Water channel protein AQP3 is present in epithelia exposed to the environment of possible water loss.

Aquaporins (AQPs) are membrane water channel proteins expressed in various tissues in the body. We surveyed the immunolocalization of AQP3, an isoform of the AQP family, in rat epithelial tissues. AQP3 was localized to many epithelial cells in the urinary, digestive, and respiratory tracts and in the skin. In the urinary tract, AQP3 was present at transitional epithelia. In the digestive tract, abundant AQP3 was found in the stratified epithelia in the upper part, from the oral cavity to the forestomach, and in the simple and stratified epithelia in the lower part, from the distal colon to the anal canal. In the respiratory tract, AQP3 was present in the pseudostratified ciliated epithelia from the nasal cavity to the intrapulmonary bronchi. In the skin, AQP3 was present in the epidermis. Interestingly, AQP3 was present at the basal aspects of the epithelia: in the basolateral membranes in the simple epithelia and in the multilayered epithelia at plasma membranes of the basal to intermediate cells. During development of the skin, AQP3 expression commenced late in fetal life. Because these AQP3-positive epithelia have a common feature, i.e., they are exposed to an environment of possible water loss, we propose that AQP3 could serve as a water channel to provide these epithelial cells with water from the subepithelial side to protect them against dehydration. (J Histochem Cytochem 47:1275-1286, 1999)     

Expression of aquaporin-4 water channels in the digestive tract of the guinea pig

Expression of the aquaporin-4 (AQP4) water channel was systematically studied in the digestive tract of the guinea pig using Western blot and immunofluorescence techniques. The results showed that AQP4 was expressed widely in different segments of the guinea pig digestive tract. AQP4-immunoreactivity was confined to parietal cells in the stomach, and absorptive and glandular epithelial cells of small and large intestine. AQP4 protein was also expressed by enteric glial cells of submucosal and myenteric ganglia and primary nerve trunks. AQP4 was expressed by both type I and type II enteric gliocytes, but not by type III or type IV enteric gliocytes, indicating that enteric gliocytes have a heterogeneous distribution in the gut wall. In addition, different patterns of AQP4 expression in the enteric nervous system of human, guinea pig, rat and mouse colon mucosa were identified: in rat and mouse AQP4 was localised to a small subpopulation of neurons; in the guinea pig AQP4 was localised to enteric glial cells; and in the human colon mucosa, AQP4 was also detected mainly in the glial cells. It has been speculated that AQP4 may be involved in water transport in the gastrointestinal tract. Its role in enteric neurons and glia is unknown, but, by analogy with the brain, AQP4 may be involved in the formation and resolution of edema.     

Expression and localization of aquaporins in rat gastrointestinal tract

A family of water-selective channels, aquaporins (AQP), has beendemonstrated in various organs and tissues. However, the localizationand expression of the AQP family members in the gastrointestinal tracthave not been entirely elucidated. This study aimed to demonstrate theexpression and distribution of several types of the AQP family and tospeculate on their role in water transport in the rat gastrointestinal tract. By RNase protection assay, expression of AQP1-5 and AQP8 was examined in various portions through the gastrointestinal tract.AQP1 and AQP3 mRNAs were diffusely expressed from esophagus to colon,and their expression was relatively intense in the small intestine andcolon. In contrast, AQP4 mRNA was selectively expressed in the stomachand small intestine and AQP8 mRNA in the jejunum and colon.Immunohistochemistry and in situ hybridization demonstrated cellularlocalization of these AQP in these portions. AQP1 was localized onendothelial cells of lymphatic vessels in the submucosa and laminapropria throughout the gastrointestinal tract. AQP3 was detected on thecircumferential plasma membranes of stratified squamous epithelialcells in the esophagus and basolateral membranes of cardiac glandepithelia in the lower stomach and of surface columnar epithelia in thecolon. However, AQP3 was not apparently detected in the smallintestine. AQP4 was present on the basolateral membrane of the parietalcells in the lower stomach and selectively in the basolateral membranesof deep intestinal gland cells in the small intestine. AQP8 mRNAexpression was demonstrated in the absorptive columnar epithelial cellsof the jejunum and colon by in situ hybridization. These findings mayindicate that water crosses the epithelial layer through these waterchannels, suggesting a possible role of the transcellular route forwater intake or outlet in the gastrointestinal tract.     

Aquaporin molecular characterization in the sea-bass (Dicentrarchus labrax): the effect of salinity on AQP1 and AQP3 expression

Euryhaline fish possess the ability to compensate for environmental salinity changes through hydro-mineral regulation. A number of proteins have been studied in order to understand water and ion exchanges, known as fish osmoregulation. Sea-bass (Dicentrarchus labrax) cDNA sequences encoding a homologue of mammalian aquaporin (termed AQP1) and a homologue of mammalian aquaglyceroporin (termed AQP3) have been isolated and sequenced. The aquaporin amino acid sequences share respectively more than 60% and 65% identity with other known aquaporins. We have shown that salinity influences aquaporin expression levels in the gill, kidney and digestive tract, the main osmoregulatory organs. AQP1 may have a major osmoregulatory role in water transport in kidney and gut in SW-acclimated fish, whereas AQP3 could be implicated in gill water transport in FW-acclimated fish.     

两栖类消化道嗜银细胞和5-羟色胺细胞的研究进展

嗜银细胞属于内分泌细胞类,是消化道所含各类内分泌细胞的总称,5-羟色胺是其中含量和分布范围较广的一种胃肠激素。本文总结了两栖动物消化道嗜银细胞和5-羟色胺细胞的形态学特征、分布位置和分布密度规律,概述了冬眠、禁食和不同生活史阶段与两种细胞分布密度的关系。     

Expression,localization and possible functions of aquaporins 3 and 8 in rat digestive system

Although aquaporins (AQPs) play important roles in transcellular water movement, their precise quantification and localization remains controversial. We investigated expression levels and localizations of AQP3 and AQP8 and their possible functions in the rat digestive system using real-time polymerase chain reactions, western blot analysis and immunohistochemistry. We investigated the expression levels and localizations of AQP3 and AQP8 in esophagus, forestomach, glandular stomach, duodenum, jejunum, ileum, proximal and distal colon, and liver. AQP3 was expressed in the basolateral membranes of stratified epithelia (esophagus and forestomach) and simple columnar epithelia (glandular stomach, ileum, and proximal and distal colon). Expression was particularly abundant in the esophagus, and proximal and distal colon. AQP8 was found in the subapical compartment of columnar epithelial cells of the jejunum, ileum, proximal colon and liver; the most intense staining occurred in the jejunum. Our results suggest that AQP3 and AQP8 play significant roles in intestinal function and/or fluid homeostasis and may be an important subject for future investigation of disorders that involve disruption of intestinal fluid homeostasis, such as inflammatory bowel disease and irritable bowel syndrome.     

Aquaporin 9 expression along the male reproductive tract

Fluid movement across epithelia lining portions of the male reproductive tract is important for modulating the luminal environment in which sperm mature and reside, and for increasing sperm concentration. Some regions of the male reproductive tract express aquaporin (AQP) 1 and/or AQP2, but these transmembrane water channels are not detectable in the epididymis. Therefore, we used a specific antibody to map the cellular distribution of another AQP, AQP9 (which is permeable to water and to some solutes), in the male reproductive tract. AQP9 is enriched on the apical (but not basolateral) membrane of nonciliated cells in the efferent duct and principal cells of the epididymis (rat and human) and vas deferens, where it could play a role in fluid reabsorption. Western blotting revealed a strong 30-kDa band in brush-border membrane vesicles isolated from the epididymis. AQP9 is also expressed in epithelial cells of the prostate and coagulating gland where fluid transport across the epithelium is important for secretory activity. However, it was undetectable in the seminal vesicle, suggesting that an alternative fluid transport pathway may be present in this tissue. Intracellular vesicles in epithelial cells along the reproductive tract were generally poorly stained for AQP9. Furthermore, the apical membrane distribution of AQP9 was unaffected by microtubule disruption. These data suggest that AQP9 is a constitutively inserted apical membrane protein and that its cell-surface expression is not acutely regulated by vesicular trafficking. AQP9 was detectable in the epididymis and vas deferens of 1-wk postnatal rats, but its expression was comparable with adult rats only after 3--4 wk. AQP9 could provide a route via which apical fluid and solute transport occurs in several regions of the male reproductive tract. The heterogeneous and segment-specific expression of AQP9 and other aquaporins along the male reproductive tract shown in this and in our previous studies suggests that fluid reabsorption and secretion in these tissues could be locally modulated by physiological regulation of AQP expression and/or function.     

Functional morphology of the developing alimentary canal in the holothurian Eupentacta fraudatrix (Holothuroidea, Dendrochirota)

Development of the digestive tract of the holothurian Eupentacta fraudatrix was examined using light and transmission electron microscopy. After the blastopore closes, the gut rudiment loses its connection with the blastoderm and becomes an enclosed, tubular chamber, ending blindly at both ends. The differentiation of the digestive and coelomic epithelia is mainly completed by day 12. Since no transient cell types are observed, this differentiation is definitive. By day 20, the mouth and anal openings appear. The cuticular lining in the anterior part of the gut rudiment has an endodermal origin and differentiates before the mouth is formed. The rest of the gut lining is composed of enterocytes typical of holothuroid intestine. At the early stages of development, mitotic figures are encountered among nonspecialized cells of the gut primordium. In more developed digestive epithelium, vesicular enterocytes are capable of mitotic division. Dividing enterocytes retain secretory vacuoles; thus mitosis occurs in actually differentiated cells. After mouth and anus formation, the oesophagus, stomach, intestine and rectum can be distinguished. In the wall of the stomach, powerful musculature is formed.     

Enteric alpha-2 adrenoceptors: pathophysiological implications in functional and inflammatory bowel disorders

The gastrointestinal tract is innervated by extrinsic noradrenergic nerves which regulate various digestive functions, including mucosal secretions, bowel propulsion and gut sensations, via activation of alpha2-adrenoceptors. These receptors are mostly involved in the prejunctional modulation of enteric neurotransmission, but they act also at extra-neural postjunctional sites. Alpha2-adrenoceptor population consists of distinct subtypes, designated as alpha2A, alpha2B and alpha2C, endowed with different physiological and pharmacological properties, and the attempts to classify alpha2-adrenoceptors at gastrointestinal level have indicated a large predominance of alpha2A subtypes. Studies in humans have shown a favourable influence of alpha2-adrenoceptor activation on colonic tone and sensation, and there is clinical evidence indicating that alpha2-agonists can improve intestinal functions and induce a satisfactory relief of symptoms in patients with irritable bowel syndrome. In addition, genetic investigations have highlighted significant associations of alpha2-adrenoceptor gene polymorphisms with constipation and somatic symptoms in functional disorders of lower digestive tract. Post-operative ileus is a common surgical complication characterized by severe alteration of gut motility, resulting mainly from neurogenic and inflammatory mechanisms. Experiments in models of post-operative ileus have demonstrated an intense expression of alpha2-adrenoceptors in monocytes recruited into the intestinal muscularis, and provided consistent evidence that these receptors promote post-operative gut dysfunctions by hampering enteric neurotransmission and contributing to local inflammatory reaction. Changes in the enteric nervous system are being increasingly recognized also as major determinants of digestive symptoms associated with bowel inflammation. In this regard, studies based on functional and molecular approaches concur in suggesting that the expression of enteric alpha2-adrenoceptors is up-regulated in the presence of intestinal inflammation, and that alpha2-mediated mechanisms are responsible for gut motor alterations occurring at both inflamed and non-inflamed sites. The present review discusses pathophysiological implications of enteric alpha2-adrenoceptors, in the attempt to highlight potential therapeutic applications for drugs targeted on these receptors.     

云南盘鳇消化系统解剖学、组织学及消化酶活性研究

采用形态学、组织学及酶学方法对云南盘逗(Discogobio yunnanensis)成体消化系统进行研究。结果表明, 云南盘逗消化系统有以下特征: 口下位, 口腔上皮分布有较多味蕾及杯状细胞, 食道粗大, 含有大量黏液细胞, 无胃, 肠道较长, 盘旋于体腔中, 成鱼盘旋10回, 肠道系数为5.06±0.61, 肠分为前中后三段, 肠腔中密布肠绒毛。消化腺为肝胰脏, 肝脏分为左右两叶, 胰脏弥散分布在肝脏中。消化系统不同部位消化酶活性大小不同, 脂肪酶活性: 肝胰脏>前肠>中肠>后肠, 胰蛋白酶、淀粉酶、碱性磷酸酶活性: 前肠>中肠>肝胰脏>后肠。云南盘逗口下位, 食道粗短, 肠道细长, 肠绒毛丰富, 肠道含较高的胰蛋白酶和淀粉酶活性, 消化系统所具有的这些特征与其以固着藻类为食有关。     

Vasoactive intestinal polypeptidergic innervation and gastroenteropancreatic system: an immunocytochemical study in the hedgehog Erinaceus europaeus.

The pattern of the digestive vasoactive intestinal polypeptide (VIP)-ergic innervation is described immunohistochemically in the hedgehog Erinaceus europaeus. This animal is a small-sized, wild, nocturnal, lower eutherian mammal whose gastrointestinal tract shows some similarities with the avian gut. The myenteric plexus of the stomach, the mucosa of the small intestine and the circular muscle layer of the large intestine are the best VIP-innervated structures. The pattern of the positive innervation is similar to that described in other mammals and in some bird species. The widespread diffusion of the neuropeptide in the gut is probably due to the importance of its functions in the digestive physiology.     

南方大口鲇消化道细菌群落结构与其胃肠分化的关系

以肉食性南方大口鲇(Silurus soldatovi meridonalis Chen)为对象, 研究采用PCR-DGGE指纹技术对其仔稚鱼胃肠道分化过程及细菌群落结构进行了对比分析, 进而探讨了细菌群落与胃肠道分化的关系。消化道外部形态和胃肠切片显示13日龄样品起, 胃肠在结构上出现较大的分化。DGGE分析结果显示胃肠道细菌群落的分化始于18日龄:从18日龄样品起, 肠内细菌群落明显开始分化, 但在随后的1833日龄期间细菌群落结构相对稳定, 而胃内细菌群落则一直处于动态变化中。这说明, 南方大口鲇仔稚鱼的个体发育过程中, 随着胃肠在组织结构上的分化, 其消化道细菌群落结构也出现了明显分化, 并且胃和肠内细菌群落结构的分化在时间上存在差异。该研究结果将为深入研究胃和肠内细菌群落的功能差异提供基础资料。       

花臭蛙消化道6种激素阳性细胞的免疫组织化学定位

目的应用6种胃肠激素抗血清对花臭蛙（Rana schmackeri）消化道激素阳性细胞进行了免疫组织化学定位。方法SP（Streptavidin peroxidase）免疫组织化学法。结果五羟色胺阳性细胞在消化道各段都有分布,以胃幽门部密度最高,胃体其次,食道和直肠较少;生长抑素阳性细胞主要分布于胃和小肠,其中幽门部较多,食管和直肠未见分布。胃泌素阳性细胞只在十二指肠和空肠两个部位检测到。而胰多肽、胰高血糖素和P-物质阳性细胞在消化道各段均未见其分布。结论花臭蛙消化道这六种内分泌细胞分布与其他两栖类动物比较,既显示了两栖类动物在生活习性及动物消化生理方面消化道激素阳性细胞分布的某些共性,又显示了不同物种在消化道的结构特点、生活环境、食性等方面存在的种间差异。     

Transdifferentiation in holothurian gut regeneration

It has recently been shown that the whole spectrum of cell types constituting a multicellular organism can be generated from stem cells. Our study provides an example of an alternative mechanism of tissue repair. Injection of distilled water into the coelomic cavity of the holothurian Eupentacta fraudatrix results in the loss of the whole digestive tract, except the cloaca. The new gut reforms from two separate rudiments. One rudiment appears at the anterior end of the body and extends posteriorly. The second rudiment grows anteriorly from the cloaca. In the anterior rudiment, the luminal epithelium (normally derived from endoderm) develops de novo through direct transdifferentiation of the coelomic epithelial cells (mesodermal in origin). In the posterior rudiment, the luminal epithelium originates from the lining epithelium of the cloaca. After 27 days, the two rudiments come into contact and fuse to form a continuous digestive tube lined with a fully differentiated luminal epithelium. Thus in this species, the luminal epithelia of the anterior and posterior gut rudiments develop from two different cell sources-i.e., from the mesodermally derived mesothelium and the endodermally derived epithelium of the cloacal lining, respectively. Our data suggest that differentiated cells of echinoderms are capable of transdifferentiation into other cell types.