Part I Inhibition of Gastric Acid Secretion Fat in the small bowel is a powerful inhibitor of gastric acid secretion. The gastric inhibitory agent(s) liberated from intestinal mucosa by the presence of fat has been named enterogastrone. Gastric inhibitory polypeptide (GIP), has been considered a candidate for enterogastrone. GIP is released into the circulation by infusion of fat into the proximal small bowel and inhibits gastric acid secretion under select experimental conditions. It has been proposed that the release of somatostatin, a potent inhibitor of acid secretion, may mediate the gastric inhibitory action of GIP. Recently, monoclonal antibodies raised to both GIP and somatostatin have been produced. The suitability of these antibodies for the study of the physiological roles proposed for their respective peptides is not known. This study examined the inhibitory action of GIP and somatostatin on gastric acid secretion in the rat and in man. GIP was found to be a weak inhibitor of meal-stimulated gastric acid secretion in man when given in supraphysiological doses. When administered at a dose which produces less than the normal maximal physiological plasma level, GIP had little effect on the acid secretory response to the meal and no effect on either plasma gastrin or plasma SLI concentrations. In the rat, infusion of GIP produced a 60% reduction of meal-stimulated acid secretion, independent of changes in serum gastrin release. Intraduodenal infusion of oleic acid in the rat reduced the gastric acid secretory response to a liver extract meal by 80% without affecting serum gastrin levels. A humoral gastric inhibitory agent, or "enterogastrone", was demonstrated in the portal blood of the rat following fat infusion. Intravenous infusion of portal serum, which had been collected during an intraduodenal infusion of fat, reduced meal-stimulated acid secretion in a second animal. A comparison of the inhibition of gastric acid secretion produced by intraduodenal infusion of either glucose or oleic acid with the release of IR-GIP in the portal serum was performed. The inhibitory effect of an intraduodenal fat infusion could not be explained by plasma IR-GIP. The release of GIP was not found to play a significant role in the mechanism for gastric inhibition by intestinal fat. Part II Monoclonal antibodies as Probes of Humoral Inhibitors of Gastric acid secretion The ability of recently produced monoclonal antibodies to block in vivo the inhibitory action of exogenous GIP and somatostatin on gastric acid secretion was examined. Anti-GIP monoclonal antibody demonstrated a high affinity for GIP when compared to the polyclonal rabbit antiserum R07 in the ELISA. When administered either as an intravenous bolus, or after incubation with GIP for 1 hour at 37°C, the antibody was unable to block the inhibitory effect of a GIP infusion on meal-stimulated gastric acid secretion in the rat. Monoclonal antibody 3.65H may not be suitable for the study of the role of endogenously released GIP. Two anti-somatostatin monoclonal antibody clones 58 and 510, when given as intravenous boluses, blocked the inhibitory action of exogenous somatostatin on meal-stimulated gastric acid secretion in the rat. The antibody clone S10 however, had no effect on the inhibitory action of exogenous GIP on gastric acid secretion. Although both monoclonal antibodies S8 and SIO effectively prevented the gastric inhibitory effect of infused somatostatin, the ability to block the physiological action of endogenously released gastric somatostatin remains to be determined. / Surgery, Department of / Medicine, Faculty of / Graduate

OBJECTIVE: Type 2 diabetes (T2D), the most common type of diabetes characterized by high blood glucose and insulin resistance, results from both genetic and environmental factors. Our lab has proposed that chronic excess nutrients induce insulin hypersecretion from the pancreatic ß-cell, contributing to hyperinsulinemia, a prequel to T2D. Normal glucose-stimulated insulin secretion (GSIS) is oscillatory, a feature that is lost in patients with T2D. In this thesis we examine the oscillatory secretion profiles of clonal pancreatic ß-cells cultured in normal and excess nutrients that mimic conditions of T2D. We also begin to examine oscillations in protein phosphorylation that may contribute to normal ß-cell metabolism and GSIS, but if altered might potentially lead to impaired insulin secretion. METHODS: Nutrient regulation of oscillatory insulin release was studied in clonal pancreatic β-cells (INS-1) cultured in multiwell plates in both low (4 mM) and high (11 mM) glucose. Insulin secretion was stimulated in cells from multiwell plates one well at a time at 30 sec intervals and sampled simultaneously at the end of the timecourse. Insulin secretion and insulin content were measured using a homogenous time-resolved fluorescence (HTRF) insulin kit (Cisbio). Protein was extracted from these same cells for analysis of time-dependent phosphorylation by western blot using specific antibodies. Protein phosphorylation was detected using SuperSignal West Femto chemiluminescence reagent (ThermoFisher) and imaged on an iBright Imaging System (Invitrogen). RESULTS: Insulin secretion from INS-1 cells grown in separate plates and in 4 mM glucose oscillated with a period of 8.2  0.5 min compared to 5.0  0.5 min in cells cultured at 11 mM glucose. The amplitude of oscillations was 40.4  11.5 and 14.6  1.5 for cells cultured in 4 and 11 mM glucose respectively. Oscillations in secretion from cells cultured in 4 and 11 mM glucose in the same plate were not different in period but different in amplitude due in part to reduced insulin content. Oscillation in the phosphorylation patterns of acetyl-CoA carboxylase (ACC) and myristoylated alanine rich C kinase substrate (MARCKS) were measured in cells cultured in 4 mM glucose and both exhibited a peak in phosphorylation that occurred at the nadir of the insulin oscillation between peaks of insulin release. CONCLUSION: Insulin secretion from pancreatic ß-cells is affected by nutrient status as excess nutrients decrease the amplitude of oscillations in insulin release. The period of oscillations can also be affected. Oscillations in protein phosphorylation are consistent with both ACC and MARCKS contributing to normal GSIS. These initial studies provide evidence of the suitability of this model system to correlate oscillations in protein activity to exocytosis. Future studies focused on the effects of low and high glucose will potentially reveal new important therapeutic targets that may help prevent/reverse/ameliorate insulin hypersecretion leading to insulin resistance and T2D.

No description available.

The airway epithelium plays a central role in respiratory physiology through its transport and immunological functions. Our previous study suggested that P2Y receptors are expressed in airway epithelia and play a significant role in regulating transepithelial ion transport. P2Y receptors belong to the family of purinergic receptors, which can be stimulated by nucleotides such as UTP and UDP. P2Y receptors are G protein-coupled receptors and classically signal through G[subscript q], resulting in an increase in intracellular Ca²⁺ concentration ([Ca²⁺]ᵢ) and thereby in the activation of Ca²⁺-dependent ion channels and downstream signalling pathway(s). Furthermore, P2Y receptors are involved in asthmatic inflammation. / Estrogen (or E₂) is an important hormone in human physiology. In addition to the classical nuclear hormone receptors ERα and ERβ, a novel estrogen receptor, G protein-coupled estrogen receptor (GPER), was recently identified and found to be involved in both rapid signalling and transcriptional regulations. The action of GPER is unclear, but it has been implicated in mediating anti-inflammatory responses. / In our experiments, both human bronchial epithelial cell line, 16HBE14o-, and primary normal human bronchial epithelial cells expressed GPER at mRNA and protein levels, as demonstrated by RT-PCR and western blotting, respectively. ERα and ERβ expression were also detected at mRNA and protein level. Expression of GPER receptors was localized in the human bronchial epithelial cells by immunofluorescence staining and western blotting of fractionated cell lysates. / [Ca²⁺]ᵢ induced by nucleotides were monitored by calcium imaging technique using MetaFluor fluorescence ratio imaging system. Stimulation of epithelial cells with E₂ or with the specific agonist of GPER, G1, rapidly attenuated a UDP-, UTP- or ATPyS- evoked increase in [Ca²⁺]ᵢ in both 16HBE14o- cell line and primary cells. This inhibitory effect of E₂ and G1 were concentration dependent, while this effect was reversed by GPER specific antagonist, G15. To examine the effect of E₂ and G1 on UDP-activated intracellular Ca²⁺ release and influx, the epithelia were exposed to nominally Ca²⁺ -free solution in the presence or absence of G1 or E₂, and then stimulated with UDP. Subsequently, Ca²⁺ was added to the perfusate. Both E₂ and G1 could inhibit UDP-induced Ca²⁺ release. However, only E₂ but not G1 could inhibit UDP-induced Ca²⁺ influx. / E₂ or G1 inhibited the secretion of two pro-inflammatory cytokines, interleukin (IL)-6 or IL-8, in cells stimulated by different nucleotides or the cationic protein, poly-L-arginie, as quantified by ELISA. CFP-Epac-YPF, an Epac-based polypeptide FRET reporter was used to monitor the real-time cAMP changes in 16HBE14o- cells. Both G1 and E₂ induced an increase in cAMP production. The transepithelial chloride (Cl⁻) secretion was measured using short circuit current technique in cells grown on permeable support. Cl⁻ secretion induced by apical UDP was partially inhibited by G1 in a concentration dependent manner. / Our results provide the first evidence that human bronchial epithelia express GPER, which interact with the P2Y receptor-mediated calcium signalling pathway and cytokine secretion. Moreover, the anti-inflammatory role of GPER may be due to its opposing effect on the pro-inflammatory pathway activated by the P2Y receptors in inflamed airway epithelia. / 气道上皮具有调节运输以及参与免疫反应等功能，在呼吸生理学研究中有着十分关键的意义。我们曾经的研究发现P2Y受体在气道上皮中表达并调节上皮细胞离子运输过程。P2Y受体属于嘌呤受体，可被三磷酸尿苷（UTP），二磷酸尿苷（UDP）等核苷酸激活。同时，P2Y受体也是一类G蛋白偶联受体，可通过活化G[subscript q]蛋白调控细胞内钙离子浓度而激活钙依赖性离子通道及其他下游信号通路。此外P2Y受体还参与哮喘炎症的调控。 / 雌激素（或雌二醇，E₂）是人体一类十分重要的激素。除传统的核受体ERα与ERβ外，一类新型雌激素受体GPER已被发现和鉴定。GPER属于G蛋白偶联受体，可同时参与转录调控和非基因依赖的快速信号调节。尽管具体机理尚不明确，但研究发现GPER可介导抗炎症反应。 / 实验结果显示，在支气管上皮细胞株16HBE14o-和原代人支气管上皮细胞中GPER都被检测到基因和蛋白水平的表达。GPER在人支气管上皮细胞中的定位也通过免疫荧光染色（immunofluorescence）和亚细胞组分蛋白质印迹（western blot of fractionated cells）得到鉴定。 / 本研究中，荧光显微技术（fluorescence microscopy）被用于测定核苷酸介导的细胞内钙离子浓度（[Ca²⁺]ᵢ）。在16HBE14o- 和原代培养人支气管上皮细胞中，E₂和GPER特异性激动剂G1都可抑制核苷酸介导的 [Ca²⁺]ᵢ增加，且这种抑制作用呈浓度依赖。GPER特异性拮抗剂G15可抵消G1的抑制作用。进一步研究表明，E₂和G1都可抑制UTP诱导的胞内钙库释放，然而只有E₂抑制UTP诱导的胞外钙离子内流。 / 除钙离子调节外，E₂和G1还可抑制支气管上皮细胞中核苷酸或聚精氨酸（poly-L-arginine）刺激介导的两种促炎症细胞因子，白介素6（IL-6）和白介素8（IL-8）的分泌。酶联免疫法（ELISA）被用于细胞因子的定量。同时，CFP-Epac-YPF作为一类多肽荧光共振能量转移（FRET）探针被转染入16HBE14o- ，探测细胞内腺苷-3',5'-环化一磷酸（cAMP）的实时变化。结果显示在人支气管上皮细胞中E₂和G1都可引导cAMP生成。此外，我们使用短路电流（short-circuit current, Isc）技术测定单层上皮细胞的氯离子（Cl⁻）分泌，并发现人支气管上皮顶膜面UDP诱导的Cl⁻ 分泌可被G1部分抑制，且抑制效果呈浓度依赖。 / 本研究首次证明GPER表达于人支气管上皮, 且激活GPER对P2Y受体介导的钙离子信号通路以及细胞因子生成起到抑制作用。这些结果表明在气道炎症反应中，GPER可通过反向调节P2Y受体激活的促炎症作用，达到抗炎症的效果。 / Hao, Yuan. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2014. / Includes bibliographical references (leaves 187-211). / Abstracts also in Chinese. / Title from PDF title page (viewed on 03, November, 2016). / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only.

No description available.

Secretion of appropriate amounts of insulin from pancreatic β-cells is crucial for glucose homeostasis. The β-cells release insulin in response to glucose and other nutrients, hormones and neurotransmitters, which trigger intracellular signaling cascades, that result in exocytotic fusion of insulin-containing vesicles with the plasma membrane. Increases of the intracellular concentration of calcium ions ([Ca2+]i) trigger exocytosis, whereas the messenger cyclic adenosine monophosphate (cAMP) amplifies various steps of the secretion process. The protein Epac2 mediates some effects of cAMP, but little is known about its regulation in β-cells. In this study, the spatio-temporal dynamics of Epac2 was investigated in insulin-secreting MIN6-cells and primary β-cells using various cell signaling biosensors and live-cell fluorescence microscopy approaches. Increases in the cAMP concentration triggered translocation of Epac2 from the cytoplasm to the plasma membrane. Oscillations of cAMP induced by glucose and the insulin-releasing hormone GLP-1 were associated with cyclic translocation of Epac2. Analyses of Epac2 mutants showed that the high-affinity cyclic nucleotide-binding domain and Ras-association domains were crucial for the translocation, whereas neither the DEP domain, nor the low-affinity cAMP-binding domain were required for membrane binding. However, the latter domain targeted Epac2 to insulin granules at the plasma membrane, which promoted their priming for exocytosis. Depolarization-induced elevations of [Ca2+]i also stimulated Epac2 translocation, but the effects were complex and in the presence of high cAMP concentrations, [Ca2+]i increases often reduced membrane binding. The stimulatory effect of Ca2+ was mediated by increased Ras activity, while the inhibitory effect reflected reduced concentrations of the membrane phospholipid PtdIns(4,5)P2. Anti-diabetic drugs of the sulfonylurea class, suggested to directly activate Epac2, induced translocation indirectly by depolarizing β-cells to increase [Ca2+]i. Epac2 is an activator of Rap GTPases, and its translocation increased Rap activity at the plasma membrane. It is concluded that the subcellular localization of Epac2 is controlled by a complex interplay between cAMP, Ca2+ and PtdIns(4,5)P2 and that the protein controls insulin release by binding to the exocytosis machinery. These results provide new insights into the regulation of β-cell function and may facilitate the development of new anti-diabetic drugs that amplify insulin secretion.

<p>Fluid secretion is essential to organ development and function, yet relatively little is known about the roles of fluid secretion <italic>in vivo</italic>. Early in development, fluid secretion plays important roles during the process of lumen formation and is necessary for organ homeostasis throughout life. A human disease, cystic fibrosis (CF) is caused by loss of cystic fibrosis transmembrane conductance regulator (CFTR) function, a chloride channel and key regulator of vertebrate fluid secretion. CFTR regulates fluid secretion by governing ion transport and osmotic gradients across epithelia. </p><p>To identify the developmental requirements for <italic>cftr</italic> function, we generated <italic>cftr</italic> mutant zebrafish using transcription activator like effector nucleases (TALENs). In <italic>cftr</italic> mutant zebrafish, we observed defects in the specification of left-right (LR) asymmetry. In the zebrafish, LR asymmetry is specified in part by directional fluid flow within a ciliated structure, Kupffer's vesicle (KV). Using live imaging of several transgenic markers in KV, we determined that lumen expansion is impaired in <italic>cftr</italic> mutants, which prevents directional fluid flow necessary for KV function. To examine <italic>cftr</italic> expression, we generated bacterial artificial chromosome (BAC) transgenic zebrafish expressing fluorescent Cftr fusion proteins under the control of the <italic>cftr</italic> promoter. These transgenes express Cftr within the KV epithelium and the protein localizes to the apical membrane. These transgenes rescue the KV function and the specification of LR asymmetry. These studies reveal a new role for <italic>cftr</italic> during KV morphogenesis and function in the zebrafish. </p><p>In the zebrafish pancreas, we found that loss of <italic>cftr</italic> function leads to defects reminiscent of CF including destruction of exocrine tissue and changes in islet morphology. Additionally, we observed exocrine pancreatic destruction by 3 weeks post fertilization (wpf). Analysis of <italic>cftr</italic> BAC expression in the adult and larval zebrafish pancreata revealed that <italic>cftr</italic> is expressed specifically within the ducts, localized to the apical membrane throughout life. Adult <italic>cftr</italic> mutant pancreata developed substantial degeneration of exocrine tissue and experienced reduced growth rates. In contrast, we found that <italic>cftr</italic> is not necessary for the specification or initial development of the larval pancreas. Exocrine and endocrine tissues developed similarly in WT and <italic>cftr</italic> mutant larvae. These results indicate that <italic>cftr</italic>-dependent fluid secretion is important for maintenance of the zebrafish pancreas. Altogether, these studies of <italic>cftr</italic> function in KV and the pancreas demonstrate that fluid secretion is an essential component of lumen morphogenesis and organ function.</p> / Dissertation

Thesis (MSc)--Stellenbosch University, 2004. / ENGLISH ABSTRACT: When in close contact with the Yellow Dog Tick, Haemaphysalis leachi, dogs show clear signs of disgust or even nausea. It is accepted that the secretion is produced by the tick in order to prevent the dog from removing the tick from its body with its teeth, thereby increasing the chances for the tick's survival. The composition of this secretion was studied in order to identify the chemical compounds responsible for the repellent action of the secretion. Because of the dog's keen sense of smell, the tick only needs to produce minute quantities of this repellant, which significantly complicated the detection of the different components by conventional GC-methods. Several sampling and sample enrichment methods were explored, including solvent extraction, SPME sample enrichment, adsorption on active charcoal, cryoprecipitation, sorption in a phasecoated open tubular trap, as well as solventless sampling, in order to determine which method would ensure an appropriate amount of sample for gas chromatographic detection. Two of these sampling methods yielded acceptable results: The first method consisted of rinsing irritated female ticks with dichloromethane and, after concentrating the sample by evaporation, GC-MS analysis using normal splitless injection. The second method entailed collecting secretions by wiping irritated ticks with glass micro fibre filter paper after which the paper was inserted directly into the inlet liner of the GCMS system, where thermal desorption of the volatile constituents of the secretion preceded gas chromatographic separation and mass spectral detection. Live dogs were needed for the evaluation of the isolated material to determine whether the samples had an aversive effect on them. The extract was separated into different fractions, which were further separated into subfractions. After each separation process, all the fractions were tested for efficacy in order to determine which fraction contained the active components, narrowing down the number of candidate target compounds. It was concluded that a combination of aldehydes, namely hexanal, heptanal, octanal, nonanal, decanal, undecanal and dodecanal, is responsible for the dog repelling action of the secretion. In most cases the semiochemicals of insects and mammals are secreted in a more complex matrix to ensure prolonged activity. For this reason some of the other compounds in the complex cuticular secretion of this tick species were also identified during the course of this study. / AFRIKAANSE OPSOMMING: Honde toon duidelike tekens van afkeer of selfs naarheid wanneer hulle in noue kontak kom met die afskeiding van 'n sekere bosluisspesie, die geelhondebosluis, Haemaphysalis leachi. Daar word aangeneem dat die bosluis die afskeiding produseer om te verhoed dat die hond dit met sy bek van sy liggaam verwyder. Hierdeur word die oorlewingskanse van die bosluis verbeter. 'n Studie is gemaak van die samestelling van die vlugtige komponente van hierdie afskeiding om die chemiese verbindings, wat verantwoordelik is vir die afweer van honde, te identifiseer. As gevolg van die sensitiwiteit van 'n hond se reuksintuig, is dit vir die bosluis nodig om slegs uiters klein kwantiteite van hierdie afweerstof af te skei, wat die waarneming van die verskillende komponente deur middel van konvensionele GC-metodes baie bemoeilik het. Ten einde die mees effektiewe metode te vind wat 'n gepaste hoeveelheid monster vir waarneming op 'n gaschromatograafdetektor sou verseker, is verskeie monsternemings en -verrykingsmetodes ondersoek, naamlik oplosmiddelekstraksie, SPME-monsterverrykingsmetodes, adsorpsie op aktiewe koolstof, kriopresipitasie, sorpsie in 'n fase-belaagde oopbuisval en oplosmiddellose monsterneming, Twee monsternemingsmetodes het aanvaarbare resultate gelewer: Met die eerste metode is geïrriteerde wyfiebosluise met dichlorometaan afgespoel en die ekstrak is na indamping met behulp van monsterinspuiting sonder inlaatstroomverdeling deur middel van GC-MS geanaliseer. Met die tweede metode is die afskeiding van geïrriteerde bosluise met mikroglasveselpapier afgevee en die papier is direk in die binnebuis van die inlaat van die GC-MS-sisteem geplaas, waar die vlugtige komponente termies gedesorbeer is vir gaschromatografiese skeiding en massaspektrometriese waarneming. Om die aktiwiteit van die geïsoleerde materiaal te evalueer, is van lewende honde gebruik gemaak, om vas te stel of hulle aversie teenoor die betrokke monsters toon. Die ekstrak is in verskillende fraksies geskei, wat weer in subfraksies verder geskei is. Alle fraksies is na elke skeidingsproses getoets vir effektiwiteit om vas te stel watter van die fraksies die aktiewe verbindings bevat. Sodoende is die aantal moontlikhede vir die teikenverbindings met elke skeidingstap verminder. Daar is gevind dat 'n reeks aldehiede, naamlik heksanaal, heptanaal, oktanaal, dekanaal, undekanaal en dodekanaal, gesamentlik verantwoordelik is vir die afweer van honde. Insekte en soogdiere skei dikwels semioverbindings in 'n draermateriaal af om daardeur meer langdurige werking te verseker. In hierdie ondersoek is dus ook 'n begin gemaak met die identifisering van die ander verbindings wat in die besonder komplekse kutikulêre afskeiding van hierdie bosluisspesie aanwesig is.

published_or_final_version / Physiology / Doctoral / Doctor of Philosophy

Female mosquitoes of the species, Aedes aegypti (yellow fever mosquito, Diptera), blood feed for oogenesis. Therefore, mosquitoes are exposed to high iron loads and possibly blood-borne pathogens. We are interested in studying iron metabolism in A. aegypti to find methods for controlling mosquito populations, and thereby reduce human exposure to these pathogens. First, we found that the expression of the Aedes ferritin light chain homologue (LCH) is up-regulated by blood feeding. Ferritin LCH and heavy chain homologue (HCH) genes are closely clustered together and both mRNA transcripts increase with iron and oxidative stress (H2O2 and hemin). Second, we show A. aegypti larval cells synthesize and secrete ferritin in response to iron. Cytoplasmic ferritin is maximal at low levels of iron, consists of a specific subunit composition and reflects cytoplasmic iron levels. Secreted ferritin increases in linear relationship to increasing iron dose and is composed of different subunits than cytoplasmic ferritin. HCH and LCH transcripts increase with increasing cytoplasmic iron suggesting transcriptional control of ferritin synthesis. We previously reported that the mosquito HCH mRNA has an iron responsive element (IRE), but LCH mRNA does not have a canonical IRE. We show that iron regulatory protein 1 (IRP1)/IRE binding activity declines in response to increasing cytoplasmic iron levels. These data would indicate that HCH synthesis is controlled at transcription and translation. Third, we report that A. aegypti larval cell cytoplasmic iron concentration does not change temporally with iron treatment. However, membrane iron levels increase with iron over time. Iron temporally up-regulates both HCH and LCH mRNA. Ferritin secretion increases with time in response to iron and reflects that most of the intracellular ferritin is found in the membrane fraction. Membrane ferritin has the same subunit composition as cytoplasmic ferritin. Finally, membrane ferritin is found in both non-iron and iron-treated cells. This suggests a mechanism to store iron from a blood meal in membrane ferritin. These results indicate Aedes ferritin could act as an antioxidant and holoferritin secretion is likely the mechanism whereby mosquito cells protect against iron overload and, thus reduce the intracellular potential for iron-mediated oxidative stress during blood feeding.