.8 mV (serosa negative) and Isc of 12 microA/cm2 while the intervillus psi ms and Isc were not different from zero. Acetazolamide altered the villus psi ms by 1.2 mV; the intervillus psi ms by only 0.3 mV. Transepithelial gradients of HCO3- appeared to generate diffusion potentials across the intervillus but not the villus epithelium. The actively transported sugar galactose elevated psi ms by 0.6 +/- 0.1 mV in the intervillus epithelium and by 1.5 +/- 0.2 mV in the villus epithelium for a response ratio (0.6/1.5) = 0.4. The response ratio for valine was 0.3. In contrast, the response ratios for theophylline (0.7) and cyclic AMP (0.7) were significantly higher. These observations indicate that the entire epithelium is responsive to theophylline and cyclic AMP while Na+-dependent solute transport and the basal electrogenic ion transport processes are primarily functions of the cells lining the intestinal villus.     

Calcium modulation of the effects of serotonin,carbachol, and histamine on rabbit ileal ion transport.

In mammalian intestine, a number of secretagogues have been shown to work through either cyclic nucleotide or calcium mediated pathways to elicit ion secretion. Because excessive intestinal electrolyte and fluid secretion is central to the pathogenesis of a variety of diarrheal disorders, understanding of these processes is essential to the development of future clinical treatments. In the current study, the effects of serotonin (5HT), histamine, and carbachol on intestinal ion transport were examined in in vitro preparations of rabbit ileum. All three agonists induced a rapid and transient increase short-circuit current (delta Isc) across ileal mucosa. Inhibition of the delta Isc response of all three agents in chloride-free solution or in the presence of bumetanide confirmed that chloride is the main electrolyte involved in electrogenic ion secretion. Pretreatment of tissue with tetrodotoxin or atropine did not effect secretagogue-mediated electrolyte secretion. While tachyphylaxis of delta Isc response was shown to develop after repeated exposure of a secretagogue to tissue, delta Isc responses after sequential addition of different agonists indicate that cross-tachyphylaxis between agents did not occur. Serotonin, histamine, and carbachol have previously been reported to mediate electrolyte secretion through calcium-dependent pathways. To access the role of extracellular calcium in regulating ion secretion, the effect of verapamil on each agent was tested; verapamil decreased 5HT-induced delta Isc by 65.2% and histamine response by 33.5%, but had no effect on carbachol-elicited chloride secretion. An additive secretory effect was found upon simultaneous exposure of 5HT and carbachol to the system; no other combination of agents produced a significant additive effect. Findings from this study support previous work which has suggested that multiple calcium pathways may be involved in mediating chloride secretion in mammalian intestine.     

The identity of the current carriers in canine lingual epithelium in vitro

Ion transport across the lingual epithelium has been implicated as an early event in gustatory transduction. The fluxes of isotopically labelled Na+ and Cl- were measured across isolated canine dorsal lingual epithelium under short-circuit conditions. The epithelium actively absorbs Na+ and to a lesser extent actively secretes Cl-. Under symmetrical conditions with Krebs-Henseleit buffer on both sides, (1) Na+ absorption accounts for 46% of the short-circuit current (Isc); (2) there are two transcellular Na+ pathways, one amiloride-sensitive and one amiloride-insensitive; (3) ouabain, added to the serosal solution, inhibits both Isc and active Na+ absorption. When hyperosmotic (0.25 M) NaCl is placed in the mucosal bath, both Isc and Na+ absorption increase; net Na+ absorption is at least as much as Isc. Ion substitution studies indicate that the tissue may transport a variety of larger ions, though not as effectively as Na+ and Cl-. Thus we have shown that the lingual epithelium, like other epithelia of the gastrointestinal tract, actively transports ions. However, it is unusual both in its response to hyperosmotic solutions and in the variety of ions that support a transepithelial short-circuit current. Since sodium ion transport under hyperosmotic conditions has been shown to correlate well with the gustatory neural response, the variety of ions transported may likewise indicate a wider role for transport in taste transduction.     

Evidence for substance P as a functional neurotransmitter in guinea pig small intestinal mucosa

We showed previously that electrical transmural stimulation (TS) of guinea pig jejunal mucosa in vitro released neurotransmitters from submucosal plexus neurons which caused alterations in ion transport. The present studies were performed to obtain information regarding the identity of the neurotransmitters. The addition of exogenous substance P (SP) to the serosal side of the tissue caused a transient increase in short-circuit current (Isc) which closely mimicked the response to TS. Both TS and SP caused net secretion of Cl- ions by stimulating movement toward the luminal side. Tetrodotoxin abolished the response to TS, inhibited approximately 70% of the response to SP but did not affect the response to urecholine, a cholinergic muscarinic agonist. In the presence of the muscarinic antagonist, atropine, Isc responses to both TS and SP were reduced suggesting that a portion of both responses was due to action on enteric nerves causing release of acetylcholine. Following desensitization of the tissue with supramaximal doses of SP the response to TS was significantly reduced but the response to urecholine was unchanged. In the presence of atropine, SP desensitization reduced the nerve-stimulated response by approximately 65%; treatment of tissue with SP antibodies reduced the response by approximately 55%. Under the same conditions Isc responses to histamine were unaltered. Our results suggest that both SP (or a structurally analogous neurotransmitter) and acetylcholine as well as additional unidentified neurotransmitter(s) are functionally important in the regulation of intestinal ion transport in guinea pig jejunum.     

Trichinella spiralis: evidence that mice do not express rapid expulsion.

The rapid expulsion of Trichinella spiralis by mice of a variety of inbred and F1 mouse strains was examined. Mice were reinfected once with T. spiralis during and immediately after the natural termination of a primary infection and worm rejection was measured less than or equal to 24 hr after the challenge. The results showed that the challenge (super)infection was consistently rejected by all mouse strains before rejection of the adult worms from the primary infection commenced. Rejection of the challenge infection began at different times after the primary infection with NFS (2 days) less than C3H less than or equal to B10.Q approximately B10.BR (greater than 5 days). In all strains, rejection of the challenge infection preceded adult worm rejection from the primary infection by 5-8 days. At its peak, the loss of challenge worms related directly to the strength of the primary rejection process NFS greater than or equal to 98%, C3H 90-98%, and B10 mice 80-90%. Furthermore, loss of the capacity to reject the challenge followed approximately 7 days after the complete loss of the primary infection in each strain examined. Thus, the sooner worms from the primary infection were lost, the earlier the capacity to promptly reject the challenge infection disappeared. B10.Br mice still partially rejected a superinfection 35 days after the primary infection began, whereas NFS mice lost this capacity around 25 days. However, premature termination of the primary infection in B10.BR mice with methyridine at the same time that NFS mice naturally terminated their infection (15 days) abrogated the capacity of B10.BR mice to reject the superinfection at 24 days. Passive transfer of protective rat IgG monoclonal antibody to mice did not lead to rapid expulsion. Transfer of mouse immune serum to intestinally primed rats did result in rapid expulsion, suggesting that mouse antibody responses were adequate. The expression of superinfection rejection was susceptible to the administration in vivo of GK1.5, anti-mouse L3T4 antibody. The data indicate that the principal determinant of the strength, time of initiation, and longevity of rejection of a challenge infection was the response to the primary infection of that individual mouse strain. The genetic determinants of challenge infection rejection were seen to be identical to those that determined rejection of the primary infection. Since no evidence could be found to support the identity of this response with rapid expulsion, as defined in rats, a new term, "associative expulsion," is proposed.(ABSTRACT TRUNCATED AT 400 WORDS)     

Nitric oxide decreases intestinal haemorrhagic lesions in rat anaphylaxis independently of mast cell activation

The purpose of this study is to assess the role of nitric oxide (NO) in the intestinal lesions of passive anaphylaxis, since this experimental model resembles necrotizing enterocolitis. Sprague-Dawley rats were sensitized with IgE anti-dinitrophenol monoclonal antibody. Extravasation of protein-rich plasma and haemorrhagia were measured in the small intestine. Plasma histamine was measured to assess mast cell activation. The effect of exogenous NO on the lesions was assessed by using two structurally unrelated NO-donors: sodium nitroprusside and S-nitroso-Nacetyl-penicillamine (SNAP). An increased basal production of NO was observed in cells taken after anaphylaxis, associated with a reduced response to platelet-activating factor, interleukin 1beta, and IgE/DNP-bovine serum albumin complexes. The response to bacterial lipopolysaccharide and dibutyryl cyclic adenosine monophosphate (AMP) was enhanced 24 h after challenge, but at earlier times was not significantly different from that observed in controls. Treatment with either sodium nitroprusside or SNAP produced a significant reduction of the haemorrhagic lesions, which are a hallmark of rat anaphylaxis. The extravasation of protein-rich plasma was not influenced by NO-donors. The increase of plasma histamine elicited by the anaphylactic challenge was not influenced by SNAP treatment. NO-donors protect intestinal haemorrhagic lesions of rat anaphylaxis by a mechanism apparently independent of mast cell histamine release.     

Effects of Enterococcus faecium NCIMB 10415 as probiotic supplement on intestinal transport and barrier function of piglets

Many studies report positive effects of probiotic supplementation on the performance and health of piglets. The intention of this study was to describe the effects of Enterococcus faecium NCIMB 10415 on the transport and barrier functions of pig small intestine to improve our understanding of the underlying mechanisms of this probiotic. Ussing chamber studies were conducted with isolated jejunal epithelia of piglets at the age of 14, 28, 35 and 56 days. Jejunal tissues of the control group were compared with epithelia of piglets that had received a diet supplemented with the probiotic Enterococcus faecium NCIMB 10415. Transport properties (absorption and secretion) of the epithelia were examined by mucosal addition of glucose or L-glutamine or by serosal addition of PGE2. Electrophysiology of the epithelia was continuously recorded and the change in short circuit current (Isc) was determined. Paracellular permeability was measured by measuring the flux rates of mannitol. The increase of Isc caused by mucosal addition of glucose was, at all glucose concentrations, higher in the probiotic group compared with the control group. However, the difference (up to 100% of the control) was not significant. The increase of Isc after the mucosal addition of L-glutamine (12mmol/l) was higher in the tissues of the probiotic group but did not reach significance. Serosal PGE2 induced a significantly higher increase of Isc in tissues of the probiotic group at the age of 28 days. No consistent differences were observed in mannitol transport rates between the feeding groups. Significant age-dependent alterations of absorptive and secretory properties of the jejunal epithelium were observed; these were independent of the treatment. A probiotic supplementation seems to influence transport properties of small intestine epithelium. The increased absorption of glucose could be interpreted as a positive effect for the animal.     

Trichinella spiralis: differences between "early" and "late" rapid expulsion evident from inhibition studies using cortisone and irradiation

Cortisone administered once at 100 mg/kg during the first 3 weeks of infection inhibited rapid expulsion. In rats immunized with an abbreviated infection (T/M regime) inhibition averaged approximately 50%, whereas in rats given a complete infection (C.I.) 14% inhibition occurred. Sensitivity to 400 rad whole-body irradiation was greatest 7 days before a challenge infection in all immune rats. Three days after beginning the T/M infection rats were highly susceptible to cortisone but only weakly so to irradiation. Rats immunized by C.I. were equally, but only weakly, susceptible to either cortisone or irradiation 3 days after infection. Acute administration of cortisone 1 or 4 hr prior to challenge did not inhibit rapid expulsion but 60% inhibition occurred when cortisone was given 24 hr prior to challenge. Inhibition of rapid expulsion by irradiation 7 days prior to challenge was not reversed by immune serum and irradiation did not affect antibody titer in treated rats. It was suggested that irradiation 7 days before challenge compromised the intestinal, and not the immunological, component of rapid expulsion. Differences in sensitivity of "early" and "late" rapid expulsion to irradiation and cortisone therapy provide further evidence of functional differences between these rejection processes.     

Bioelectric properties and ion flow across excised human bronchi

Bioelectric properties and ion transport of excised human segmental/subsegmental bronchi were measured in specimens from 40 patients. Transepithelial electric potential difference (PD), short-circuit current (Isc), and conductance (G), averaged 5.8 mV (lumen negative), 51 microA X cm-2, and 9 mS X cm-2, respectively. Na+ was absorbed from lumen to interstitium under open- and short-circuit conditions. Cl- flows were symmetrical under short-circuit conditions. Isc was abolished by 10(-4) M ouabain. Amiloride inhibited Isc (the concentration necessary to achieve 50% of the maximal effect = 7 X 10(-7) M) and abolished net Na+ transport. PD and Isc were not reduced to zero by amiloride because a net Cl- secretion was induced that reflected a reduction in Cl- flow in the absorptive direction (Jm----sCl-). Acetylcholine (10(-4) M) induced an electrically silent, matched flow of Na+ (1.7 mueq X cm-1 X h-1) and Cl- (1.9 mueq X cm-12 X h-1) toward the lumen. This response was blocked by atropine. Phenylephrine (10(-5) M) did not affect bioelectric properties or unidirectional ion flows, whereas isoproterenol (10(-5) M) induced a small increase in Isc (10%) without changing net ion flows significantly. We conclude that 1) Na+ absorption is the major active ion transport across excised human bronchi, 2) Na+ absorption is both amiloride and ouabain sensitive, 3) Cl- secretion can be induced by inhibition of the entry of luminal Na+ into the epithelia, and 4) cholinergic more than adrenergic agents modulate basal ion flow, probably by affecting gland output.     

Actions of neuropeptide Y on basal, cyclic AMP-induced and neurally evoked ion transport in porcine distal jejunum

Neuropeptide Y (NPY) and its homolog, peptide YY, are present respectively in neurons and endocrine cells within the mammalian small intestine. In this study, we examined the actions of NPY on ion transport in the porcine distal jejunum mucosa-submucosa in vitro. Peptide YY and NPY were equieffective in producing rapid and sustained decreases in basal short-circuit current (Isc), a bioelectrical measure of active ion transport, eliciting half-maximal decreases at respective serosal concentrations of 0.8 and 30 nmol/l. NPY-induced changes in Isc were due to increased mucosa-to-serosa and net Cl fluxes and were not affected by the absence of extracellular HCO3 ions. NPY activity was correlated with the magnitude of the basal Isc and appeared to depend on the spontaneous production of eicosanoids. The peptide also decreased Isc stimulated by forskolin and 8-bromo-cyclic AMP, but the ionic bases for this effect were complex and differed from those determined under basal conditions. NPY attenuated increases in Isc produced by electrical stimulation of enteric neurons with an IC50 = 5 nmol/l. The actions of the peptide on basal and cyclic AMP-induced ion transport were abolished by the neuronal conduction blocker tetrodotoxin, but not by the opiate antagonist naloxone. The alpha-adrenoceptor blocker phentolamine diminished the effects of NPY on basal, but not cyclic AMP-induced Isc. These results indicate that NPY is capable of modulating NaCl transport in the porcine jejunal mucosa under several different conditions. Furthermore, the effects of the peptide are mediated in part through noradrenergic nerves as well as enteric neurons of unknown chemical identity.     

Immunological sensitization of opossum gallbladder by naturally acquired stomach roundworm infection.

1. The opossum gallbladder develops an immediate type hypersensitivity as a result of chronic infection with the gastric nematode, Physaloptera turgida. 2. Hypersensitization is evident from a change in net transepithelial ion transport in response to parasite-derived antigen. 3. The antigen-induced change in ion transport involves mediation by histamine and possibly prostaglandins and is independent of intrinsic neural modulation. 4. The functions of the gallbladder epithelium are influenced by reactions of local immune elements that are part of the common mucosal immune system.     

Stimulating effects of dopamine on chloride transport across the rat caudal epididymal epithelium in culture

The present study investigated the effects of dopamine on chloride transport across cultured rat caudal epididymal epithelium. The results showed that dopamine induced a biphasic short-circuit current (Isc) in a concentration-dependent manner. The dopamine-induced response consisted of an initial rapid spike followed by a sustained phase. The alpha and beta adrenoreceptor inhibitors, phentolamine and propranolol, inhibited the initial spike and the sustained phase, respectively, suggesting a contribution of adrenergic receptors. The response was almost abolished by removing the extracellular Cl-, suggesting that the dopamine-induced short-circuit current is primarily a Cl- current. The response was inhibited by the apical Cl- channel blocker, diphenylamine-dicarboxylic acid, and the Ca2+-activated Cl- channel blocker, disulfonic acid stilbene, indicating that Cl- may pass through two types of Cl- channels on the apical side. Preloading monolayers with the intracellular Ca2+ chelator BAPTA/AM abolished the initial spike and greatly reduced the second phase in the Isc response to dopamine. Pretreating the monolayers with an adenylate cyclase inhibitor, MDL12330A, inhibited all of the second Isc response and part of the initial spike. Also, characteristics of the Cl- currents induced by dopamine were observed in whole-cell patch-clamp recording. The increases of intracellular cAMP and Ca2+ induced by dopamine were also measured. The results suggest that extracellular dopamine activates Ca2+-dependent and cAMP-dependent regulatory pathways, leading to activation of both Ca2+-dependent and cAMP-dependent Cl- conductances in epididymal epithelial cells.     

Trichinella spiralis: Characterization and strain distribution of rapid expulsion in inbred mice

Appropriately immunized mice display a response that is biologically equivalent to rat rapid expulsion. Only two inbred strains ($\text{NFR}\text{N}\text{and}\text{NFS}\text{N}$ derived from NIH Swiss mice) have been shown to respond in this manner. Mice of the $\text{Balb}\text{c}$, CBA, $\text{A}\text{He}$, C₃H, SJL, or C₅₇Bl strains are “nonresponders” which require approximately twice as much intestinal exposure (in days) to Trichinella spiralis to elicit a response half as effective. Genetically, the responder is dominant, autosomal, and does not appear to be linked to the MHC. The characteristics of mouse and rat rapid expulsion of T. spiralis are not identical but share these features: initial rejection within 24 hr of challenge; a rejection efficiency >90%, from 1 to 5 weeks after the primary; induction of response does not require exposure to the complete infection; rapid expulsion is immunologically specific for preadults; adult worms are resistant. While a genetic basis for responsiveness exists in mice there is, as yet, no evidence for genetic control in rats. In both mice and rats, rapid expulsion is distinguished from the intestinal hyperreactivity associated with rejection of the primary infection by the kinetics and amplitude of the rejection of transplanted adult worms.     

The apparent inability of cyprinid fish to produce skin-sensitizing antibody

Both egg albumin and horse serum failed to induce systemic anaphylactic shock in cyprinid fish. The production of skin-sensitizing antibody by these fish to either horse serum, egg albumin or antigenic extracts of the cestode, Caryophyllaeus laticeps or the acantho-cephalan, Pomphorhynchus laevis , could not be demonstrated by homologous passive cutaneous anaphylaxis (PCA) or by heterologous PCA reaction in guinea-pigs. It was considered therefore, that fish are unable to produce such antibody, at least in response to these antigens, and that it is unlikely that skin-sensitizing antibody is involved in the rejection of C. laticeps by dace Leuciscus lueciscus (L.). The phylogenetic origins of skin-sensitizing antibody are discussed.     

Oral gene delivery with chitosan--DNA nanoparticles generates immunologic protection in a murine model of peanut allergy

Food allergy is a common and often fatal disease with no effective treatment. We describe here a new immunoprophylactic strategy using oral allergen-gene immunization to modulate peanut antigen-induced murine anaphylactic responses. Oral administration of DNA nanoparticles synthesized by complexing plasmid DNA with chitosan, a natural biocompatible polysaccharide, resulted in transduced gene expression in the intestinal epithelium. Mice receiving nanoparticles containing a dominant peanut allergen gene (pCMVArah2) produced secretory IgA and serum IgG2a. Compared with non-immunized mice or mice treated with 'naked' DNA, mice immunized with nanoparticles showed a substantial reduction in allergen-induced anaphylaxis associated with reduced levels of IgE, plasma histamine and vascular leakage. These results demonstrate that oral allergen-gene immunization with chitosan-DNA nanoparticles is effective in modulating murine anaphylactic responses, and indicate its prophylactic utility in treating food allergy.     

Intracellular pH controls cell membrane Na+ and K+ conductances and transport in frog skin epithelium

We determined the effects of intracellular respiratory and metabolic acid or alkali loads, at constant or variable external pH, on the apical membrane Na+-specific conductance (ga) and basolateral membrane conductance (gb), principally due to K+, in the short-circuited isolated frog skin epithelium. Conductances were determined from the current-voltage relations of the amiloride-inhibitable cellular current pathway, and intracellular pH (pHi) was measured using double barreled H+-sensitive microelectrodes. The experimental set up permitted simultaneous recording of conductances and pHi from the same epithelial cell. We found that due to the asymmetric permeability properties of apical and basolateral cell membranes to HCO3- and NH+4, the direction of the variations in pHi was dependent on the side of addition of the acid or alkali load. Specifically, changing from control Ringer, gassed in air without HCO3- (pHo = 7.4), to one containing 25 mmol/liter HCO3- that was gassed in 5% CO2 (pHo = 7.4) on the apical side caused a rapid intracellular acidification whereas when this maneuver was performed from the basolateral side of the epithelium a slight intracellular alkalinization was produced. The addition of 15 mmol/liter NH4Cl to control Ringer on the apical side caused an immediate intracellular alkalinization that lasted up to 30 min; subsequent removal of NH4Cl resulted in a reversible fall in pHi, whereas basolateral addition of NH4Cl produced a prolonged intracellular acidosis. Using these maneouvres to change pHi we found that the transepithelial Na+ transport rate (Isc), and ga, and gb were increased by an intracellular alkalinization and decreased by an acid shift in pHi. These variations in Isc, ga, and gb with changing pHi occurred simultaneously, instantaneously, and in parallel even upon small perturbations of pHi (range, 7.1-7.4). Taken together these results indicate that pHi may act as an intrinsic regulator of epithelial ion transport.     

Synergistic interaction between immune serum and thoracic duct cells in the adoptive transfer of rapid expulsion of Trichinella spiralis in adult rats

Rapid expulsion of Trichinella spiralis could be transferred to naive adult rats with thoracic duct lymphocytes and immune serum. Thoracic duct cells collected from Days 3-5 and immune serum collected on Day 28, respectively, after infection were effective. Both cells and serum were unable to transfer rapid expulsion when given alone, even in large volumes. Recipients of immune serum and cells eliminated a significantly higher number of larvae than control rats by 1 hr after challenge with muscle larvae. Rapid expulsion produced 30-80% larval worm rejection but could not be increased by the transfer of more cells or immune serum. Mucus trappings did not appear to play a role in the rejection process. After transfer of 2 x 10(8) cells and 4.0 ml immune serum, rapid expulsion persisted for less than 1 week. However, after adoptive transfer of cells alone, the gut remained functionally receptive to the passive transfer of immune serum for 7 weeks. Therefore, the changes effected by transfer of cells were long lived in contrast to the 1 week, or less, of functional persistence by transferred immune serum. The data indicate that two separate processes, one cell mediated and the other immune serum mediated, interact synergistically in the intestine and lead to the expression of rapid expulsion.     

Bile salt alteration of ion transport across jejunal mucosa.

The effect of conjugated dihydroxy and trihydroxy bile salts on electrolyte transport across isolated rabbit jejunal mucosa was studied. Both taurochenodeoxycholic acid and taurocholic acid increased the short-circuit current (Isc) in bicarbonate-Ringer solution but not in a bicarbonate-free, chloride-free solution. Taurochenodeoxycholic acid was significantly more effective than taurocholic acid in increasing Isc. The presence of theophylline prevented the taurochenodeoxycholic acid- and taurocholic acid-induced increase in Isc. Transmural ion fluxes across jejunal mucosa demonstrated that 2 mM taurochenodeoxycholic acid decreased net Na+ absorption, increased net Cl- secretion and increased the residual flux (which probably represents HCO3- secretion). These studies support the hypothesis that cyclic AMP may be a mediator of intestinal electrolyte secretion.     

Prolonged interferon-gamma exposure decreases ion transport,NKCC1, and Na+-K+-ATPase expression in human intestinal xenografts in vivo

IFN-gamma is elevated in intestinal inflammation and alters barrier and transport functions in human colonic epithelial cell lines, but its effects on normal human small intestinal epithelium in vivo are poorly defined. We investigated effects of prolonged IFN-gamma exposure on ion transport and expression of transporters by using human fetal small intestinal xenografts. Xenograft-bearing mice were injected with IFN-gamma, and 24 h later xenografts were harvested and mounted in Ussing chambers. Baseline potential difference (PD) was not affected by IFN-gamma treatment. However, conductance was enhanced and agonist-stimulated ion transport was decreased. IFN-gamma also decreased expression of the Na+-K+-2Cl- cotransporter and the alpha-subunit of Na+-K+-ATPase compared with controls, whereas levels of the calcium-activated Cl- channel and CFTR were unaltered. Thus prolonged exposure to IFN-gamma leads to decreased ion secretion due, in part, to decreased ion transporter levels. These findings demonstrate the implications of elevated IFN-gamma levels in human small intestine and validate the human intestinal xenograft as a model to study chronic effects of physiologically relevant stimuli.     

Nitric oxide participates in the recovery of normal jejunal epithelial ion transport following exposure to the superantigen, Staphylococcus aureus enterotoxin B.

Bacterial superantigens (SAgs) are potent T cell activators. Mice treated 4 h previously with the SAg, Staphylococcus aureus enterotoxin B (SEB), display reduced ion transport (assessed by short circuit current) responses to prosecretory stimuli, which normalize 24 h posttreatment. Here, mice were treated with SEB alone or in combination with an inhibitor of the inducible form of NO synthase (iNOS), l -NIL. Subsequently, jejunal iNOS expression was detected by immunohistochemistry, ion transport was evaluated in Ussing chambers, and serum levels of TNF-alpha and IFN-gamma were measured by ELISA. SEB-treated mice had increased epithelial iNOS immunoreactivity, and numerous iNOS-positive CD3+ T cells occurred in their mucosa and submucosa. Concomitant treatment with l -NIL did not affect the reduced short circuit current responsiveness to electrical nerve stimulation or the prosecretory agents, carbachol and forskolin, that occurred 4 h post-SEB (5 microgram) treatment. However, Isc responses in l -NIL- plus SEB-treated mice were still significantly reduced 24 h posttreatment, indicating a role for NO in the restoration of normal ion transport following exposure to SAgs. The prolongation of epithelial ion transport abnormalities correlated with elevated serum levels of TNF-alpha and IFN-gamma in mice treated 24 h previously with l -NIL plus SEB compared with those in controls and SEB-only-treated mice. Additionally, mice treated with l -NIL plus SEB and TNF-alpha- or IFN-gamma-neutralizing Abs displayed normal jejunal ion transport characteristics 24 h posttreatment. We conclude that NO mobilization is important in the homeostatic recovery response following immune stimulation by SAgs and that the beneficial effect of NO in this model system is probably via regulation of TNF-alpha and IFN-gamma production.