Developmental changes in the inner surface structure of the bovine large intestine

The developmental pattern of the bovine fetal large intestine was studied with particular reference to the appearance and decline of the intestinal villi during the fetal period. In the bovine large intestine, the first rudimentary villus and goblet cells were seen in the rectum in a fetus estimated to be 3 months old. By 5-6 months, the goblet cells, absorptive cells in the intestinal crypts, and vacuolated cells in the villi were present along all segments of the large intestine. By 8-9 months, the villi have disappeared from the colon and rectum, epithelial cells no longer contain vacuoles, and absorptive and goblet cell populations are emerging from the crypts. These histological results suggest that development in the bovine large intestine follows a recto-cecal gradient and the most distinct turning point during the fetal period is the first disappearance of fetal villi in the rectum of fetuses estimated to be 7 months old. After this stage, the mucous membrane of the colon and rectum matured rapidly before birth. In contrast, the cecum may seem to require further development in perinatal life.     

Structure and permeability of goblet cell tight junctions in rat small intestine

Summary Two major cell types, goblet and absorptive cells, dominate the epithelial lining of small intestinal villi. We used freezefracture replicas of rat ileal mucosa to examine the possibility that tight junction structure, known to relate to transepithelial resistance, might vary with cell type. Tight junctions between absorptive cells were uniform in structure while those associated with villus goblet cells displayed structural variability. In 23% of villus goblet cell tight junctions the strand count was less than 4 and in 30% the depth was less than 200 nm. In contrast, only 4% of absorptive cell tight junctions had less than 4 strands and only 9% had depth measurements less than 200 nm. Other structural features commonly associated with villus goblet cell tight junctions but less commonly with absorptive cell tight junctions were: deficient strand cross-linking, free-ending abluminal strands, and highly fragmented strands. Bothin vivo ileal segments and everted loops were exposed to ionic lanthanum. Dense lanthanum precipitates in tight junctions and paracellular spaces were restricted to a subpopulation of villus goblet cells and were not found between villus absorptive cells. After exposure of prefixed ileal loops to lanthanum for 1 hour, faint precipitates of lanthanum were found in 14% of tight junctions and paracellular spaces between absorptive cells compared to 42% of tight junctions and paracellular spaces adjacent to villus goblet cells. When tested in Ussing chambers, the methods used for lanthanum exposure did not lower transepithelial resistance. Everted loops exposed to ionic barium and examined by light microscopy showed dense barium precipitates in the junctional zone and region of the paracellular space of villus goblet cells but not in these regions between absorptive cells. However, the macromolecular tracers, microperoxidase, cytochromec and horseradish peroxidase, were excluded from both villus goblet cell and absorptive cell paracellular spaces inin vivo segments. These findings suggest that a subpopulation of villus goblet cells may serve as focal sites of high ionic permeability and contribute to the relatively low resistance to ionic flow which characterizes the small intestinal epithelium.     

Morphological effects of a large single dose of cycloheximide on the intestinal epithelium of the rat.

Adult male rats received 15 mg/kg cycloheximide and the subsequent morphological effects at three and six hours after injection were evaluated using histometry, light and electron microscopy, histological demonstration of terminal web and acid phosphatase, and radioautography with tritiated thymidine. Rapid atrophy of the villi took place, progressing from the villus tip by premature exfoliation of epithelial cells. The crypts also diminished by random exfoliation of many crypt cells and by partial or complete disintegration. Mitosis and epithelial cell migration were absent. By six hours, the area occupied by the villi and the crypts per unit length of histological section was decreased by about 70-90% in most of the small intestine but only by about 40-60% in the duodenum and the terminal ileum. In the upper half of the villi, the epithelium was strongly positive for acid phosphatase and contained large numbers of round bodies resembling primary lysosomes. In the lower half, the microvillous border and terminal web were found to be disrupted. Animals receiving only 5 mg/kg cycloheximide also showed the atrophy of villi and crypts, and the round bodies resembling lysosomes. Evidence from several sources has indicated that protein synthesis in normal villus epithelial cells subsides toward the villus tip and becomes minimal at exfoliation. At exfoliation, proteins responsible for epithelial cohesion probably fail because they are no longer replenished. Cycloheximide appears to accelerate this process.     

Crypt cell development in newborn rat small intestine

Three monoclonal antibodies were prepared against luminal membranes from small intestinal cells of 3-d-old rats (YBB 1/27, YBB 3/10) and crypt cell membranes from adult rats (CC 4/80). The antibodies were shown to define specific stages of development of the intestinal crypt cells. The YBB 1/27 antigen was first detected at the luminal membrane of the epithelial cells in fetal intestine at day 20 of gestation; it was confined to the crypt cells and lower villus cells between 1 and 20-22 d after birth, and could not be detected in any region of the intestine in older animals. The YBB 3/10 antigen, identified as a set of high Mr proteins, was localized over the entire surface membrane of fetal intestinal cells and of crypt and villus cells after birth; after weaning (20-22 d after birth) it gradually disappeared from the villus cells and became confined to the region of the crypts. The CC 4/80 antigen, identified as a protein (or a set of related proteins) of molecular mass 28-34 kD, was shown to appear in the crypt cells 10-14 d after birth. Its distribution changed after weaning, when it disappeared from the crypts, and was localized in the absorptive lower villus cells. This change in pattern could, in part, be prematurely elicited by cortisone injection in younger animals. These results have demonstrated the presence of specific surface membrane components on the intestinal crypt cells, and suggested that fetal antigens may be retained in these cells after birth.     

Immunocytochemical localization of rat intestinal vitamin D-dependent calcium-binding protein

Vitamin D-dependent calcium-binding protein (CaBP) was localized in intestinal tissue sections obtained from rats raised under three different nutritional conditions: a normal vitamin D-replete diet, a vitamin D-free diet followed by supplementation with vitamin D3, or a vitamin D-free diet without additional supplementation. An indirect immunoperoxidase technique, with immunocontrols, was used to visualize the specific sites of CaBP. CaBP was visualized only in the cytoplasm of absorptive cells. In the duodenum of animals raised on a normal diet, CaBP was present in absorptive cells from the upper crypt region to the villus tips. In the jejunum, many fewer absorptive cells contained CaBP, while in the ileum only random absorptive cells near the villus tips contained CaBP. In rats raised on a vitamin D-deficient diet then supplemented with vitamin D3, CaBP was present in cells at the full depth of the crypts and in absorptive cells along the total villus length in the duodenum. Rats raised on the same deficient diet but without supplementation with additional vitamin D exhibited no CaBP in crypt cells nor in absorptive cells more than half way up the villi. Absorptive cells higher on the villi contained immunoreactive CaBP but the intensity of immunostaining and number of CaBP-containing cells was markedly reduced compared to the vitamin D-supplemented group.     

The influence of 400 r x-irradiation on the number and the localization of mature and immature goblet cells and Paneth cells in intestinal crypt and villus.

The influence of 400 R X-irradiation on the localization and the number of mature and immature goblet cells and Paneth cells in rat duodenal epithelium has been studied. At short times after irradiation, when the total proliferative activity in the crypts of Lieberkuhn is reduced, the proportion of mature and immature goblet cells of the total number of crypt cells was increased; also an absolute increase in the number of goblet cells in the crypts was found. The immature goblet cells were localized in the lower half of the crypt as in control animals, whereas the number of the mature cells increased over the whole crypt length. When the proliferative activity of the crypt cells increases again from 12 to 48 hr after irradiation the number of both types of goblet cells decreases. Between 48 and 72 hr, when the whole crypt is involved in proliferation, a second increase of both types of goblet cells was found. However, the localization of the immature goblet cells is no longer restricted to the lower half of the crypt but they also appear at the higher cell positions. On the villus no immature goblet cells were found and the changes in the numbers of mature goblet cells do reflect the changes induced by irradiation in the goblet cell population in the crypt. The absolute number and localization of Paneth cells did not change under the experimental conditions. The findings are discussed in relation to cell proliferation and differentiation processes in intestinal crypts.     

THE INFLUENCE OF 400 R X-IRRADIATION ON THE NUMBER and THE OCALIZATION OF MATURE and IMMATURE GOBLET CELLS and PANETH CELLS IN INTESTINAL CRYPT and VILLUS

The influence of 400 R X-irradiation on the localization and the number of mature and immature goblet cells and Paneth cells in rat duodenal epithelium has been studied. At short times after irradiation, when the total proliferative activity in the crypts of Lieberkiihn is reduced, the proportion of mature and immature goblet cells of the total number of crypt cells was increased; also an absolute increase in the number of goblet cells in the crypts was found. The immature goblet cells were localized in the lower half of the crypt as in control animals, whereas the number of the mature cells increased over the whole crypt length. When the proliferative activity of the crypt cells increases again from 12 to 48 hr after irradiation the number of both types of goblet cells decreases. Between 48 and 72 hr, when the whole crypt is involved in proliferation, a second increase of both types of goblet cells was found. However, the localization of the immature goblet cells is no longer restricted to the lower half of the crypt but they also appear at the higher cell positions. On the villus no immature goblet cells were found and the changes in the numbers of mature goblet cells do reflect the changes induced by irradiation in the goblet cell population in the crypt. The absolute number and localization of Paneth cells did not change under the experimental conditions. The findings are discussed in relation to cell proliferation and differentiation processes in intestinal crypts.     

Partitioning of paracellular conductance along the ileal crypt-villus axis: A hypothesis based on structural analysis with detailed consideration of tight junction structure-function relationships

Summary Current models of intestinal transport suggest cells which absorb ions are located on the villus while secretory cells are located in the crypt and putatively have paracellular pathways which are highly conductive to Na⁺. One approach to assess possible variation in small intestinal paracellular conductance along the crypt-villus axis is to morphometrically analyze the structural aspects of crypt and villus tight junctions (TJs) which relate to paracellular resistance. Such detailed analysis of junctional structure in this heterogeneous epithelium would permit one to compare intestinal TJ structure-function relationships with those in a structurally simpler epithelium such as that of toad urinary bladder. This comparison would also be of considerable interest since previous similar comparisons have failed to consider in detail the geometric dissimilarity between these two epithelia. We applied light, electron microscopic, and freezefracture morphometric techniques to guinea pig ileal mucosa to quantitatively assess, for both crypts and villi, linear TJ density, relative surface contributions, and TJ strand counts. Mean linear TJ densities were 76.8 m/cm² for crypt cells and 21.8 m/cm² for villus absorptive cells. Mean TJ strand counts were 4.45 for undifferentiated crypt cell TJs and 6.03 for villus absorptive cell TJs. The villus constituted 87% and the crypt 13% of total surface. We utilized these data to predict paracellular conductance of cryptsvs. villi based on equations derived from those of Claude (P. Claude,J. Membrane Biol. 39:219–232, 1978). Such analysis predicts that 73% of ileal paracellular conductance is attributable to the crypt. Furthermore, we obtained literature values for paracellular resistance in mammalian ileum and toad urinary bladder and for toad bladder TJ structure and linear density and constructed a relationship which would allow us to more accurately compare TJ structure-function correlates between these two epithelia. Such a comparison, which considers both surface amplification and TJ structure and distribution in these epithelia, shows that one would predictin vitro measured values for paracellular resistance should be approximately two orders of magnitude less in mammalian ileum than in toad urinary bladder. This predicted discrepancy (115-fold) correlates well with the observed difference (100-fold). These findings suggest that highly similar TJ structure-function relationships apply to these geometrically dissimilar tissues and that, in mammalian ileum, the crypt compartment may be responsible for the majority of net ileal paracellular conductance. We speculate that high crypt linear TJ density and low crypt TJ strand counts may serve as the structural basis of massive paracellular Na⁺ movement which is coupled to active Cl^– secretion and appears to originate from the crypt following exposure to intestinal secretagogues.     

EFFECT OF VILLUS LENGTH ON CELL PROLIFERATION AND MIGRATION IN SMALL INTESTINAL EPITHELIUM

For the interpretation of data supporting the hypothesis of a feedback regulation of proliferative activity in intestinal crypts by the functional villus cell compartment the life span and migration rate of epithelial cells on villi of experimentally reduced length should be known. Autoradiographic studies and scintillation counting of isolated villi at different time intervals after ³H-thymidine labelling were carried out 36, 48 and 60 hr intervals after X-irradiation. The results showed that the life span of epithelial cells in rat small intestine (36–48 hr) is independent of the villus length. In villi of reduced length the migration rate of the epithelial cells was found to be decreased compared with controls. Changes in the migration rate in turn seem to be dependent on the production of epithelial cells in the crypt. Comparative studies on the recovery of crypt and villus epithelium after various doses (300 and 700 R) of X-radiation support the hypothesis that increased proliferative activity in the crypt cell compartment is related to a reduction of the number of functional villus cells below a critical villus length. The importance of these findings in the interpretation of data on (micro) biochemical analyses of certain cell differentiation characteristics during increased proliferative activity is discussed.     

Histochemical characteristics of mucins in the small intestine. A comparative study of normal mucosa, benign epithelial tumours and carcinoma

Synopsis The histochemical properties of the mucins in seven benign epithelial tumours and 15 carcinomas distributed along the duodenum, jejunum and ileum were investigated and compared with normal controls. This study reveals that (a) goblet cells in normal small intestine contain neutral and sialomucins but no sulphated material; (b) the proportion of the different types of mucins in the goblet cells vary along the crypts and villi with an increasing amount of sialomucins towards the villus top; (c) mucin composition also changes from duodenum to ileum particularly in the proportions of sialic acid types and in the presence of traces of sulphomucins in the ileal mucosa close to the ileo-caecal valve, suggesting a gradual transition through the small intestine to the colon; (d) benign tumours show the same mucin pattern as normal mucosa; (e) the mucosa adjacent to carcinoma shows increasing amounts of sialomucins and sulphomucins; (f) carcinomas present a variety of mucin patterns, and thus the study of mucins seems to be of no value in differentiating tumours of the small intestine from those elsewhere in the gastrointestinal tract. A working hypothesis based on the Unitary Theory of the origin of the intestinal epithelial cells is proposed to explain the variations in glycoprotein synthesis with cell differentiation and carcinogenesis.     

Status of the mucous membrane of the jejunum of the rat after desympathization

Desympathization of the rat jejunum has been performed by means of periarterial sympathectomy of the cranial mesenteric artery. In total preparations of the jejunum wall, by means of water-aldehyde method, catecholamines have been revealed for controlling desympathization effectiveness. Signs of reinnervation appear in 180 days after the operation. In paraffin sections, stained by general histological methods, morphometric analysis of the most important parameters of the mucous membrane is performed (height of the villi, depth of the crypts, villus/crypt index, height of the epithelium, amount of goblet cells and interepithelial lymphocytes) Height of the villi and villus/crypt index increase in 1, 3 and 14 days, while in 7 days after the operation depth of the crypts increases, and the index mentioned decreases. Height of epithelium in the villi decreases in 14, 30 and 90 days. In 3-30 days after the operation amount of interepithelial lymphocytes increases.     

Mosaic analysis of small intestinal development using the<Emphasis Type="Italic"> spf</Emphasis><Superscript><Emphasis Type="Italic">ash</Emphasis></Superscript>-heterozygous female mouse

Mosaic analysis using the spf(ash)-heterozygous female mouse was performed to clarify the cell lineage and cell behavior during small intestinal development with special attention given to the villus and crypt formation. The spf(ash) mutation, located on the X-chromosome, causes ornithine transcarbamylase (OTC) deficiency, which leads to mosaic expression of this enzyme in the small intestine of the heterozygous female mouse. In the small intestine in heterozygous fetuses, very small patches, which were aggregates of OTC-positive cells or negative cells, with no definite orientation to the villus structures were observed. In the neonatal small intestine, the intervillus region (the presumptive crypts) was polyclonal, and the majority of crypts were comprised exclusively cells of either genotype in 2-week-old small intestine. These results suggest that extensive migration and cell mixing of small intestinal epithelial cells, which have no definite correlation with the villus formation, occur in fetal stages of development, and that the crypt morphogenesis commences after birth independently of the monoclonality of the epithelial cells. Our data with the mosaic mice also reconfirmed the monoclonality of the adult small intestinal crypts demonstrated in mouse aggregation chimeras.     

The influence of various cell kinetic conditions on functional differentiation in the small intestine of the rat. A study of enzymes bound to subcellular organelles

The process of cell maturation and cell ageing of absorptive epithelial cells was investigated in normal rat duodenum. The development of a number of enzymes bound to subcellular organelles was studied by using microchemical analyses on various cell compartments dissected from crypts and villi from freeze-dried cryostat sections. The development of the ultrastructural features of the absorptive epithelium was investigated by electron microscopy of various cell positions along the whole length of the crypt and the base of the villus. The data obtained were related to cell position along the crypt and villus and to cell age during migration from the bottom of the crypt to the tip of the villus.The influence of changes in the life-span of the cells and of increasing proliferative activity was studied by comparing normal rat duodenum with that from germfree rats and rats recovering from low radiation doses (72 hr after 400 R).Our data show that the specific activity of nonspecific esterases mainly localized in the endoplasmic reticulum increases when the cells migrate along the upper half of the crypt and the basal part of the villus. Activity of alkaline phosphatase, measured as a marker for the microvilli, is absent in the crypt, but increases linearly from the base of the villus to the tip. The longer life-span of villus cells in germfree animals does not result in a higher activity of these enzymes than in normal animals. An increased proliferative activity in the crypt, as present 72 hr after X-irradiation, is accompanied by a decreased activity of both enzymes but the pattern of activity during cell migration remains the same. The specific activity of enzymes bound to mitochondria or lysosomes (monoamineoxidase and β-N-acetylglucosaminidase) are not affected by changing crypt cell kinetics.Electrophoretic analyses of isolated cell compartments showed that the increase during normal differentiation or the decrease after X-irradiation of esterase activity is due to changes in overall activity, not to the appearance or disappearance of specific isoenzymes. Electron microscopy showed that in the normal intestine there is a gradual development of ultrastructural features during migration of the cell along the crypt while the most drastic changes in cell structure occur at the moment the cell enters the villus. Contrary to our expectation, the ultrastructural development was not influenced by increased proliferative activity in the crypt 72 hr after irradiation, and hence the decrease in enzyme activity found cannot be related to changes in ultrastructure.     

Diet, mucosal architecture and epithelial cell production in the small intestine of specified-pathogen-free and conventional rats.

Upper jejunum and terminal ileum were examined in specified-pathogen-free (SPF), conventional and conventional after SPF rearing (ex-SPF) rats. The effect of 2 differential diets on the last 2 groups was examined. Ex-SPF rats had taller villi and deeper crypts than SPF rats, but similar crypt to villus ratios and cell production rates. Ex-SPF rats had similar crypt depth and jejunal villus height to conventional rats on the same diet, but taller ileal villi and a lower cell production rate. Even after 6-8 weeks, in a conventional environment, ex-SPF rat intestine was still not identical with conventional rat intestine. Diet had a significant effect on mucosal architecture, and a smaller effect on cell production rate. It is concluded that diet, microbiological status of colony of origin, and environment after weaning, can all affect mucosal architecture and epithelial cell production, and should be properly controlled in experimental studies.     

Stand by me: Fibroblasts regulation of the intestinal epithelium during development and homeostasis

The epithelium of the small intestine is composed of a single layer of cells that line two functionally distinct compartments, the villi that project into the lumen of the gut and the crypts that descend into the underlying connective tissue. Stem cells are located in crypts, where they divide and give rise to transit-amplifying cells that differentiate into secretory and absorptive epithelial cells. Most differentiated cells travel upwards from the crypt towards the villus tip, where they shed into the lumen. While some of these cell behaviors are an intrinsic property of the epithelium, it is becoming evident that tight coordination between the epithelium and the underlying fibroblasts plays a critical role in tissue morphogenesis, stem-cell niche maintenance and regionalized gene expression along the crypt-villus axis. Here, we will review the current literature describing the interaction between epithelium and fibroblasts during crypt-villus axis development and intestinal epithelium renewal during homeostasis.     

Comparative immunohistolocalization of carbonic anhydrase isozymes I, II and III in the equine and bovine digestive tract

Summary Immunohistochemical localizations of carbonic anhydrase isozymes (CA-I, CA-II and CA-III) in equine and bovine digestive tracts were studied. In the horse, epithelial cells in both the oesophagus and non-glandular part of the stomach lacked all three isozymes. In contrast, surface epithelial and parietal cells in the glandular region of the stomach showed reactivity for CA-II. In the small intestine, absorptive columnar cells covering the villi in the duodenum were positive for CA-II. The epithelium of the jejunum and ileum lacked all three isozymes. In the large intestine, CA-II was detected in the columnar cells in the upper part of the crypt. In cattle, epithelial cells of the oesophagus showed reactions for CA-I and CA-III but not for CA-II. Although the absorptive epithelial cells of the small intestine lacked CA-I, CA-II and CA-III, those of the upper part of large intestine crypts were heavily stained for all three isozymes.     

Rapid expansion of intestinal secretory lineages following a massive small bowel resection in mice

Following massive small bowel resection (SBR) in mice, there are sustained increases in crypt depth and villus height, resulting in enhanced mucosal surface area. The early mechanisms responsible for resetting and sustaining this increase are presently not understood. We hypothesized that expansion of secretory lineages is an early and sustained component of the adaptive response. This was assessed in the ileum by quantitative morphometry at 12 h, 36 h, 7 days, and 28 days and by quantitative RT-PCR of marker mRNAs for proliferation and differentiated goblet, Paneth cell, and enterocyte genes at 12 h after 50% SBR or sham operation. As predicted, SBR elicited increases of both crypt and villus epithelial cells, which were sustained though the 28 days of the experiment. Significant increases in the overall number and percentage of both Paneth and goblet cells within intestinal epithelium occurred by 12 h and were sustained up to 28 days after SBR. The increases of goblet cells after SBR were initially observed within villi at 12 h, with marked increases occurring in crypts at 36 h and 7 days. Consistent with this finding, qRT-PCR demonstrated significant increases in the expression of mRNAs associated with proliferation (c-myc) and differentiated goblet cells (Tff3, Muc2) and Paneth cells (lysozyme), whereas mRNA associated with differentiated enterocytes (sucrase-isomaltase) remained unchanged. From these data, we speculate that early expansion of intestinal secretory lineages within the epithelium of the ileum occurs following SBR, possibly serving to amplify the signal responsible for initiating and sustaining intestinal adaptation.     

Histochemical studies of epithelial cell glycoproteins in normal rat colon

Two general classes of glycoproteins have been identified in the colonic epithelial cells of the Sprague Dawley rat. Glycoproteins belonging to the first of these classes contain sialic acids both with and without side chain o-acyl substituents, abundant o-sulphate ester and 'neutral sugars' (hexose, 6-deoxyhexose or N-acetyl hexosamine residues) with oxidisable vicinal diols and are located in the goblet cells of the descending colon and in goblet cells populating the upper halves of the crypts of the ascending colon. In the descending colon, the sulphosialoglycoproteins in the goblet cells in the base of the crypts contain sialic acids without side chain o-acyl substituents. It appears that as these cells migrate up the crypts, there is o-acylation of the side chains of the sialic acids of the glycoproteins and an increase in the quantity of 'neutral sugars' without a corresponding increase in sialic acid. Glycoproteins with similar properties to those of the goblet cells of the upper halves of the crypts of the descending colon, but containing less sulphate, are found in the goblet cells of the upper half of the crypts of the ascending colon. The second general class of glycoproteins contain sialic acids all, or almost all of which, are substituted at position C8 and only relatively small quantities of sulphate. They are located in the mucous cells of the descending colon, the deep crypt secretory cells of the ascending colon and the columnar absorptive cell brush border.(ABSTRACT TRUNCATED AT 250 WORDS)     

Physiological relevance of cell-specific distribution patterns of CFTR, NKCC1, NBCe1, and NHE3 along the crypt-villus axis in the intestine

We examined the cell-specific subcellular expression patterns for sodium- and potassium-coupled chloride (NaK2Cl) cotransporter 1 (NKCC1), Na(+) bicarbonate cotransporter (NBCe1), cystic fibrosis transmembrane conductance regulator (CFTR), and Na(+)/H(+) exchanger 3 (NHE3) to understand the functional plasticity and synchronization of ion transport functions along the crypt-villus axis and its relevance to intestinal disease. In the unstimulated intestine, all small intestinal villus enterocytes coexpressed apical CFTR and NHE3, basolateral NBCe1, and mostly intracellular NKCC1. All (crypt and villus) goblet cells strongly expressed basolateral NKCC1 (at approximately three-fold higher levels than villus enterocytes), but no CFTR, NBCe1, or NHE3. Lower crypt cells coexpressed apical CFTR and basolateral NKCC1, but no NHE3 or NBCe1 (except NBCe1-expressing proximal colonic crypts). CFTR, NBCe1, and NKCC1 colocalized with markers of early and recycling endosomes, implicating endocytic recycling in cell-specific anion transport. Brunner's glands of the proximal duodenum coexpressed high levels of apical/subapical CFTR and basolateral NKCC1, but very low levels of NBCe1, consistent with secretion of Cl(-)-enriched fluid into the crypt. The cholinergic agonist carbachol rapidly (within 10 min) reduced cell volume along the entire crypt/villus axis and promoted NHE3 internalization into early endosomes. In contrast, carbachol induced membrane recruitment of NKCC1 and CFTR in all crypt and villus enterocytes, NKCC1 in all goblet cells, and NBCe1 in all villus enterocytes. These observations support regulated vesicle traffic in Cl(-) secretion by goblet cells and Cl(-) and HCO(3)(-) secretion by villus enterocytes during the transient phase of cholinergic stimulation. Overall, the carbachol-induced membrane trafficking profile of the four ion transporters supports functional plasticity of the small intestinal villus epithelium that enables it to conduct both absorptive and secretory functions.