Applicability of the Ussing chamber technique to permeability determinations in functionally distinct regions of the gastrointestinal tract in the rat

BACKGROUND: Ussing chambers are commonly utilized for in vitro investigations into gastrointestinal permeability. However, their sensitivity and applicability to the small intestine have not been well characterized. METHODS: In order to investigate the effects of experimentally induced damage and the relative contribution of the mucosa and muscularis externa layers to transmural permeability in the small intestine, stomach and colon, normal rat intestinal tissues were mounted in Ussing chambers with or without removal of the muscularis externa or mucosal layers. Gastric tissues were damaged in vivo by exposure to indomethacin (100 mg kg(-1)), while ileal tissues were damaged in vitro by 0.4 M NaCl. Tissue damage was assessed histologically, while permeability parameters included conductance (G), potential difference (PD) and mucosal to serosal flux of horseradish peroxidase (HRP). RESULTS: Damage localized to the tissue edges (edge damage) accounted for 25%-50% of the exposed epithelial length in the ileum, while less than 20% of stomach and colon epithelium was affected by edge damage. In the damaged stomach, a 20% reduction in epithelialization was accompanied by increases in G (P < 0.001) and HRP (P < 0.01) flux. Removal of the muscularis externa did not affect mucosal viability in the undamaged ileum or colon although HRP flux in the colon, but not ileum, was increased (P < 0.01). Removal of the ileal mucosa produced increases in G and HRP flux, while PD was maintained. CONCLUSION: We conclude that the Ussing chamber technique is suitable for application to studies of gastric and colonic permeability in rats. However, owing to the prevalence and extent of edge damage in the small intestine, we would caution against the use of this technique for permeability studies in this region of the gastrointestinal tract in the rat.     

Bidirectional assembly of tobacco mosaic virus in vitro

THE TIMING OF THE BIDIRECTIONAL GROWTH IN THE ASSEMBLY REACTION OF TOBACCO MOSAIC VIRUS HAS BEEN THE SUBJECT OF CONTROVERSY: Does elongation actually occur simultaneously to 5' and 3' ends or sequentially, first to the 5' end and then to the 3' end? To determine the timing of elongation toward the 3' end directly, using the S1 nuclease mapping method on a cloned cDNA with micrococcal nuclease-digested tobacco mosaic virus RNA, we analyzed encapsidation of the RNA region that was located downstream from the assembly origin. The results clearly showed that elongation toward the 3' end did not occur for at least the first 4 min. Actually it was first observed at 8 min. It is concluded that, in the first 5-7 min, a rapid elongation of the nucleation complex occurs only toward the 5' end of the RNA and that this gives rise to an intermediate particle 260 nm long. Furthermore, the lengths of the RNA that were protected against S1 nuclease digestion showed a clear banding pattern that had a spacing of approximately 100 nucleotides. This supports the hypothesis that the 20S aggregate is kinetically favored as the protein source for elongation to the 3' end.     

谷氨酰胺对体外培养肠上皮细胞屏障通透性的影响

目的:探讨谷氨酰胺保护肠黏膜屏障功能的作用机制.方法:Caco-2细胞(20-30代)应用含有不同浓度谷氨酰胺(0、0.1、1、4 mmol/L)的DMEM培养液在Transwell上培养21d,检测跨上皮电阻的变化.免疫荧光染色检测紧密连接蛋白occludin的定位、表达.应用不同裂解液制备NP-40可溶性及不溶性蛋白框架.分别进行蛋白印迹杂交检测活性和非活性occludin蛋白的相对含量.结果:与0mmol/L GLN组比较,补充GLN后,跨上皮电阻明显升高(21.4±0.1,124.5±0.3,173.6±0.2 vs 11.3±0.3,均P＜0.05).免疫荧光染色可见0mmmol/L GLN组occludin呈团状分布于细胞胞质内,随着GLN浓度的增加,occludin阳性荧光染色呈沿细胞膜分布的蜂巢状线性荧光.GLN缺乏不影响65kDa occludin蛋白的表达,但能降低85kDa occludin蛋白的表达(1.04±0.03,1.17±0.04,1.29±0.03,1.43±0.06,P＜0.05).结论:谷氨酰胺缺乏能够减少活性紧密连接蛋白occludin的表达,增加肠上皮细胞屏障通透性,补充GLN能够阻断这些改变.     

Effects of streptozotocin in vitro on proinsulin biosynthesis,insulin release and ATP content of isolated rat islets of Langerhans

Summary Proinsulin synthesis, insulin release and intracellular ATP concentrations were measured in isolated rat islets of Langerhans under control conditions of in vitro incubation and after treatment with several concentrations of streptozotocin for different periods of time. It was found that streptozotocin inhibited proinsulin synthesis, as well as insulin release, in a time and concentration dependent manner. The characteristics of the inhibition of these two processes were similar in general terms, but one dissimilarity was noted, i.e. after 60 min exposure to a high concentration of streptozotocin, proinsulin synthesis was inhibited more than insulin release. ATP content was reduced by high concentrations of streptozotocin, but it was found that proinsulin synthesis and insulin release could be inhibited without any effect on ATP content by a low (0.22 mM) concentration of streptozotocin. The effect of streptozotocin on proinsulin synthesis was judged to be the result of a target specificity for the B-cell rather than a specific effect on proinsulin relative to total protein synthesis.This work was supported by the Swiss National Scientific Foundation (Grant No. 3106073), Berne, Switzerland, and by a grant-in-aid from Hoechst Pharmaceuticals, Frankfurt-Hoechst, GermanyPreliminary data from this work were presented at the European Symposium on Hypoglycemia, Rome, April 5–6, 1974     

Glucose absorption in relation to ATP content of the small-intestine mucosa in the dog

Summary From an isolated small-intestine segment of the dog, isotonic glucose solution is better absorbed in vivo from the jejunum than from the ileum. At the same time, the ATP level of the mucosa of different GI tract areas does not vary significantly.Examining the relationship between circulation, glucose absorption and the mucosal ATP content of an isolated jejunal loop, we have ascertained that the decrease of blood supply to a certain limit does not influence the ATP level. A further reduction of the blood flow causes, however, a corresponding decrease of the ATP level. Between absorption of glucose and ATP content of the mucosa, a direct correlation is demonstrable.The possibility of a correlation between the ATP level and the absorption of sugar is discussed.     

Glucocorticoid receptor-mediated induction of glutamine synthetase in skeletal muscle cells in vitro

We studied the regulation by glucocorticoids of glutamine synthetase in L6 muscle cells in culture. Glutamine synthetase activity was strikingly enhanced by dexamethasone. The dexamethasone-mediated induction of glutamine synthetase activity was blocked by RU38486 [11 beta-(4-dimethylaminophenyl)17 beta-hydroxy-17 alpha-(prop-1-ynyl)estra-4,9-dien-3-one], a glucocorticoid antagonist, indicating the involvement of intracellular glucocorticoid receptors in the induction process. RU38486 alone was without effect. Northern blot analysis revealed that dexamethasone-mediated enhancement of glutamine synthetase activity involves increased levels of glutamine synthetase mRNA. Increased enzyme activity was specific for glucocorticoids; other steroid hormones were essentially without effect. The induction of glutamine synthetase was selective, in that glutaminase activity was not induced by dexamethasone treatment of L6 cells. Thus, glucocorticoids regulate the expression of glutamine synthetase mRNA in cultured muscle cells via interaction with intracellular receptors. Such regulation may be relevant to control of glutamine production by muscle.     

Relation of enzyme release and ATP content in digoxin-intoxicated guinea-pig hearts

Summary The isolated perfused, glycoside-intoxicated guinea-pig heart was used to investigate an eventual relation of myocardial ATP contents and drug-induced enzyme release. Digoxin in a concentration of 1.28 mol/l produced ventricular fibrillation and an extensive decrease of the myocardial ATP content, followed by the release of great activities of the cytosolic enzyme creatine kinase (CK).Normal control hearts, perfused for the same times (20 min; 1 h; 3 h), maintained their ATP contents, and released only small enzyme activities. When ventricular fibrillation was evoked electrically in control hearts, a considerable enzyme release and decrease of the myocardial ATP contents was obtained, too. These effects were, however, significantly smaller than in the glycoside-intoxicated hearts.A dissociation between the loss of ATP and the CK release in digoxin-intoxicated hearts was obtained with dexamethasone. Whereas the enzyme release was significantly decreased, the loss of ATP was not. The calcium antagonistic drug verapamil had no significant effects on ATP contents or CK release in the glycoside-intoxicated hearts.No support was obtained for the idea that the digoxin effects were mainly due to cardiac catecholamine liberation. -blocking agents (propranolol, practolol, metoprolol) had no antagonistic effects. And the catecholamine contents in digoxinintoxicated hearts were not different from those in control hearts.The findings are discussed in view of the assumption that retention and leakage of intracellular enzyme molecules are closely related to the energy metabolism of the myocardial cells.

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Zusammenfassung Am isoliert perfundierten, glykosidvergifteten Meerschweinchenherzen wurde geprüft, ob eine Beziehung zwischen der pharmakoninduzierten Enzymfreisetzung und dem myokardialen ATP-Gehalt besteht. Digoxin in einer Konzentration von 1,28 mol/l führte zu Kammerflimmern, starkem Abfall des ATP-Gehaltes und zur Freisetzung sehr großer Aktivitäten des Enzyms Kreatinkinase in die Perfusionsflüssigkeit. Bei normalen Kontrollherzen wurde bei gleicher Perfusionsdauer (20 min; 1 h; 3 h) nur eine geringe Enzymfreisetzung gefunden, und die myokardiale ATP-Konzentration wurde weitgehend aufrechterhalten. Wurde bei Kontrollherzen Kammerflimmern elektrisch ausgelöst, so kam es ebenfalls zu beträchtlicher Enzymfreisetzung und ATP-Schwund, die jedoch signifikant geringer waren als bei den glykosidvergifteten Herzen.Mit Dexamethason konnte die digoxinbedingte Enzymfreisetzung signifikant vermindert werden; der ATP-Schwund wurde jedoch nicht antagonisiert. Der Kalziumantagonist Verapamil beeinflußte die Enzymfreisetzung und die Abnahme des ATP-Gehaltes glykosidvergifteter Herzen nicht.Für eine wesentliche, ursächliche Beteiligung einer kardialen Katecholaminfreisetzung an den Digoxineffekten ergab sich kein Anhalt. -Blocker hatten keinen antagonistischen Effekt. Ferner unterschieden sich die Katecholamingehalte der glykosidvergifteten Herzen nicht von denjenigen normaler Kontrollherzen.Die Befunde werden im Hinblick auf die Annahme diskutiert, daß die Mechanismen der Retention und Freisetzung intrazellulärer Enzyme eng mit dem Energiestoffwechsel der Herzmuskelzellen verbunden sind.

     

Lack of enterocyte iron accumulation in the ferroportin disease

Ferroportin-associated iron overload (also known as the ferroportin disease) is a common cause of hereditary hyperferritinemia. It was originally proposed that loss-of-protein function mutations account for iron overload in the FD. This hypothesis is consistent with the phenotype reported in most patients with FD of early iron accumulation in tissues, particularly in macrophages, in spite of relatively normal-low circulatory iron. It was still unclear, however, how FPN mutations would affect iron retention in enterocytes. We studied histologically the intestine of six patients with different FPN mutations as compared to other subjects with various iron disorders. We found that regardless of the underlying FPN mutation, no iron accumulation was found in absorbing enterocytes while, intestinal villi showed marked signs of iron accumulation in the cells of lamina propria. Not surprisingly, in the liver, iron excess was found mainly in Kupffer cells. These results indicate that FPN haploinsufficiency is not limiting for iron export from enterocytes.     

谷氨酰胺对急性坏死型胰腺炎大鼠肠道衰竭的治疗作用

目的观察谷氨酰胺(Gln)对急性坏死型胰腺炎(ANP)大鼠肠道衰竭的治疗作用,并探讨其作用机制.方法 Spraque-Dawley 大鼠54只,随机分为假手术组(SO)、ANP组、Gln治疗组(ANP+Gln),每组18只.采用5%牛磺胆酸钠溶液经胆胰管内逆行注射诱导大鼠ANP模型.大鼠中心静脉置管,用微量输液泵输注含等氮、等热卡的氨基酸溶液,ANP+Gln组加入3%丙氨酸-Gln双肽(相当于2%Gln溶液,剂量0.5g·kg-1·d-1).术后24、48、72 h分批处死大鼠并留取标本,分别做肠黏膜组织病理检查,肝、胰、脾、肠系膜淋巴结(MLN)和腹水等组织细菌培养,门静脉血内毒素测定,TUNEL法检测肠黏膜上皮细胞凋亡;逆转录-聚合酶链反应研究肠黏膜组织胰岛素样生长因子1(IGF-1)、Gln酶和Gln合成酶mRNA表达.结果 SO组大鼠各组织培养均无阳性细菌,ANP组细菌培养阳性率明显高于SO组,P＜0.05,以MLN阳性率最高;ANP+Gln组细菌培养阳性率则显著低于ANP组,P＜0.05.血浆内毒素在ANP组明显高于SO组(P＜0.05),且随着时间延长而递升;ANP+Gln组血浆内毒素较ANP组显著下降(P＜0.05).ANP组肠黏膜绒毛高度显著低于SO组 (P＜0.05),提示ANP时肠黏膜处于萎缩状态,而ANP+Gln组较SO组则差异无显著性 (P＞0.05).ANP组肠黏膜上皮细胞凋亡指数明显高于SO组(P＜0.05),而ANP+Gln组较SO组差异无显著性(P＞0.05).SO组肠黏膜IGF-1、Gln酶和Gln合成酶 mRNA表达恒定,ANP组三者表达均明显下调,而Gln则能显著上调IGF-1、Gln酶和Gln合成酶 mRNA表达.结论 ANP大鼠肠黏膜屏障处于衰竭状态,并由此导致肠道细菌和内毒素移居.Gln可能通过刺激肠黏膜IGF-1、Gln酶和Gln合成酶 mRNA表达,下调肠黏膜细胞凋亡,从而促进肠黏膜修复,有效地控制ANP并发肠道衰竭.     

Bidirectional transfer and tissue accumulation of folic acid by rat intestine in vitro

The transfer and tissue content of 3H-pteroylmonoglutamate (PteGlu) from the mucosal to the serosal side (Jms, TCm) and in the reverse direction (Jsm, TCs) was studied using the everted sac technique. In the entire intestine, except for the colon, 3H-PteGlu was transferred preferentially into the serosal solution. When 3H-PteGlu was applied to the serosal side the final tissue concentration in either jejunal, duodenal, ileal or colonic segments was not significantly different from each other and about two-fold the serosal concentration. Apparently there exists a specific transfer process from the mucosal to the serosal side in the jejunum. The transfer of 3H-PteGlu shows saturation kinetics (S0.5 = 4.9 X 10(-5) mol/l). At low concentration (2 nmol/l) 3H-PteGlu was accumulated within the mucosal epithelium (tissue/mucosal fluid ratio = 3.8). Transfer and accumulation in the mucosal tissue of 3H-PteGlu apparently need high activation energy as indicated by the temperature dependency of these processes. Finally, transfer and accumulation in the tissue of 3H-PteGlu could be inhibited by salazosulfapyridine and phenobarbital.     

地塞米松与ATP联用在体外诱导细粒棘球绦虫原头节细胞凋亡的研究

目的 探讨地塞米松与三磷酸腺苷（ATP）联用在体外诱导细粒棘球绦虫原头节细胞凋亡的作用。 方法 体外培养细粒棘球绦虫原头节,分别设地塞米松（5 mmol/L）组、 ATP（1.6 mmol/L）组、 地塞米松（5 mmol/L）+ATP（1.6 mmol/L）组和空白对照组,显微镜下观察原头节变化。药物诱导8 h后,选取原头节形态改变最明显的一组和空白对照组,透射电镜观察这两组原头节的超微结构,原位末端脱氧核糖核苷酸转移酶标记技术（TUNEL法）检测原头节中的凋亡细胞,半胱氨酸天冬氨酸蛋白酶-3（caspase-3）活性检测试剂盒检测该酶活性,琼脂糖凝胶电泳检测两组原头节的DNA片段。 结果 药物诱导8 h后观察,与对照组相比,地塞米松组和地塞米松+ATP组的原头节均出现团缩、顶突内凹和体积缩小,钙颗粒明显减少且模糊不清,未见原头节活动,其中地塞米松+ATP组原头节的形态改变更明显,故选择该组作为实验组,与空白对照组进行后续试验。透射电镜观察见实验组原头节中实质细胞体积缩小、细胞膜皱缩、细胞基质浓缩、核异染色质凝集呈团块状或新月形边集于核膜下,表现出凋亡细胞的特征。TUNEL法在实验组的原头节中检测到散在的凋亡细胞,对照组则未见凋亡细胞。实验组caspase-3活性约为对照组的12倍。电泳结果显示,实验组DNA中有约150 bp的核小体DNA片段。 结论 地塞米松与ATP联用可在体外诱导细粒棘球绦虫原头节细胞凋亡。     

Alterations in carrier-mediated glutamine transport after a model of canine jejunal autotransplantation

The effects of small bowel transplantation (SBTx) on absorptive function are unknown. Preliminary experiments showed a decrease in absorption of glutamine. Our aim was to determine mechanisms of decreased ileal transport of glutamine utilizing a model of intestinal autotransplantation. Seven dogs were studied before and after a model of jejunoileal autotransplantation.In vivo absorption experiments were performed before and two and eight weeks postoperatively with an electrolyte solution containing glutamine (20 mM).In vitro glutamine transport was studied using brush-border membrane vesicles (BBMV) prepared from ileal mucosa obtained from six other dogs and compared to a controls.In vivo net absorptive flux of glutamine decreased at two weeks but returned toward baseline by eight weeks (P=0.06). Transport of glutamine into BBMVs was decreased at two weeks and remained decreased at eight weeks. , a measure of carrier affinity was unchanged but , a function of the number of transporter was decreased at two and eight weeks. Glucose transport was unchanged. It is concluded that jejunoileal autotransplantation decreases ileal absorption of glutamine by a decrease in carrier-mediated transport of glutamine.Supported in part by NIH DK39337 (M.G.S.), NIH CA45327 (W.W.S.), and the Mayo Foundation.Presented at the Society of Surgery of the Alimentary Tract, May 1995, in San Diego, California. An abstract of this work was published inGastroenterology 108:A1235, 1995.     

The protective effects of glutamine in a rat model of ventilator-induced lung injury

Background

The mortality rate of patients with acute respiratory distress syndrome (ARDS) is still high despite the use of protective ventilatory strategies. We sought to examine the pharmacological effects of glutamine (GLN) in a two-hit model of endotoxin-induced inflammation followed by ventilator-induced lung injury (VILI). We hypothesized that the administration of GLN ameliorates the VILI.

Methods

Sprague-Dawley rats were anesthetized and given lipopolysaccharide (LPS) intratracheally as a first hit to induce lung inflammation, followed 24 h later by a second hit of mechanical ventilation (MV) with either low tidal volume (6 mL/kg) with 5 cmH₂O of positive end-expiratory pressure (PEEP) or high tidal volume (22 mL/kg) with zero PEEP for 4 h. GLN or lactated Ringer’s solution as the placebo was administered intravenously 15 min prior to MV.

Results

In the LPS-challenged rats ventilated with high tidal volume, the treatment with GLN improved lung injury indices, lung mechanics and cytokine responses compared with the placebo group.

Conclusions

The administration of GLN given immediately prior to MV may be beneficial in the context of reducing VILI.     

Endoscopic biopsies in Ussing chambers evaluated for studies of macromolecular permeability in the human colon

OBJECTIVE: Studies of mucosal permeability to protein antigens in humans are limited to in vitro techniques. The use of surgical specimens for such studies has major shortcomings. Endoscopic biopsies in Ussing chambers have been introduced as a means of studying secretion and transepithelial permeability, but have not been evaluated for studies of protein antigen uptake in human intestine. MATERIAL AND METHODS: Standard forceps biopsies from the sigmoid colon of 24 healthy volunteers were mounted in Ussing chambers with an exposed tissue area of 1.76 mm2. 51Cr-EDTA (paracellular probe) and horseradish peroxidase (HRP; 45 kDa protein antigen) were used as permeability markers. Mucosal permeability, electrophysiology, histology and energy contents of the biopsies were studied over time. To evaluate the ability of the technique to detect permeability changes, the mucosa was modulated with capric acid, a medium-chain fatty acid, known to affect tight junctions. RESULTS: In the Ussing chamber the mucosal biopsies were viable for 160 min with stable levels of ATP and lactate, and only minor changes in morphology. Steady-state permeability with low variability was seen for both markers during the 30-90 min period. Exposure to capric acid induced a rapid decrease in short-circuit current (Isc) and a slower reversible decrease in transepithelial resistance (TER), as well as an increased permeability to 51Cr-EDTA and HRP. CONCLUSIONS: Endoscopic biopsies of human colon are viable in Ussing chambers and are reliable tools for studies of mucosal permeability to protein antigens. The technique offers a broad potential for studies of mucosal function in the pathophysiology of human gastrointestinal diseases.     

A novel method for mapping the heterogeneity in blood supply to normal and malignant tissues in the mouse dorsal window chamber

A novel first-pass imaging method for studying blood flow in tumors and normal tissues in mouse dorsal window chamber preparations is reported in this study. A fluorescence-labeled macromolecule is administered i.v. as a bolus dose, and the signal generated by the bolus is detected as the bolus passes through the vascular network. The sensitivity of the method is sufficiently high that the bolus can be detected in any tumor or normal tissue microvessel. The method is particularly useful for measuring the velocity and direction of blood flow in individual vessel segments of normal and malignant tissues and the blood supply time (BST) of individual tumor vessel segments; i.e., the time required for arterial blood to flow from a supplying tumor artery to a downstream microvessel segment. Since all vessels within a window chamber preparation can be studied simultaneously in a single imaging sequence, a significant benefit of the method is that it can be used to produce maps of velocity of blood flow and BST of the entire microvascular network of xenografted tumors.