Biomedical subjects

A W Baird

Publications and source records attributed to A W Baird.

At least 37 records · Page 2Linked to original sources

PubMed1998

Concanavalin A-stimulated proliferation of T cell subset-depleted lymphocyte populations isolated from Fasciola hepatica-infected cattle.

Over 14 weeks, peripheral blood lymphocytes (PBL) were isolated from eight adult cattle which had been orally infected with Fasciola hepatica via trickle infection over a 10-day period. Two age, breed and sex-matched cattle served as controls. CD4+, CD8+ and gammadelta+ T cells were depleted from whole PBL populations by magnetic bead depletion. Lymphocyte proliferation assays demonstrated a transient, but marked elevation in responsiveness to Concanavalin A (Con A) between weeks 2 and 4 post-infection in PBL from infected animals. Proliferative responses to Con A were significantly greater in PBL from infected cattle than uninfected/control cattle over the initial period of the experiment. Con A-stimulated proliferation of PBL isolated from infected cattle followed a similar pattern to PBL responses to F. hepatica antigen. In both whole and subset-depleted lymphocyte populations from infected cattle, proliferative responses to Con A decreased from day 28 post-infection. Depletion of CD4+, CD8+ and gammadelta+ T cell subpopulations significantly augmented responses soon after infection. These findings suggest that the capacity of bovine PBL to proliferate in response to Con A stimulation, was in some way attenuated by F. hepatica infection and proliferative responses due to non-specific activation was suppressed by the coordinated activities of various lymphocyte subsets.

Animals↗

PubMed1998

Local immune responses in colon from cattle infected with Fasciola hepatica.

Colonic mucosae isolated from eight Charolais heifers 14 weeks after oral infection with Fasciola hepatica metacercariae were voltage clamped in Ussing chambers. Antigen challenge provoked a rapid-onset, inward short circuit current in infected but not in control tissue preparations. Chloride secretion accounted for part of the response as the loop diuretic bumetanide attenuated the response to antigen by 89%. The bacterial cell wall component n-formyl-methionyl-leucyl-phenylalanine induced a similar response to antigen and partly desensitised tissues to subsequent antigen challenge, consistent with the involvement of immunocytes in the response to antigen. Infection induced an elevation in the number of tissue eosinophils compared with control colon.

Animals↗

PubMed1998

Helicobacter pylori disrupts epithelial barrier function in a process inhibited by protein kinase C activators.

Helicobacter pylori colonizes the gastric mucosa, and the infection is related to the development of diverse gastric pathologies, possibly by directly or indirectly affecting epithelial-cell function. We analyzed the influence of the bacteria on transepithelial electrical resistance (TER) on a model tight epithelium, T84, grown to confluence in permeable filters. H. pylori sonicates produced a dramatic decrease in TER after 1 to 2 h of exposure, while sonicates from other bacteria did not induce a significant reduction of TER. The effect induced by sonicates was mimicked by a water-soluble fraction from the bacterial surface, was not reproducible with isolated lipopolysaccharide, and was concomitant with a significant increase in the paracellular permeability of the marker molecule [14C]mannitol. Furthermore, H. pylori sonicates also provoked a significant increase in permeability to [14C]mannitol across rat gastric mucosa in vitro. The sonicate-induced decrease in TER in T84 monolayers was inhibited by the protein kinase C (PKC) activator phorbol myristate acetate. As PKC is directly involved in tight junction regulation, we suggest that H. pylori may induce intracellular signalling events counteracting PKC effects. Following long-term H. pylori stimulation, epithelial monolayers regained baseline resistance values slowly after 24 h. The resistance recovery process was inhibited by cycloheximide, indicating its dependency upon protein synthesis. No association between resistance variation and E-cadherin protein levels was observed. These results indicate that H. pylori alters in vitro the barrier properties of the epithelium, probably by generating cell signalling events counteracting the normal function of PKC. This increased permeability may provide a potential mechanism by which H. pylori antigens can reach the gastric lamina propria, thereby activating the mucosal immune system.

Animals↗

PubMed1997

Complement activation of electrogenic ion transport in isolated rat colon.

The complement cascade is an important component in many immune and inflammatory reactions and may contribute to both the diarrhoea and inflammation associated with inflammatory bowel disease. Isolated rat colonic mucosae were voltage clamped in Ussing chambers. Basolateral addition of zymosan-activated whole human serum (ZAS) induced a rapid onset, transient inward short circuit current (SCC). This response was concentration dependent and was significantly attenuated by pre-heating ZAS at 60 degrees C for 30 min. Depletion of complement from normal human serum with cobra venom factor (CVF) significantly lowered SCC responses. Chloride was the primary charge carrying ion as responses to ZAS were abolished in the presence of the loop diuretic bumetanide. The complement component C3a stimulated ion transport but not to the same extent as whole serum. Exogenous C5 was without effect. The cyclooxygenase inhibitor piroxicam significantly attenuated the response to ZAS. These findings support the possibility that complement activation may contribute to the pathophysiology of secretory diarrhoea since activation of electrogenic chloride secretion converts intestinal epithelia to a state of net fluid secretion.

Animals↗

PubMed1997

Changes in barrier function of a model intestinal epithelium by intraepithelial lymphocytes require new protein synthesis by epithelial cells.

BACKGROUND: Elements of the mucosal immune system may play an important part in regulating epithelial barrier function in the intestinal tract. Intraepithelial lymphocytes (IELs) represent a subtype of immunocyte which is strategically placed to regulate epithelial function at most mucosal sites. AIMS AND METHODS: An IEL derived cell line (SC1) was used to examine its effects on the model epithelium T84--a tumour derived cell line which retains the phenotype of colonic crypt cells. Transepithelial electrical resistance (TER) was used as a marker of epithelial integrity. RESULTS: Coculture of T84 cells with SC1 produced a significant fall in TER as did exposure of T84 monolayers to IEL derived supernatant. Recombinant interferon-gamma (rIFN gamma) also reduced TER in T84 monolayers. Cycloheximide prevented the effects of IEL supernatant and of rIFN gamma on TER. The fall in TER in response to rIFN gamma was attenuated by blocking antibodies, which did not alter the fall in resistance induced by IEL supernatant. Fractions of IEL supernatant, separated on the basis of size, evoked temporally distinct changes in TER. Ultrastructural studies support the hypothesis that the slow onset but severe fall in TER indicates catastrophic effects on the monolayer. The more rapid onset fall in TER was not associated with gross changes in monolayer morphology. Reduction of TER by IEL supernatant was not influenced by inhibitors of tyrosine phosphatase or of protein kinase C. Although herbimycin did reduce the rapid onset change in TER, the tyrosine kinase inhibitor genistein did not alter responses to IEL supernatant. CONCLUSIONS: Mucosal T cells may influence barrier function by a process involving new protein synthesis by epithelial cells. This model may have relevance in some inflammatory conditions of the gastrointestinal tract.

Benzoquinones↗

PubMed1995

Regulation of ion transport by histamine in human colon.

Histamine, added to the basolateral side of voltage clamped human colon in vitro, induced a rapid onset, transient inward short circuit current which was concentration dependent over the range 0.01-3 mM. This response was largely due to electrogenic chloride section since it was virtually abolished by bumetanide or by chloride replacement in the bathing solutions. Responses were unaffected by amiloride or acetazolamide. Neither the histamine H2 receptor agonist dimaprit (1 mM) nor the histamine H3 receptor agonist S-(+)-alpha-methyl histamine (1 mM) altered short circuit current. Responses to histamine were significantly reduced by the histamine H1 receptor antagonist mepyramine (1-10 microM) but not altered by the histamine H2 receptor antagonist cimetidine (100 microM) or by the histamine H3 receptor antagonist thioperamide (1 microM). Short circuit current responses to histamine were not altered by tetrodotoxin (1 microM). Piroxicam (10 microM) and nordihydroguaiaretic acid (100 microM) were without effect when used individually but significantly reduced responses to histamine when used simultaneously. These results indicate that histamine stimulates chloride secretion across human colonic epithelium by a mechanism which is mediated exclusively via histamine H1 receptors. This action does not involve intrinsic nerves but appears to be dependent upon eicosanoid synthesis.

Arachidonic Acid↗

PubMed1995

Cholinergic activation of Cl- secretion in rat colonic epithelia.

Acetylcholine receptor agonists and antagonists were used in a pharmacological analysis to identify which muscarinic receptor(s) may be involved in cholinergic regulation of Cl- secretion across rat colonic mucosa in vitro. A comparative ligand binding analysis for each of the antagonists was carried out in parallel. Both studies elicited identical rank order potencies (atropine > or = 4-diphenyl-acetoxy-N-piperidine methiodide (4-DAMP) > pirenzepine > 11-[[2[(diethylamino)methyl]-1-pipiridinyl]acetyl[5,11- dihydro-6H-pyrido[2,3-b]]1,4]benzodiazepine-6-one (AF-DX 116). Cholinomimetic-induced Cl- secretion was predominantly mediated by activation of muscarinic receptors in rat isolated colonic mucosa, with only a modest contribution from nicotinic receptors. Short circuit current responses evoked by the selective muscarinic M1 receptor agonist 4-[[(3-chlorophenyl)amino]carbonyl]-N,N,N-trimethyl-2-butyn-1-a minium chloride (McN-A-343) suggest that this receptor subtype, which is thought to be neuronally sited, also plays a minor role in regulation of intestinal ion transport. The principal epithelial cell receptors responsible for acetylcholine receptor-mediated Cl- secretion appear to belong to the M3 class.

(4-(m-Chlorophenylcarbamoyloxy)-2-butynyl)trimethy↗

PubMed1995

Berberine inhibition of electrogenic ion transport in rat colon.

1. The effects of the alkaloid berberine on basal and stimulated ion transport were investigated in voltage-clamped rat colonic epithelia. 2. Berberine (100-500 microM) reduced basal short circuit current (SCC) when applied basolaterally but not when applied apically. 3. SCC responses to mast cell activation by anti-rat IgE were significantly attenuated in the presence of berberine. 4. Berberine, applied to the basolateral bathing solution, also reduced SCC responses to the following agents which stimulate chloride secretion in rat colon: carbachol, forskolin, sodium nitroprusside, dibutyryl cyclic-AMP, heat-stable E. coli enterotoxin, 8-bromo-cyclic GMP and thapsigargin. Calcium mediated ion transport responses appear to be more sensitive to berberine inhibition than those which are cyclic GMP-mediated, which in turn are more sensitive than cyclic AMP-mediated responses. 5. Berberine added apically was without effect upon forskolin-stimulated ion transport. Cytochalasin D treatment of the lumenal surface of rat colon conferred apical-side sensitivity to berberine. 6. Berberine (at concentrations up to 500 microM) was without effect on generation of cyclic AMP by forskolin or on generation of cyclic GMP by sodium nitroprusside in isolated mucosal segments. Protein kinase A activity stimulated by dibutyryl cyclic AMP was unaffected by berberine (at concentrations up to 500 microM). 7. The precise mechanism of action of berberine remains to be elucidated. However, its site of action appears to be distal to second messenger production and may be at a level common to all stimuli of colonic chloride secretion.

8-Bromo Cyclic Adenosine Monophosphate↗

PubMed1995

Immune regulation of human colonic electrolyte transport in vitro.

The role of lamina propria cells in regulating human colonic ion transport was investigated in vitro. Normal human colonic mucosae were mounted in Ussing chambers, and short circuit current changes (delta SCC) were monitored in response to immune cell activation. Anti-human immunoglobulin E (anti-IgE) and formyl-Methionyl-Leucyl-Phenylalanine (fMLP) were used to stimulate mast cells and phagocytes respectively. Anti-IgE (100 micrograms/ml) and fMLP (100 microM) evoked rapid onset, inward delta SCC (mean (SEM) max delta SCC 19.3 (2.8) and 29.4 (4.7) microA/0.63 cm2 respectively). A pharmacological approach was used to identify the charge carrying ion species and to characterise mediators involved in the SCC response. Responses to each secretagogue were significantly attenuated by bumetanide, indicating that the delta SCC was at least partly due to electrogenic chloride secretion. Piroxicam reduced the delta SCC to mast cell and phagocyte activation by 91.1 (3.4)% and 48.2 (25.2)% respectively, implicating eicosanoids as mediators of the responses. Mepyramine (100 microM) reduced the SCC responses to anti-IgE by 79.6 (12.0)% but did not significantly alter delta SCC responses to fMLP. Desensitisation to repeated anti-IgE or fMLP stimulation, and cross desensitisation between each of the stimuli, were features of immune cell activation. In summary, we have shown that activation of immune cells can stimulate electrogenic chloride secretion. Such events in vivo will result in gradient driven secretory diarrhoea, which may occur as a protective response to enteric-dwelling parasites, or as a feature of local bowel inflammation.

Antibodies, Anti-Idiotypic↗

PubMed1994

Regulation of chloride secretion in mammalian colon.

A number of procedures or interventions which activate electrogenic ion transport in mammalian intestine are reviewed. Using in vitro models it is possible to demonstrate direct or indirect pathways to stimulate chloride secretion. Such activation, in vivo, would change the gut from a state of net water absorption to one of fluid secretion. The movement of water is driven by electrical and osmotic gradients set up as a consequence of opening regulated ion channels in epithelial cells. Secretagogues may govern epithelial intracellular second messenger pathways to regulate ion channel activity directly or by activation of membrane bound receptors on the surface of epithelial cells. In health or disease secretagogues may be derived from cells within the attendant lamina propria of the intestinal mucosa. Pharmacological techniques may be employed to determine which mediators contribute to indirect stimulation of electrogenic ion transport by activation of neurons or of immunocytes (mast cells or phagocytes). Dissection and reconstruction of models of intestinal hypersensitivity reactions show that neuro-immune networks which regulate intestinal ion transport appear to be complex, functionally integrated systems. Analysis of such interactions may identify cellular or humoral targets with which to examine novel diagnostic, preventative or therapeutic strategies with regard to intestinal diseases.

Animals↗

PubMed1994

A distinctive electrophysiological signature from the Peyer's patches of rabbit intestine.

1. Rabbit small intestinal segments containing Peyer's patches (PP) were examined in Ussing chambers using short-circuit current (Isc) recording. By comparison with control small intestinal mucosal segments, rabbit PP-containing epithelia exhibited decreased basal Isc, increased transepithelial resistance (TER) and unchanged potential difference (PD). 2. Carbachol caused a decrease in Isc in rabbit PP epithelia. Forskolin, dibutyryl cyclic GMP, histamine and the calcium ionophore, A23187, were without effect. In contrast, control epithelial segments of rabbit intestine responded to carbachol and forskolin with an increased Isc, indicative of electrogenic chloride secretion. The EC50 for carbachol was approximately 2 microM in both types of epithelia. Methacholine also caused an outward current in rabbit PP epithelia which had similar properties to that of carbachol. The effect of the cholinomimetics on rabbit PP was basolateral-sided, reversible, and sensitive to low concentrations of the general muscarinic cholinoceptor blockers, atropine, scopolamine and also to the M1 cholinoceptor blocker, pirenzepine. 3. The Isc response to cholinomimetics in rabbit PP was insensitive to bumetanide, amiloride, TEA, barium, acetazolamide, piroxicam and omeprazole, but was attenuated in the presence of ouabain. Using bilaterally-substituted solutions, the carbachol effect on rabbit PP Isc was abolished in chloride/bicarbonate-free, but not in chloride-free solutions, suggestive of stimulation of electrogenic bicarbonate absorption by the agent. Substitution for sodium abolished both the basal current and the Isc response to carbachol. Part of the effect of carbachol on PP Isc appeared to be mediated by submucosal neurones because addition of tetrodotoxin reduced the effect by 60%. 4 As microfold (M) epithelial cells predominate in the PP of the rabbit, the unusual phenotype of cholinomimetic-induced outward current may be used as an electrophysiological marker for these potential sites of oral vaccine delivery, and in particular it may also be of use as a marker for rabbit M cells.

Animals↗

PubMed1993

Epithelial ion transport - possible contribution to parasite expulsion.

Multiple local effector mechanisms contribute to host protection from multicellular parasites. In this article, Alan Baird and Kate O'Malley describe a technique for voltage clamping isolated intestinal mucosae obtained from previously parasitized animals. Antigen challenge evoked an ion transport response which is the mechanism underlying net fluid secretion that may contribute to repulsion of enteric-dwelling parasites.

Journal Article↗

PubMed1993

Type I hypersensitivity reactions in intestinal mucosae from rats infected with Fasciola hepatica.

Type I hypersensitivity reactions in the intestinal tract of sensitized animals may contribute to resistance to reinfection with Fasciola hepatica. Colonic mucosae isolated from previously infected rats were voltage clamped in Ussing chambers. Antigen was prepared as a crude homogenate from adult liver fluke. Assay of serum antibodies against fluke antigen confirmed sensitization. Antigen challenge evoked a rapid onset, transient inward current in sensitized but not in control preparations. Chloride secretion accounted for at least part of the response since the loop diuretic bumetanide reduced the effect of antigen by 61%. Anti-rat IgE mimicked the response to antigen and desensitized tissues to subsequent antigen challenge. Local synthesis of eicosanoids may mediate the response to antigen since the cyclo-oxygenase inhibitor piroxicam reduced the response by 76%. In contrast, mepyramine which is a histamine receptor antagonist did not alter the ion transport response evoked by antigen. Tetrodotoxin reduced the response to antigen by 53% implicating intrinsic neurons within the lamina propria as effector cells in the responses of this tissue to antigen. We propose that antigen stimulation of electrogenic chloride movement and consequent fluid secretion in vivo may contribute to a local effector mechanism in prevention of reinfection of previously sensitized hosts.

Acetylcholine↗

PubMed1992

Increased sensitivity of guinea pig gallbladder in vitro to bradykinin.

Bradykinin evoked concentration dependent contractions of guinea pig gallbladder smooth muscle strips in vitro. Responses to kinins increase over three hours of incubation. Induction of a B1-mediated action, waning activity of endogenous kininase(s) and involvement of eicosanoids as mediators have been investigated as potential contributing mechanisms to the four-fold, time dependent increase in response of this tissue to bradykinin.

Animals↗

PubMed1992

Regulation of bradykinin-induced chloride secretion in a human epithelial cell line.

The chloride secretory response to bradykinin in T84 cells is regulated. The efflux rate of 125I from these cells can be used to measure this response, and to demonstrate that the sensitivity to bradykinin varies with time in culture. The response in NuT84 cells is greater than that in T84, and can be blocked by the B2 receptor antagonist HOE-140.

Bradykinin↗

PubMed1991

Enhancement of kallikrein production and kinin sensitivity in T84 cells by growth in the nude mouse.

The production of tissue kallikrein and the short-circuit current (SCC) response in the human colonic epithelial cell line T84 to bradykinin have been studied. These cells produce true tissue kallikrein and secrete it into the growth medium, and addition of bradykinin results in a small increase in SCC. After growth of T84 cells as a xenograft in athymic (nude) mice (NuT84), however, the cellular concentration of the enzyme increases 38-fold, and the maximal change in SCC (delta SCC) induced by bradykinin increases 35-fold. The SCC response to prostaglandin E1 is not changed, and the response to forskolin increases eightfold. The bradykinin-induced delta SCC was inhibited by piretanide, suggesting that a secretory movement of chloride was responsible for the change, and the effect was attenuated by an antagonist to kinin receptors. We conclude that both the production of true tissue kallikrein and the chloride secretory response to bradykinin can be regulated in T84 cells by changes in the cell environment.

Animals↗

PubMed1989

Bradykinin stimulates electrogenic bicarbonate secretion by the guinea pig gallbladder.

We studied bradykinin effects upon electrogenic ion transport across voltage-clamped guinea pig gallbladder, and found stimulation after both mucosal (EC50 = 0.2 microM) and serosal addition (EC50 = 10 microM). The mucosal effect is dose-dependent, reproducible and sustained. Responses to bradykinin were unaffected by amiloride (1 mM) or piretanide (1 mM) but were attenuated by acetazolamide (1 mM), indicating the charge-carrying ion species to be bicarbonate. This was confirmed by abolishing the short circuit current response to bradykinin with bicarbonate-free solutions. Tetrodotoxin (1 microM) did not alter the response, indicating that neurons are not involved. This effect of bradykinin on gallbladder bicarbonate transport appears to be dependent upon arachidonate metabolism because the cyclooxygenase inhibitor piroxicam reversibly abolished the effect. In addition, prostaglandin E2 was more effective (EC50 = 0.01 microM) than bradykinin in stimulating short circuit current. This newly appreciated ion transporting effect of bradykinin occurs in a tissue where kinin effects upon afferent nerve endings and smooth muscle are also evident and raise several questions about kinin involvement in stone formation or local inflammatory events.

Acetazolamide↗

PubMed1988

Intestinal anaphylaxis: rapid changes in mucosal ion transport and morphology.

Anaphylactic reactions can be elicited by beta-lactoglobulin (beta LG) in the isolated colonic and ileal mucosae of guinea pigs fed cow milk. We have shown that these tissues respond to antigen challenge with a rapid rise in short-circuit current (SCC) due to net chloride secretion in the colon and less well-characterized ion movements in the ileum. Here, tissues were characterized morphologically at or near the peak of the SCC response 2 min after antigen addition. These sensitized preparations, or naive tissues passively sensitized with immune sera and challenged with beta LG, showed numerous structural alterations that correlated significantly with the change in SCC. In the ileum, these changes included compound exocytosis of mucous granules from goblet cells of crypts but not of villi and a decrease in the intercellular space of the crypts. In contrast, colonic goblet cells of both crypts and luminal surface showed no evidence of secretion, but crypt architecture was reproducibly and characteristically altered. Thus antigen challenge of intestinal mucosa results in temporally related but diverse changes in morphology and ion transport.

Anaphylaxis↗