Crypt Colonocytes Research Articles

Correction of Chloride Transport and Mislocalization of CFTR Protein by Vardenafil in the Gastrointestinal Tract of Cystic Fibrosis Mice

Although lung disease is the major cause of mortality in cystic fibrosis (CF), gastrointestinal (GI) manifestations are the first hallmarks in 15–20% of affected newborns presenting with meconium ileus, and remain major causes of morbidity throughout life. We have previously shown that cGMP-dependent phosphodiesterase type 5 (PDE5) inhibitors rescue defective CF Transmembrane conductance Regulator (CFTR)-dependent chloride transport across the mouse CF nasal mucosa. Using F508del-CF mice, we examined the transrectal potential difference 1 hour after intraperitoneal injection of the PDE5 inhibitor vardenafil or saline to assess the amiloride-sensitive sodium transport and the chloride gradient and forskolin-dependent chloride transport across the GI tract. In the same conditions, we performed immunohistostaining studies in distal colon to investigate CFTR expression and localization. F508del-CF mice displayed increased sodium transport and reduced chloride transport compared to their wild-type littermates. Vardenafil, applied at a human therapeutic dose (0.14 mg/kg) used to treat erectile dysfunction, increased chloride transport in F508del-CF mice. No effect on sodium transport was detected. In crypt colonocytes of wild-type mice, the immunofluorescence CFTR signal was mostly detected in the apical cell compartment. In F508del-CF mice, a 25% reduced signal was observed, located mostly in the subapical region. Vardenafil increased the peak of intensity of the fluorescence CFTR signal in F508del-CF mice and displaced it towards the apical cell compartment. Our findings point out the intestinal mucosa as a valuable tissue to study CFTR transport function and localization and to evaluate efficacy of therapeutic strategies in CF. From our data we conclude that vardenafil mediates potentiation of the CFTR chloride channel and corrects mislocalization of the mutant protein. The study provides compelling support for targeting the cGMP signaling pathway in CF pharmacotherapy.

Clinical significance of colonic intraepithelial lymphocytosis in a pediatric population

The significance of colonic intraepithelial lymphocytosis has been well described in adults, and is associated with lymphocytic colitis, untreated celiac disease, and medications, among others. Little is known about the meaning of colonic intraepithelial lymphocytosis in the pediatric population; this study examines this finding in a cohort of children. Twenty patients in whom colonic intraepithelial lymphocytosis was a prominent feature were identified from 1999 to 2005. Colonic intraepithelial lymphocytosis was defined as 20 or more intraepithelial lymphocytes per 100 colonocytes present in at least one colonic mucosal biopsy. Each biopsy was examined for numbers of intraepithelial lymphocytes per 100 surface and crypt colonocytes; various architectural, inflammatory, and metaplastic changes were also noted. When available, concurrent duodenal and/or ileal biopsies were examined. Studied clinical parameters included indications for biopsy, clinical follow-up, final diagnosis, comorbidities, autoimmune serologies, and medications. A total of 121 colonic mucosal biopsies were examined in 20 patients who ranged from 1 to 17 years (mean 10.2 years; 40% male). Common indications for endoscopy included diarrhea and abdominal pain. A mean of 29 (±22) intraepithelial lymphocytes per 100 enterocytes were seen. Seven patients had colonic intraepithelial lymphocytosis as the only histologic finding. The remaining 13 patients had additional architectural, inflammatory, and metaplastic changes. The mean follow-up period was 14 months (range 1–48 months). Inflammatory bowel disease was diagnosed in 4 of 20 patients and was seen chiefly in biopsies in which colonic intraepithelial lymphocytosis was associated with architectural or inflammatory changes. Common disease associations include celiac disease, lymphocytic colitis, and autoimmune enteropathy. Pediatric colonic intraepithelial lymphocytosis, in the absence of other histologic findings, is associated with various diseases, including celiac disease, lymphocytic colitis, and autoimmune enteropathy. Colonic intraepithelial lymphocytosis in the presence of other inflammatory changes indicates the possibility of idiopathic inflammatory bowel disease. These findings are similar to those seen in adults, with the exception of autoimmune enteropathy.

PGE 2 reduces net water and chloride absorption from the rat colon by targeting the Na +/H + exchanger and the Na +K +2Cl − cotransporter

An effect of PGE 2 on water and chloride absorption was already established in a previous work. This study is an attempt to find the mechanism of action of the prostaglandin by investigating the involvement of three major transporters namely the Na +–K +ATPase, the Na +/H + exchanger and the Na +K +2Cl − cotransporter. Rats were injected with PGE 2 and 15 min later, the colon was perfused in situ with Krebs Ringer buffer, and net water and chloride absorption were determined. When the involvement of the cotransporter and/or the exchanger was investigated, animals were injected with, respectively, furosemide and amiloride 10 min before PGE 2. Superficial and crypt colonocytes were then isolated and the protein expression of the Na +–K + ATPase and the Na +K +2Cl − was determined by western blot analysis. The effect of PGE 2 on the pump activity in presence or absence of the transporters’ inhibitors was also studied. PGE 2 decreased net water and chloride absorption from the colon, increased the Na +–K + ATPase activity in superficial cells and reduced it in crypt cells. The prostaglandin was found to stimulate secretion in superficial cells by targeting the Na +K +2Cl − symporter, and reduce absorption in crypt cells by targeting the Na +/H + antiporter. Changes in the activity of the pump are secondary to changes in the activity of the other transporters.

Aquaporin-8 Is Involved in Water Transport in Isolated Superficial Colonocytes from Rat Proximal Colon

Water is an essential nutrient because it must be introduced from exogenous sources to satisfy metabolic demand. Under physiologic conditions, the colon can absorb and secrete considerable amounts of water even against osmotic gradients, thus helping to maintain the body fluid balance. Here we describe studies on both aquaporin (AQP) expression and function using cells isolated from the superficial and lower crypt regions of the rat proximal colon. The expression of AQP-3, -4, and -8 in isolated colonocytes was determined by semiquantitative RT-PCR and by immunoblotting. The localization of AQP-8 in the colon was evaluated by immunohistochemistry. A stopped-flow light scattering method was used to examine osmotic water movement in isolated colonocytes. Moreover, the contribution of AQP-8 to overall water movement through isolated colonocytes was studied using RNA interference technology. Colonocytes from the proximal colon express AQP-3, -4, and -8 with increasing concentrations from the lower crypt cells toward those on the surface. Osmotic water permeability was higher in surface than in crypt colonocytes (P < 0.05); it was significantly inhibited by the water channel blocker dimethyl sulfoxide, and reversed by beta-mercaptoethanol (P < 0.05). Immunohistochemistry revealed a strong AQP-8 labeling in the apical membrane of the superficial colonocytes. Inhibition of aquaporin-8 expression by small interfering RNA significantly decreased osmotic water permeability (approximately 38%; P < 0.05). Current results indicate that aquaporin-8 may play a major role in water movement through the colon by acting on the apical side of the superficial cells.

Regulatory volume increase after secretory volume decrease in colonic epithelial cells under muscarinic stimulation.

To address the question of whether colonic secretory cells change their volume in response to carbachol (CCh) stimulation and, if so, the mechanisms involved therein, we used two-photon laser scanning microscopy to measure the volume of individual epithelial cells in the fundus region of crypts isolated from the guinea-pig distal colon. We also measured the volume of human colonic epithelial T84 cells using an electronic sizing technique. Both types of colonocytes responded to stimulation by CCh with shrinkage and then underwent a regulatory volume increase (RVI), even during continued stimulation by CCh. The secretory volume decrease (SVD) induced by CCh was antagonized by atropine, BAPTA loading and niflumic acid, a blocker of Ca(2+)-activated Cl(-) channels. An increase in the intracellular free [Ca(2+)] was observed with fura-2 during these volume responses to CCh. Removal of all Na(+) or K(+) or of most of the Cl(-) from the extracellular solution abolished the RVI, but not the preceding SVD. The RVI, but not the preceding SVD, was abolished by bumetanide, a blocker of the Na(+)-K(+)-2Cl(-) cotransporter. We conclude that guinea-pig crypt colonocytes and human T84 cells exhibit a cytosolic Ca(2+)-dependent SVD and undergo a subsequent RVI that is dependent on the operation of Na(+)-K(+)-2Cl(-) cotransporters.

The ΔF508 mutation results in loss of CFTR function and mature protein in native human colon

Background & Aims: Deletion of the codon for phenylalanine at position 508 (ΔF508) is the most frequent disease-causing mutation in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. In heterologous cells, defective processing of the ΔF508 protein results in endoplasmic reticulum retention, proteolytic degradation, and absence of adenosine 3′,5′-cyclic monophosphate (cAMP)-dependent plasma membrane Cl− conductance. However, data with respect to the processing block of ΔF508 protein in native epithelia are limited and conflicting. Methods: To characterize both the fate and function of ΔF508 protein in a native epithelium, we measured CFTR-mediated Cl− secretion, localization of the CFTR protein, and CFTR maturation in rectal biopsy specimens from normal individuals and ΔF508 homozygous patients with cystic fibrosis (CF). Results: Ussing chamber studies showed that cAMP-dependent and cholinergic Cl− secretion was absent from rectal tissues freshly excised from ΔF508 homozygous patients with CF. By immunohistochemistry, we detected wild-type but not ΔF508 CFTR at the luminal membrane of crypt colonocytes. By sequential immunoprecipitation and immunoblotting analyses, mature CFTR protein was detected in normal but not in ΔF508 homozygous tissues. Conclusions: Collectively, these data show that there is insufficient maturation and transport of ΔF508 CFTR from the endoplasmic reticulum to the apical membrane to support CFTR-mediated Cl− secretion in the CF colon.

Apical Na+/H+ exchange near the base of mouse colonic crypts.

Colonic crypts can absorb fluid, but the identity of the absorptive transporters remains speculative. Near the crypt base, the epithelial cells responsible for vectorial transport are relatively undifferentiated and often presumed to mediate only Cl- secretion. We have applied confocal microscopy in combination with an extracellular fluid marker [Lucifer yellow (LY)] or a pH-sensitive dye (2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein) to study mouse colonic crypt epithelial cells directly adjacent to the crypt base within an intact mucosal sheet. Measurements of intracellular pH report activation of colonocyte Na+/H+ exchange in response to luminal or serosal Na+. Studies with LY demonstrate the presence of a paracellular fluid flux, but luminal Na+ does not activate Na+/H+ exchange in the nonepithelial cells of the lamina propria, and studies with LY suggest that the fluid bathing colonocyte basolateral membranes is rapidly refreshed by serosal perfusates. The apical Na+/H+ exchange in crypt colonocytes is inhibited equivalently by luminal 20 microM ethylisopropylamiloride and 20 microM HOE-694 but is not inhibited by luminal 20 microM S-1611. Immunostaining reveals the presence of epitopes from NHE1 and NHE2, but not NHE3, in epithelial cells near the base of colonic crypts. Comparison of apical Na+/H+ exchange activity in the presence of Cl- with that in the absence of Cl- (substitution by gluconate or nitrate) revealed no evidence of the Cl--dependent Na+/H+ exchange that had been previously reported as the sole apical Na+/H+ exchange activity in the colonic crypt. Results suggest the presence of an apical Na+/H+ exchanger near the base of crypts with functional attributes similar to those of the cloned NHE2 isoform.

Nuclear thymidylate synthase expression, p53 expression and 5FU response in colorectal carcinoma.

Thymidylate synthase (TS) is a key enzyme in DNA synthesis and is inhibited by metabolites of the chemotherapeutic agent 5-fluorouracil (5FU). Nuclear expression of TS in human tissue in vivo has not been characterised and its clinicopathological correlates in malignancy are unknown. 52 cases of primary colorectal carcinoma (CRC) and 24 cases of matched metastatic carcinoma were studied immunohistochemically using the monoclonal antibody TS106. The degree of nuclear TS immunostaining correlated closely with levels of TS mRNA expression amongst 10 CRCs studied. Strong nuclear immunostaining was seen in normal basal crypt colonocytes and germinal centre cells, and in a varying proportion of adenocarcinoma cells. Amongst the primary carcinomas, higher TS nuclear expression was associated with prominent extracellular mucin production and right-sided location. Higher TS nuclear expression also showed a significant association with poorer response to protracted venous infusional 5FU therapy. There was no clear association between TS nuclear expression and Ki67 or p53 expression assessed immunohistochemically. There was a strong positive correlation between TS nuclear expression in primary and metastatic CRC but the latter generally showed higher expression than matched primary tumour tissue. These findings confirm the nuclear expression of TS protein in human cells in vivo and provide new insight into how such expression may relate to the behaviour of CRCs. © 2001 Cancer Research Campaign http://www.bjcancer.com

Apical Na+/H+ exchange near the base of mouse colonic crypts

Chu, Jingsong, Shaoyou Chu, and Marshall H. Montrose. Apical Na /H exchange near the base of mouse colonic crypts. Am J Physiol Cell Physiol 283: C358–C372, 2002; 10.1152/ajpcell.01380.2000.—Colonic crypts can absorb fluid, but the identity of the absorptive transporters remains speculative. Near the crypt base, the epithelial cells responsible for vectorial transport are relatively undifferentiated and often presumed to mediate only Cl secretion. We have applied confocal microscopy in combination with an extracellular fluid marker [Lucifer yellow (LY)] or a pH-sensitive dye (2 ,7 -bis(2carboxyethyl)-5(6)-carboxyfluorescein) to study mouse colonic crypt epithelial cells directly adjacent to the crypt base within an intact mucosal sheet. Measurements of intracellular pH report activation of colonocyte Na /H exchange in response to luminal or serosal Na . Studies with LY demonstrate the presence of a paracellular fluid flux, but luminal Na does not activate Na /H exchange in the nonepithelial cells of the lamina propria, and studies with LY suggest that the fluid bathing colonocyte basolateral membranes is rapidly refreshed by serosal perfusates. The apical Na /H exchange in crypt colonocytes is inhibited equivalently by luminal 20 M ethylisopropylamiloride and 20 M HOE-694 but is not inhibited by luminal 20 M S-1611. Immunostaining reveals the presence of epitopes from NHE1 and NHE2, but not NHE3, in epithelial cells near the base of colonic crypts. Comparison of apical Na /H exchange activity in the presence of Cl with that in the absence of Cl (substitution by gluconate or nitrate) revealed no evidence of the Cl -dependent Na /H exchange that had been previously reported as the sole apical Na /H exchange activity in the colonic crypt. Results suggest the presence of an apical Na /H exchanger near the base of crypts with functional attributes similar to those of the cloned NHE2 isoform.

Dietary regulation and localization of apoptosis cascade proteins in the colonic crypt.

This study was designed primarily to assess the localization of apoptosis cascade proteins along the rat colonic crypt and secondarily to test whether the activity and/or localization of these proteins are affected by the enrichment of the diet with the soluble fiber pectin. Expression of apoptosis cascade proteins was assessed in isolated colonocytes harvested from the luminal and basal crypt colonocyte populations. Two different dietary regimens were tested: a standard diet (diet A), and a diet enriched in pectin (diet B), a soluble fiber that undergoes fermentation in the cecum and produces high concentrations of intracolonic short-chain fatty acids. Caspase-1 expression was maximal in luminal colonocytes of rats fed diet B, as evidenced by Western blot and immunohistological analyses. Expression of the cleaved poly(ADP-ribose) polymerase product was elevated in both the luminal and basal colonocytes of the pectin-fed group, whereas in rats fed diet A, the expression was lower, especially in basal crypt colonocytes. The highest expression of the antiapoptotic protein Bcl-2 was observed in the lower compartments of the colonic crypt tissue and was maximal in the rat group fed a standard diet. The apoptotic index in colonocytes of rats fed diet B was higher than that measured in rats fed diet A. Cumulatively, our results indicate that apoptosis cascade proteins are differentially localized along the lumen-crypt axis, and their expression and activity may be controlled by dietary components. These results may, at least partially, account for the documented protective effect of butyrogenic fibers on colorectal cancer.

Effect of Shiga Toxin on NaCl Transport in Rat Distal Colon

Background: Shiga toxin causes net fluid secretion in rabbit jejunum by selectively targeting, and inhibiting protein synthesis in, absorptive villous cells. The effect of Shiga toxin on the colon, where it is presumably produced, is not known. This study was undertaken to investigate the effect of Shiga toxin on the rat distal colon. Methods: Net absorption of water and Na was determined by in vivo perfusion of closed loops of rat colon pre-exposed to Shiga toxin or saline. Unidirectional and net fluxes of 22Na and 36Cl were measured in vitro under voltage-clamp conditions across rat distal colon mucosa pre-exposed to Shiga toxin. Shiga toxin binding to sections of rat distal colon was localized by immunohistochemistry. Protein synthesis was measured in surface and crypt colonocytes with 3H-leucine incorporation. Results: In the in vivo perfusion studies net absorption of Na and water was increased in Shiga toxin-treated colon compared with controls (P < 0.01). In the studies carried out in vitro, JnetNa and JnetCl across Shiga toxin-treated mucosa were found to be significantly higher than in control tissue (P < 0.001 and P < 0.01, respectively). Net absorption of Na or Cl did not increase further in the presence of 25 mM butyrate, indicating the absence of short-chain fatty acids (SCFA)-linked NaCl absorption in Shiga toxin-treated colon. Moreover, Shiga toxin-treated colon failed to respond to theophylline, which induced secretion in the normal colon. Immunohistochemistry showed Shiga toxin binding to crypt cells but not to surface cells in the distal colon. Shiga toxin inhibited protein synthesis (by 27.3%) in crypt cells but not in surface cells (P < 0.05). Conclusions: An unexpected increase in water and NaCl absorption was noted in Shiga toxin-treated rat distal colon, which appears to result from selective effects of the toxin on secretory crypt cells.

5-HT Induces cAMP Production in Crypt Colonocytes at a 5-HT4Receptor

Previous studies demonstrate that both 5-hydroxytryptamine (5-HT) and cyclic AMP (cAMP) induce chloride efflux from crypt colonocytes in the rat distal colon; antagonist studies suggest that the 5-HT response is mediated primarily by the 5-HT4receptor. Since this receptor is known to be positively coupled to adenylate cyclase, we postulated that 5-HT should induce generation of cAMP, which should be inhibited by 5-HT4antagonists.Method.Mucosal cells from rat distal colon were taken by a sequential calcium chelation technique for enrichment of crypt cells. Cytokeratin stains demonstrated that >99% of cells were colonocytes. [3H]Thymidine uptake studies demonstrate a fivefold increased incorporation in this cell preparation compared to earlier fractions. 3-Isobutyl-l-methylxanthine (IBMX, 100 μM) was added to all cell suspensions in order to prevent cAMP metabolism. Cell suspensions were incubated for 2 min at 37°C with different concentrations of 5-HT (n= 7). cAMP was measured by enzyme immunoassay. In another series of experiments, 5-HT (0.3 μM) stimulation of cAMP was similarly measured in the presence and absence of 5-HT receptor antagonists: 10 μM 5-HTP-DP (5-HT1P;n= 4), 0.1 μM ketanserin (5-HT2A;n= 4), 0.3 μM ondansetron (5-HT3;n= 4), 3 μM tropisetron (5-HT3and 5-HT4;n= 4), and 10 nM GR-113808 (5-HT4;n= 5).Results.5-HT produced a dose-dependent increase in cAMP. The increase was significant at concentrations ≥0.3 μM when compared to cells incubated with IBMX alone. In the second series of experiment, 5-HT-induced generation of cAMP at a dose of 0.3 μM was significantly inhibited in the presence of GR-113808 and tropisetron.Conclusion.5-HT acts at a 5-HT4receptor to induce production of cAMP in rat distal crypt colonocytes.

Characterization of sodium and chloride conductances in preneoplastic and neoplastic murine colonocytes.

Glucocorticoids, such as dexamethasone, induce amiloride-sensitive Na+ conductances in rat distal colon epithelium. The activity of these conductances diminishes from the surface to the base of the crypt whereas cAMP-stimulated Cl- secretion decreases from the crypt base to the surface. These gradients are likely to be perturbed during carcinogenesis. We therefore determined the magnitude of Na+ and Cl- conductances in colonocytes isolated from normal and carcinogen-treated rats. Colon carcinogenesis was induced by injection of dimethylhydrazine (DMH) (18 mg/kg) for 5 weeks. Before sacrifice animals were treated for 3 days with dexamethasone. Colonocyte populations from the surface to the crypt base (C1-C5) were harvested from the distal colon by a Ca2+-chelating procedure. The activity of Na+ conductances was determined by uptake of 22Na+ by surface and crypt colonocyte populations and by membrane vesicles in the presence and absence of 10 microM amiloride. In control rats Na+ conductance was highest in surface colonocytes and absent in the crypt base. As early as 2 weeks after initiation of DMH treatment amiloride-inhibited Na+ uptake was virtually absent in the upper crypt. Transcriptional assessment of the alpha-, beta- and gamma-subunits that constitute the epithelial Na+ channel revealed that DMH treatment reduces the expression of beta-subunit mRNA. We then examined 36Cl- efflux from isolated colonocytes of normal and carcinogen-treated rats in response to forskolin (0.01 mM). Forskolin induced a marked rise in cAMP in lower crypt cells concomitant with a significant stimulation of 36Cl- efflux. Intracellular cAMP increased in upper crypt cells in response to forskolin without an increase in 36Cl- efflux. By contrast, upper crypt colonocytes from DMH-treated rats showed forskolin-stimulated efflux beginning 4 weeks after initiation of treatment. We conclude that induction of Na+ conductances by glucocorticoids is inhibited during the early stages of chemical carcinogenesis due to lack of induction of the beta-subunit of the channel. By contrast, Cl- transport is stimulated both in surface and lower crypt cell compartments during different stages of chemical carcinogenesis.

Altered Growth and Attachment of Rabbit Crypt Colonocytes Isolated from Different Developmental Stages

The rabbit colon was used to establish an in vitro model for examining development-related cellular changes in colonocyte function. Colonic epithelia from newborn, weanling, and adult animals were separated from the muscle and subjected to enzymatic digestion. A mixture of 0.05% Pronase, 0.015% collagenase IV, and 0.023% DTT was determined to be optimal for the isolation of newborn and weanling colonocytes. This solution yielded significantly more cells and of greater viability than a 0.1% Pronase, 0.03% collagenase IV, 0.07% DTT mixture that is optimal for adult colonocytes. The epithelial origin of the colonocytes was confirmed by immunofluorescent staining of cytokeratins. The isolation procedure resulted in a crypt-enriched population and the cell yield/g of mucosa increased with age as did the crypt depth. Colonocyte viability of adults but not of newborns and weanlings, declined from 24 to 72 h. When grown on plastic, the newborn and weanling colonocytes show a approximately 2-fold increase in number, DNA and protein content over 48 h. In contrast, for all three parameters the adult colonocytes revealed only a approximately 10% increase. The colonocytes also showed an age-related decline in attachment to extracellular matrices. Colonocytes showed maximal attachment to Matrigel and collagen IV; newborn and weanling colonocytes show > 80% attachment, whereas adult colonocytes showed only a 45% attachment. The efficacy of attachment to Matrigel compared with that on plastic also differed with age, representing 9.3-, 5.5-, and 4.4-fold increase in adult, weanling, and newborn colonocytes, respectively. Newborn and weanling colonocytes grown on Matrigel for 48 h, showed a significant, 15% increase in cell number, DNA, and protein content compared with those grown on plastic. There was no difference in these parameters when adult colonocytes grown on Matrigel were compared with those grown on plastic. In summary, we have established an in vitro model for studying colonic epithelial cells at different stages of development.

An apical permeability barrier to NH3/NH4+ in isolated, perfused colonic crypts.

Fermentation of nonabsorbed nutrients in the colon generates high concentrations of NH3/NH4+ in the colonic lumen. NH3 is a small, lipophilic neutral weak base that readily permeates almost all cell membranes, whereas its conjugate weak acid NH4+ generally crosses membranes much more slowly. It is not known how colonocytes maintain intracellular pH in the unusual acid-base environment of the colon, where permeant acid-base products of fermentation exist in high concentration. To address this issue, we hand dissected and perfused single, isolated crypts from rabbit proximal colon, adapting techniques from renal-tubule microperfusion. Crypt perfusion permits control of solutions at the apical (luminal) and basolateral (serosal) surfaces of crypt cells. We assessed apical- vs. basolateral-membrane transport of NH3/NH4+ by using fluorescent dyes and digital imaging to monitor intracellular pH of microvacuolated crypt cells as well as luminal pH. We found that, although the basolateral membranes have normal NH3/NH4+ permeability properties, there is no evidence for transport of either NH3 or NH4+ across the apical borders of these crypt cells. Disaggregating luminal mucus did not increase the transport of NH3/NH4+ across the apical border. We conclude that, compared to the basolateral membrane, the apical border of crypt colonocytes has a very low permeability-area product for NH3/NH4+. This barrier may represent an important adaptation for the survival of crypt cells in the environment of the colon.

Extracellular pH regulation in microdomains of colonic crypts: effects of short-chain fatty acids.

It has been suggested that transepithelial gradients of short-chain fatty acids (SCFAs; the major anions in the colonic lumen) generate pH gradients across the colonic epithelium. Quantitative confocal microscopy was used to study extracellular pH in mouse distal colon with intact epithelial architecture, by superfusing tissue with carboxy SNARF-1 (a pH-sensitive fluorescent dye). Results demonstrate extracellular pH regulation in two separate microdomains surrounding colonic crypts: the crypt lumen and the subepithelial tissue adjacent to crypt colonocytes. Apical superfusion with (i) a poorly metabolized SCFA (isobutyrate), (ii) an avidly metabolized SCFA (n-butyrate), or (iii) a physiologic mixture of acetate/propionate/n-butyrate produced similar results: alkalinization of the crypt lumen and acidification of subepithelial tissue. Effects were (i) dependent on the presence and orientation of a transepithelial SCFA gradient, (ii) not observed with gluconate substitution, and (iii) required activation of sustained vectorial acid/base transport by SCFAs. Results suggest that the crypt lumen functions as a pH microdomain due to slow mixing with bulk superfusates and that crypts contribute significant buffering capacity to the lumen. In conclusion, physiologic SCFA gradients cause polarized extracellular pH regulation because epithelial architecture and vectorial transport synergize to establish regulated microenvironments.

PROTRACTED DIARRHOEA AND AUTOIMMUNE ENTEROPATHY: A GENERALISED AUTOIMMUNE GUT DISORDER WITH A COMMON HLA HAPLOTYPE

In children with protracted diarrhoea, circulating enterocyte auto-antibodies (Ec Ab's) and an enteropathy, diarrhoea may persist despite therapy. we have examined the colon endoscopically in 17 such patients. Multiple biopsies were studied histologically, and by immunocytochemistry for HLA class II expression and T cell populations, and compared with histologically normal colon from control subjects. In addition, in view of the probable autoimmune nature of the diarrhoea HLA typing was done. 14/17 patients had a colitis characterised endoscopically by oedema and patchy erythema throughout the colon, and histologically by an inflammatory infiltrate of lymphocytes and plasma cells without crypt dysplasia, goblet cell changes or epitheloid granulomas. Class II (DR complex) expression was absent in both surface and crypt colonocytes of histologically normal colon (controls and 3/17 patients), but aberrant expression of DR molecules was seen in the 14 patients with a colitis. DR + ve lamina propria lymphomononuclear cells were present in patients and controls. Intraepithelial T cells were increased in 1 of 2 patients examined, and were CD8 + ve. On peripheral blood HLA typing patients were predominantly HLA CW7 (67%), DR3 (58%) and commonly B8 (38%). Our data shows that the HLA type in children with autoiimune enteropathy is consistent with that seen in other auto-inmune diseases, and in over 80% intestinal inflammation extends to the colon where colonccytes may perpetuate the disease by acting as antigen presenting cells.