In situ hybridization of mRNA for the gastric H+,K(+)-ATPase in rat oxyntic mucosa

The Physiology of the Gastric Parietal Cell

Parietal cells are responsible for gastric acid secretion, which aids in the digestion of food, absorption of minerals, and control of harmful bacteria. However, a fine balance of activators and inhibitors of parietal cell-mediated acid secretion is required to ensure proper digestion of food, while preventing damage to the gastric and duodenal mucosa. As a result, parietal cell secretion is highly regulated through numerous mechanisms including the vagus nerve, gastrin, histamine, ghrelin, somatostatin, glucagon-like peptide 1, and other agonists and antagonists. The tight regulation of parietal cells ensures the proper secretion of HCl. The H+-K+-ATPase enzyme expressed in parietal cells regulates the exchange of cytoplasmic H+ for extracellular K+. The H+ secreted into the gastric lumen by the H+-K+-ATPase combines with luminal Cl- to form gastric acid, HCl. Inhibition of the H+-K+-ATPase is the most efficacious method of preventing harmful gastric acid secretion. Proton pump inhibitors and potassium competitive acid blockers are widely used therapeutically to inhibit acid secretion. Stimulated delivery of the H+-K+-ATPase to the parietal cell apical surface requires the fusion of intracellular tubulovesicles with the overlying secretory canaliculus, a process that represents the most prominent example of apical membrane recycling. In addition to their unique ability to secrete gastric acid, parietal cells also play an important role in gastric mucosal homeostasis through the secretion of multiple growth factor molecules. The gastric parietal cell therefore plays multiple roles in gastric secretion and protection as well as coordination of physiological repair.

Functional coupling of chloride-proton exchanger ClC-5 to gastric H+,K+-ATPase

It has been reported that chloride–proton exchanger ClC-5 and vacuolar-type H⁺-ATPase are essential for endosomal acidification in the renal proximal cells. Here, we found that ClC-5 is expressed in the gastric parietal cells which secrete actively hydrochloric acid at the luminal region of the gland, and that it is partially localized in the intracellular tubulovesicles in which gastric H⁺,K⁺-ATPase is abundantly expressed. ClC-5 was co-immunoprecipitated with H⁺,K⁺-ATPase in the lysate of tubulovesicles. The ATP-dependent uptake of ³⁶Cl⁻ into the vesicles was abolished by 2-methyl-8-(phenylmethoxy)imidazo[1,2-a]pyridine-3-acetonitrile (SCH28080), an inhibitor of H⁺,K⁺-ATPase, suggesting functional expression of ClC-5. In the tetracycline-regulated expression system of ClC-5 in the HEK293 cells stably expressing gastric H⁺,K⁺-ATPase, ClC-5 was co-immunoprecipitated with H⁺,K⁺-ATPase, but not with endogenous Na⁺,K⁺-ATPase. The SCH28080-sensitive ³⁶Cl⁻ transporting activity was observed in the ClC-5-expressing cells, but not in the ClC-5-non-expressing cells. The mutant (E211A-ClC-5), which has no H⁺ transport activity, did not show the SCH28080-sensitive ³⁶Cl⁻ transport. On the other hand, both ClC-5 and its mutant (E211A) significantly increased the activity of H⁺,K⁺-ATPase. Our results suggest that ClC-5 and H⁺,K⁺-ATPase are functionally associated and that they may contribute to gastric acid secretion.

Cellular distribution of NKCC2 in the gastric mucosa and its response to short-term osmotic shock

The Na(+)-K(+)-2Cl(-) cotransporter-2 (NKCC2) has long been recognized as a "kidney-specific" transporter and is important in salt reabsorption. NKCC2 has been found in the gastric mucosa; however, its cellular distribution and function remain obscure. The present study characterized the distribution pattern of NKCC2 in mammalian gastric mucosa and investigated its response to osmotic challenge. Reverse transcription with the polymerase chain reaction, Western blot and immunofluorescence were used to determine NKCC2 expression and localization. The effect of osmotic shock on NKCC2 expression was studied in isolated gastric mucosa with variable osmolarity treatment. Results from all of the above studies were compared with those of NKCC1. Our data indicated that NKCC1 and NKCC2 were expressed in the gastric mucosa of rat, mouse and human. The mRNA transcripts and proteins for NKCC1 and NKCC2 were broadly expressed in the rat gastric mucosa. In rat and mouse, NKCC1 was largely confined to the lower part of the oxyntic and pyloric gland areas, whereas NKCC2 extended throughout the gastric glands. NKCC1 immunoreactivity was strongly expressed in the parietal and chief cells but was weaker in the mucous cells. NKCC2 was abundantly located in the parietal and mucous cells but faintly distributed in the chief cells. Hypertonic treatment increased the protein level of NKCC1 and caused evident membrane translocation. In contrast, NKCC2 was significantly downregulated and no obvious membrane translocation was observed. Thus, NKCC2 displayed a more ubiquitous distribution in the gastric mucosa and might work coordinately with NKCC1 to maintain cell volume homeostasis under hypertonic conditions.

Altered expression of aquaporin 4 and H+/K+-ATPase in the stomachs of peptide YY (PYY) transgenic mice

BACKGROUND INFORMATION

The hormone PYY (peptide YY), synthesized by endocrine cells in the pancreas, ileum, colon and stomach has widespread inhibitory effects on gastrointestinal and pancreatic fluid secretion. Transgenic mice expressing a viral oncoprotein under the control of the PYY gene 5'-flanking region develop well-differentiated colonic endocrine tumours producing mainly PYY and enteroglucagon. In the present study, we investigated the expression of AQP4 (aquaporin 4) water channel and H(+)/K(+)-ATPase in stomachs from both control and transgenic mice.

RESULTS

Semi-quantitative RT (reverse transcriptase)-PCR showed an increase in the AQP4 transcript compared with control mice. Quantitative Western-blot analysis of stomachs from control and transgenic mice confirmed a significant increase in the 30 kDa AQP4 protein in transgenic mice. In control mice, AQP4 is specifically expressed in the basolateral membrane of gastric parietal cells, located in the basal region of the fundic glands. This particular location suggests that parietal cells in the base region of gastric pits might have a major role in water transport when compared with the more superficial parietal cells. Interestingly, immunofluorescence studies on transgenic mice revealed that the quantitative increase of AQP4 expression was actually due to an increase in the number of AQP4-expressing epithelial cells rather than to a higher expression of AQP4 in parietal cells. In fact, immunofluorescence experiments using the specific antibody raised against the AE2 isoform of Cl(-)/HCO3- exchanger specifically expressed in parietal cells confirmed that the number of parietal cells was comparable in both PYY and control stomachs. Moreover, in transgenic mice, a parallel significant decrease in the expression of H(+)/K(+)-ATPase was observed, as revealed by RT-PCR, quantitative immunoblotting and immunofluorescence.

CONCLUSIONS

In the present study, we demonstrate that the sustained inhibition of gastric secretion due to tumours producing PYY/enteroglucagon in transgenic mice is associated with an increase in AQP4 expression and a down-regulation of H(+)/K(+)-ATPase in parietal cells that acquire the characteristics of basal parietal cells. The absence of H2 receptors-mediated signalling due to the inhibition of histamine release from ECL (enterochromaffin-like) cells by PYY may be in part responsible for the observed increase in the number of parietal cells expressing AQP4.

Endoscopic analysis of gastric ulcer after one week's treatment with omeprazole and rabeprazole in relation to CYP2C19 genotype

In Japanese healthy CYP2C19 extensive metabolizers, rabeprazole 10 mg shows a faster onset of action and stronger inhibition of acid secretion than does omeprazole 20 mg on the first 3 days of administration. We evaluated gastric ulcer improvement after 1 week's treatment with rabeprazole or omeprazole in relation to CYP2C19 polymorphism. A 6-mm rubber disc was placed temporarily at the side of the ulcer for measurement of the ulcer area. The improvement ratios of ulcer area in homozygous extensive metabolizers (homoEMs), heterozygous extensive metabolizers (heteroEMs) and poor metabolizers (PMs) treated with rabeprazole 10 mg were 60.8, 65.0 and 55.3%, respectively, and these values are not significantly different. Corresponding values with omeprazole 20 mg were 46.3, 61.7 and 63.2%, respectively, and the value of homoEMs was significantly smaller than that of heteroEMs. The improvement ratios with rabeprazole in homoEMs and heteroEMs were significantly greater than that with omeprazole in homoEMs.

K+-Cl- Cotransporter-3a Up-regulates Na+,K+-ATPase in Lipid Rafts of Gastric Luminal Parietal Cells

Gastric parietal cells migrate from the luminal to the basal region of the gland, and they gradually lose acid secretory activity. So far, distribution and function of K+-Cl(-) cotransporters (KCCs) in gastric parietal cells have not been reported. We found that KCC3a but not KCC3b mRNA was highly expressed, and KCC3a protein was predominantly expressed in the basolateral membrane of rat gastric parietal cells located in the luminal region of the glands. KCC3a and the Na+,K+-ATPase alpha1-subunit (alpha1NaK) were coimmunoprecipitated, and both of them were highly localized in a lipid raft fraction. The ouabain-sensitive K+-dependent ATP-hydrolyzing activity (Na+,K+-ATPase activity) was significantly inhibited by a KCC inhibitor (R-(+)-[(2-n-butyl-6,7-dichloro-2-cyclopentyl-2,3-dihydro-1-oxo-1H-inden-5-yl)oxy]acetic acid (DIOA)). The stable exogenous expression of KCC3a in LLC-PK1 cells resulted in association of KCC3a with endogenous alpha1NaK, and it recruited alpha1NaK in lipid rafts, accompanying increases of Na+,K+-ATPase activity and ouabain-sensitive Na+ transport activity that were suppressed by DIOA, whereas the total expression level of alpha1NaK in the cells was not significantly altered. On the other hand, the expression of KCC4 induced no association with alpha1NaK. In conclusion, KCC3a forms a functional complex with alpha1NaK in the basolateral membrane of luminal parietal cells, and it up-regulates alpha1NaK in lipid rafts, whereas KCC3a is absent in basal parietal cells.

Parietal cell density during gastric ulcer healing in the rat

BACKGROUND

During the healing of gastric ulcers, extensive changes take place in the structure and proportion of the parietal cells in the ulcer margin. We aimed to determine whether these changes are influenced by compounds or by procedures that may promote or delay gastric ulcer healing.

METHODS

Acetic acid ulcers were produced in the rat gastric corpus; control rats were non-operated or sham-operated. All rats were provided with an osmotic minipump releasing 3H-thymidine for determination of the labelling index (LI). The rats were given omeprazole, gastrin or indomethacin, infected with Helicobacter pylori, or subjected to anterior vagotomy. They were killed after 1, 2, 6 or 13 days, and the ulcer margin and undamaged corpus wall were excised for histology. The proportion of parietal cells was calculated in relation to the total number, and the total volume, of the epithelial cells.

RESULTS

The parietal cells averaged 16%-21% of the number and 30%-32% of the volume of the epithelial cells in the unoperated control rats, but considerably less in the ulcer margin. This reduction was partially prevented by indomethacin. In the undamaged, dorsal epithelium the parietal cells increased to 23%-26% of the number, and 41%-47% of the volume, of the epithelial cells, both in the ulcer rats and in the sham-operated rats. The LI of the parietal cells was 6% in the undamaged epithelium of the 13-day ulcer rats, but close to 0% in all other groups examined.

CONCLUSION

Indomethacin prevents much of the loss of parietal cells in the ulcer margin. In the undamaged epithelium of the ulcer rats there is an increased proportion of parietal cells. The new parietal cells are not formed directly from dividing cells, but are probably recruited from existing precursor cells.

Rat parietal cells express CCK(2) receptor mRNA: gene expression analysis of single cells isolated by laser-assisted microdissection

Gastrin plays a crucial role in maintaining a normal cellular composition and function of the oxyntic mucosa. It has been debated for decades whether parietal cells possess cholecystokinin-2 (CCK(2)) receptors and interact directly with gastrin. We investigated whether parietal cells express CCK(2) receptor mRNA by using new molecular biology techniques. Rat oxyntic mucosal cells were dispersed and enriched by elutriation, and single parietal and ECL cells were isolated from cell smears by means of laser microbeam microdissection and laser pressure catapulting. The mRNA from each single cell was isolated and subjected to one-step multiplex or conventional reverse transcription-polymerase chain reaction and subsequent nested PCR. Specific primers for the CCK(2) receptor were used in combination with primers for H,K-ATPase and histidine decarboxylase, specific markers for parietal and ECL cells, respectively. CCK(2) receptor mRNA was detected in 25% of the rat parietal cells and 40% of the ECL cells examined.

The expression of gastric H+-K+-ATPase mRNA and protein in developing rat fundic gland

The proton pump H+-K+-ATPase is the final common pathway mediating the production and secretion of hydrochloric acid by gastric parietal cells. The present studies were undertaken to examine whether the expression of gastric H+-K+-ATPase mRNA and protein changes are associated with the development of H+-K+-ATPase activity in the rat fundic gland. H+-K+-ATPase activity was examined in rat fundic gland at different stages from gestational day 18.5 to postnatal 8 weeks. The expression of H+-K+-ATPase mRNA was detected by in situ hybridization using a digoxigenin-labelled RNA probe with a tyramide signal amplification system. The expression of H+-K+-ATPase protein was evaluated by immunoblotting and immunohistochemistry using antibodies against H+-K+-ATPase alpha- and beta-subunits. We found that H+-K+-ATPase enzyme activity was detectable from the onset of gland formation (day 19.5 of gestation) and increased with age in the developing rat fundic gland. Expression of mRNA and protein was also discernible at the same time, and a progressive increase in expressions was observed as rats developed. Our results suggested that in developing rat fundic gland, the expression of both mRNA and protein of H+-K+-ATPase increased with age in a manner that parallels the development of H+-K+-ATPase enzyme activity.

Cholecystokinin-B/gastrin receptors enhance wound healing in the rat gastric mucosa

Although physiological functions of the CCK-B/gastrin receptor are well explored, little is known about its role during healing. Here, we evaluated the role of this receptor in the rat oxyntic mucosa following the introduction of a cryoulcer. In this model, we located and quantified CCK-B/gastrin receptors by reverse transcriptase PCR and receptor autoradiography. Rats with cryoulcers were treated with placebo, omeprazole, the CCK-B/gastrin receptor antagonist YF-476, omeprazole plus YF-476, gastrin-17, and gastrin 17 plus YF-476. During wound healing, CCK-B/gastrin receptors were specifically expressed and localized to the regenerative mucosal ulcer margin. This high expression was limited in time, and the pattern of expression of CCK-B/gastrin receptors correlated closely with the proliferative activity of the regenerative mucosa. Functionally, omeprazole and gastrin-17 caused profound hypergastrinemia, increased cell proliferation in the mucosal ulcer margin and accelerated the late ulcer healing phase. These effects were completely reversed by cotherapy with YF-476. These in vivo and vitro data suggest that CCK-B/gastrin receptors in regenerative rat gastric oxyntic mucosa enhance trophic effects during wound healing.

Parietal cells express high levels of Na-K-2Cl cotransporter on migrating into the gastric gland neck

Na-K-2Cl cotransport and Cl/HCO3 exchange are prominent mechanisms for Cl- uptake in Cl--secreting epithelial cells. We used immunofluorescence microscopy to delineate the distributions of Na-K-2Cl cotransporter-1 (NKCC1) and anion exchanger-2 (AE2) proteins in rat gastric mucosa (zymogenic zone). Parietal cells (PCs) above the neck of the gastric gland contained abundant AE2 but little or no NKCC1, whereas those in the neck and base contained high NKCC1 but diminished AE2. Lower levels of NKCC1 were detected in surface mucous cells and in cells comprising the blind ends of all glands. Pulse labeling of proliferating cells with bromodeoxyuridine indicated that new PCs originate in the isthmus with scant NKCC1; the subset of PCs that migrate downward expresses NKCC1 abruptly on entering the neck, within 7 days of cell division. Our results suggest that downwardly migrating PCs replace one mechanism for Cl- entry (Cl/HCO3 exchange) with another (Na-K-2Cl cotransport).

A rat model of chronic Helicobacter pylori infection. Studies of epithelial cell turnover and gastric ulcer healing

BACKGROUND

Our aim was to infect rats with Helicobacter pylori and to study the effects of the infection on the gastric mucosa in normal and in ulcer-operated rats.

METHODS

A mouse-adapted H. pylori (cagA-, VacA-) strain was inoculated into 23 rats. Another 20 uninfected rats served as controls. Two months later a gastric ulcer was induced in some rats. The animals were killed 3, 6, or 15 days after the ulcer operation. Tissues were taken for histology and for culture of H. pylori. Serum antibodies were determined.

RESULTS

All inoculated rats were infected by H. pylori after 2 months, mainly in the antrum. In these rats a mild to moderate chronic inflammation and a significantly increased frequency of apoptotic cells were observed in the antrum and in the ulcer margin, the ulcer healing was delayed, and the serum level of H. pylori-specific Ig was increased.

CONCLUSIONS

H. pylori infection in rats was successful and was accompanied by a mild to moderate mucosal inflammation. Gastric ulcer healing was delayed in infected rats, probably due to the inflammation and the increased apoptosis in epithelium.

The expression of pepsinogen c mRNA in normal gastroduodenal mucosa and the gastric ulcer margin of the rat

During the healing of experimental gastric ulcers in the oxyntic mucosa, there is a dedifferentiation of the glands in the ulcer margin: previous studies have shown that the parietal cells lose their capacity to produce HCl, and mucous cells replace the zymogen cells. Primarily, we wished to investigate whether or not the glands of the ulcer margin transcribe mRNA for pepsinogen; secondly we also wanted to locate such transcription in other parts of the gastroduodenal epithelium. For this purpose, we first established the baseline for distribution of pepsinogen mRNA in normal rats. We then studied its location in the margin of ulcers in the corpus region after 1-15 days of healing. Formaldehyde-fixed paraffin sections were used for in situ hybridization of mRNA for pepsinogen C, utilizing radioactive riboprobes. The normal gastroduodenal mucosa showed widespread hybridization: the signal was particularly strong in the zymogen cells; weaker signals were obtained from the mucous neck cells, and the cells of the cardiac, antral, and Brunner glands. Specific hybridization was weak or absent in the ulcer margin during the entire period studied. It is concluded that the capacity to produce pepsinogen C is significantly reduced or absent in the gastric ulcer margin during the first 15 days of healing; this should reduce the risks of peptic attack on the delicate scar and margin tissues during ulcer healing.