Estrogen synthesis in the stomach of Sprague-Dawley rats: comparison to Wistar rats

Aromatase, an estrogen synthase, exists in the gastric parietal cells of Wistar rats. The stomach synthesizes large amounts of estrogens and secretes them into the portal vein. We have been particularly studying gastric estrogen synthesis using Wistar rats. However, estrogen synthesis in the stomach of Sprague-Dawley (SD) rats, which are used as frequently as those of the Wistar strain, has not been clarified. We examined steroid synthesis in the stomach of SD rats using immunohistochemistry, in situ hybridization, Western blotting, real-time PCR, and LC-MS/MS. Aromatase also exists in the stomach of SD rats. Its distribution was not found to be different from that of Wistar rats. Results show that H+/K+-ATPase β-subunit and aromatase colocalized in double immunofluorescence staining. Each steroid synthase downstream from progesterone was present in the gastric mucosa. These results suggest that steroid hormones are synthesized in the parietal cells in the same pathway as Wistar rats. Although mRNA expression of steroid synthases were higher in SD, no significant difference was found in the amount of protein and each steroid hormone level in the portal vein. Although differences between strains might exist in steroid hormone synthesis, results show that SD rats are as useful as Wistar rats for gastric estrogen synthesis experimentation.

SYNTHESIS AND BIOLOGICAL EFFICACY OF NOVEL PIPERAZINE ANALOGUES BEARING QUINOLINE AND PYRIDINE MOIETIES

A series of novel piperazine analogues bearing quinolin-8-yloxy-butan--ones/pyridin-2-yloxy-ethanones were synthesized by a simple and convenient approach based on various substituted piperazine incorporating quinoline and pyridine moieties. The analogues were evaluated for in vitro antioxidant activity against 2,2-diphenyl-1-picryl-hydrazyl (DPPH) and ferrous ion radical scavenging activities and anti-inflammatory activity by inhibition of Vipera russelli venom (PLA2) and gastric K+/H(+)-ATPase activities. Most of the title compounds exhibited promising activity. Best antioxidant and PLA2-inhibiting activities were found for piperazine analogues with phenyl and nitro phenyl groups, whereas methoxy group on phenyl piperazine indicated selectivity for the H+/K(+)-ATPase.

[The state of lipid peroxidation and antioxidant protection system in parietal cells under experimental chronic atrophic gastritis development]

The lipid peroxidation state and the system functioning of antioxidant protection in parietal cells under rat chronic atrophic gastritis development was investigated. It was detected that the compensatory increase of superoxide dismutase and catalase activity did not affect the lipoperoxidation process and this resulted in accumulation of toxic TBA reactive substances and diene conjugates during the whole stages of the experimental pathology development. It was shown that the reserved power of the glutathione antioxidant system is sufficient to provide adoptable response in the acute period of the disease owing to increasing intracellular found of the reduced glutathione, but it is insufficient to prevent its decreasing in parietal cells in case of the chronic atrophic gastritis development. Our findings suggest that glutathione system is involved in processes of gastric atrophy. The obtained results testify about considerable system dysfunctions of lipid peroxidation and the antioxidant protection in processes of the rat experimental atrophic gastritis development.

Differential distribution of ghrelin-O-acyltransferase (GOAT) immunoreactive cells in the mouse and rat gastric oxyntic mucosa

The enzyme that acylates ghrelin was recently identified in mice as the fourth member of the membrane-bound O-acyltransferases superfamily (MBOAT4) and named ghrelin-O-acyltransferase (GOAT). Only one report showed GOAT mRNA expression in ghrelin-expressing cells of the mouse stomach. We investigated the distribution of GOAT protein in peripheral tissues and co-expression with endocrine markers in the gastric mucosa using a custom-made anti-GOAT antibody. Tissues were collected from male Sprague-Dawley rats and C57BL/6 mice. Western blot revealed two immunoreactive bands in rat and mouse gastric corpus mucosal proteins, a 50 kDa band corresponding to the GOAT protein and a 100 kDa band likely corresponding to a dimer. Western blot also detected GOAT in the plasma and levels were strongly increased after 24-h fasting in mice and slightly in rats. GOAT-immunoreactive cells were located in the gastric corpus mucosa and the anterior pituitary gland, whereas other peripheral tissues of rats and mice examined were negative. In mice, GOAT-immunoreactive cells were mainly distributed throughout the middle portion of the oxyntic glands, whereas in rats they were localized mainly in the lower portion of the glands. Double labeling showed that 95+/-1% of GOAT-immunoreactive cells in mice co-labeled with ghrelin, whereas in rats only 56+/-4% of GOAT-positive cells showed co-expression of ghrelin. The remainder of the GOAT-immunopositive cells in rats co-expressed histidine decarboxylase (44+/-3%). No co-localization was observed with somatostatin in rats or mice. These data suggest species differences between rats and mice in gastric GOAT expression perhaps resulting in a different role of the MBOAT4 enzyme in the rat stomach. Detection of GOAT in the plasma raises the possibility that ghrelin octanoylation may occur in the circulation and the fasting-induced increase in GOAT may contribute to the increase of acylated ghrelin after fasting.

Autoimmune Gastritis: Tolerance and Autoimmunity to the Gastric H+/K+Atpase (Proton Pump)

The alpha and beta subunits of the gastric H+/K(+)-ATPase (proton pump) have been identified as the major molecular targets of parietal cell autoantibodies associated with pernicious anaemia and with murine experimental autoimmune gastritis (EAG) induced by neonatal thymectomy. Recent studies with EAG suggest that the mechanisms of peripheral tolerance and autoimmunity to extrathymic autoantigens are mediated by subsets of "regulator" and "effector" CD4+ T cells, respectively. The persistence of "effector" CD4+ autoreactive T cells in the periphery may be a direct consequence of the delayed developmental expression of the target autoantigen. We hypothesize that cytokines produced by the "regulator" T cells prevent the clonal expansion of the "effector" autoreactive T cells, and that neonatal thymectomy induces organ-specific autoimmunity in genetically susceptible individuals by the reduction of the "regulator" T cell population.

Molecular dissection of HCl secretion in gastric parietal cells using streptolysin O permeabilization

Histamine-stimulated gastric acid secretion involves a transient elevation of intracellular Ca(2+) and the cyclic adenosine monophosphate (cAMP)-dependent protein kinase A (PKA) cascade through phosphorylation, the actions of which ultimately result in the fusion of vesicles containing H,K-ATPase (adenosine triphosphatase) to the apical plasma membrane of parietal cells. To dissect the signaling events underlying gastric acid secretion, we have developed a permeabilized gastric gland model using streptolysin O (SLO). The advantage of this model is its ability to retain cytosolic components that are required for the secretory machinery while granting accessibility for the introduction of macromolecules into the cytoplasm. Our studies showed that acid secretion in SLO-permeabilized glands is a cAMP-dependent process and involves the recruitment of H,K-ATPase-rich tubulovesicles into the apical plasma membrane as judged by biochemical assays. These studies established a functional permeabilized gland model in which the resting-to-secreting transition can be triggered by second messengers, while the manipulation of the cytoplasmic environment can be achieved with ease.

Incomplete synthesis of the Sda/Cad blood group carbohydrate in gastrointestinal cancer

Cancer-associated changes in cell surface carbohydrates, including incomplete synthesis of normal carbohydrate epitopes, strongly affect malignant and metastatic potential. Here, we report that compensating for the cancer-associated loss of a single glycosyltransferase, beta1,4N-acetylgalactosaminyltransferase T2, dramatically decreased cell surface expression of both E-selectin ligands (sialyl Lewis(x) and sialyl Lewis(a)). This modification was associated with elevated expression of the Sd(a) carbohydrate determinant, which is expressed in normal gastrointestinal mucosa and is strikingly downregulated in cancer tissues. Loss of E-selectin ligands resulted in decreased adhesion of cancer cells to activated human endothelial cells in vitro and eventually suppressed metastatic potential in vivo.

Modulatory role of phosphoinositide 3-kinase in gastric acid secretion

The gastric parietal cell is responsible for the secretion of HCl into the lumen of the stomach mainly due to stimulation by histamine via the cAMP pathway. However, the participation of several other receptors and pathways have been discovered to influence both stimulation and inhibition of acid secretion (e.g., cholinergic). Here we examine the role of phosphoinositide 3-kinase (PI3K) in the modulation of acid secretion. Treatment of isolated gastric glands and parietal cells with the PI3K inhibitor, LY294002 (LY), potentiated acid secretion in response to histamine to nearly the maximal secretion obtained with histamine plus phosphodiesterase inhibitors. As cAMP levels were elevated in response to histamine plus LY, but other means of elevating cAMP (e.g., forskolin, dbcAMP) were not influenced by LY, we posited that the effect might require activation of G-protein-coupled histamine H(2) receptors, possibly through the protein kinase B pathway (also known as Akt). Study of downstream effectors of PI3K showed that histaminergic stimulation increased Akt phosphorylation, which in turn was blocked by inhibition of PI3K. Expression studies showed that high expression of active Akt decreased acid secretion, whereas dominant-negative Akt increased acid secretion. Taken together, these data suggest stimulation with histamine increases the activity of PI3K leading to increased activity of Akt and decreased levels of cAMP in the parietal cell.

Functional role of bone morphogenetic protein-4 in isolated canine parietal cells

Bone morphogenetic protein (BMP)-4 is an important regulator of cellular growth and differentiation. Expression of BMP-4 has been documented in the gastric mucosa. We reported that incubation of canine parietal cells with EGF for 72 h induced both parietal cell morphological transformation and inhibition of H(+)/K(+)-ATPase gene expression through MAPK-dependent mechanisms. We explored the role of BMP-4 in parietal cell maturation and differentiation. Moreover, we investigated if BMP-4 modulates the actions of EGF in parietal cells. H(+)/K(+)-ATPase gene expression was examined by Northern blots and quantitative RT-PCR. Acid production was assessed by measuring the uptake of [(14)C]aminopyrine. Parietal cell apoptosis was quantitated by Western blots with anti-cleaved caspase 3 antibodies and by counting the numbers of fragmented, propidium iodide-stained nuclei. MAPK activation and Smad1 phosphorylation were measured by Western blots with anti-phospho-MAPK and anti-phospho-Smad1 antibodies. Parietal cell morphology was examined by immunohistochemical staining of cells with anti-H(+)/K(+)-ATPase alpha-subunit antibodies. BMP-4 stimulated Smad1 phosphorylation and induced H(+)/K(+)-ATPase gene expression. BMP-4 attenuated EGF-mediated inhibition of H(+)/K(+)-ATPase gene expression and blocked EGF induction of both parietal cell morphological transformation and MAPK activation. Incubation of cells with BMP-4 enhanced histamine-stimulated [(14)C]aminopyrine uptake. BMP-4 had no effect on parietal cell apoptosis, whereas TGF-beta stimulated caspase-3 activation and nuclear fragmentation. In conclusion, BMP-4 promotes the induction and maintenance of a differentiated parietal cell phenotype. These findings may provide new clues for a better understanding of the mechanisms that regulate gastric epithelial cell growth and differentiation.

A mechanism of Munc18b-syntaxin 3-SNAP25 complex assembly in regulated epithelial secretion

Syntaxin and Munc18 are essential for regulated exocytosis in all eukaryotes. It was shown that Munc18 inhibition of neuronal syntaxin 1 can be overcome by CDK5 phosphorylation, indicating that structural change disrupts the syntaxin-Munc18 interaction. Here, we show that this phosphorylation promotes the assembly of Munc18b-syntaxin 3-SNAP25 tripartite complex and membrane fusion machinery SNARE. Using siRNAs to screen for genes required for regulated epithelial secretion, we identified the requirements of CDK5 and Munc18b in cAMP-dependent gastric acid secretion. Biochemical characterization revealed that Munc18b bears a syntaxin 3-selective binding site located at its most C-terminal 53 amino acids. Significantly, the phosphorylation of Thr572 by CDK5 attenuates Munc18b-syntaxin 3 interaction and promotes formation of Munc18b-syntaxin 3-SNAP25 tripartite complex, leading to an assembly of functional Munc18b-syntaxin 3-SNAP25-VAMP2 membrane fusion machinery. Thus, our studies suggest a novel regulatory mechanism in which phosphorylation of Munc18b operates vesicle docking and fusion in regulated exocytosis.

Interactions of transmembrane carbonic anhydrase, CAIX, with bicarbonate transporters

Association of some plasma membrane bicarbonate transporters with carbonic anhydrase enzymes forms a bicarbonate transport metabolon to facilitate metabolic CO(2)-HCO(3)(-) conversions and coupled HCO(3)(-) transport. The transmembrane carbonic anhydrase, CAIX, with its extracellular catalytic site, is highly expressed in parietal and other cells of gastric mucosa, suggesting a role in acid secretion. We examined in transfected HEK293 cells the functional and physical interactions between CAIX and the parietal cell Cl(-)/HCO(3)(-) exchanger AE2 or the putative Cl(-)/HCO(3)(-) exchanger SLC26A7. Coexpression of CAIX increased AE2 transport activity by 28 +/- 7% and also activated transport mediated by AE1 and AE3 (32 +/- 10 and 37 +/- 9%, respectively). In contrast, despite a transport rate comparable to that of AE3, coexpressed CAIX did not alter transport associated with SLC26A7. The CAIX-associated increase of AE2 activity did not result from altered AE2 expression or cell surface processing. CAIX was coimmunoprecipitated with the coexpressed SLC4 polypeptides AE1, AE2, and AE3, but not with SLC26A7. GST pull-down assays with a series of domain-deleted forms of CAIX revealed that the catalytic domain of CAIX mediated interaction with AE2. AE2 and CAIX colocalized in human gastric mucosa, as indicated by coimmunofluorescence. This is the first example of a functional and physical interaction between a bicarbonate transporter and a transmembrane carbonic anhydrase. We conclude that CAIX can bind to some Cl(-)/HCO(3)(-) exchangers to form a bicarbonate transport metabolon.

The future of the pump

Since it was discovered 3 decades ago the H,K-ATPase has come to be recognized as the key both to the generation and pharmacologic suppression of gastric acid secretion. Although 30 years of concerted research has answered many questions, it is perhaps not surprising that these efforts have raised many new and crucial issues that await elucidation. These can be divided into 5 broad categories that relate to structure, mechanism, regulation, trafficking, and macromolecular interactions. It is probably safe to predict that the growing sophistication of x-ray crystallographic techniques will yield a picture of the pump's molecular structure in the near future. These insights will, in turn, illuminate the details of the process through which enzymatic hydrolysis is coupled to ion translocation with unprecedented clarity. The gastric parietal cell employs an extremely complicated system of receptors, kinases, and second messengers to maintain tight control over pump function. Upon activation, this cell also performs a massive and elegant membrane trafficking transformation that plays a critical role in the regulatory process. Finally, it is becoming clear that every ion transport protein is a component in a large macromolecular complex whose constituents help to determine all of the transport system's fundamental physiologic properties. These are the major topics that will drive H,K pump research in the future, and it is likely that their resolution will create the foundations for the next generation of therapies aimed at controlling gastric acid secretion and its clinical consequences.

The gastric H,K ATPase as a drug target: past, present, and future

The recent progress in therapy if acid disease has relied heavily on the performance of drugs targeted against the H,K ATPase of the stomach and the H2 receptor antagonists. It has become apparent in the last decade that the proton pump is the target that has the likelihood of being the most sustainable area of therapeutic application in the regulation of acid suppression. The process of activation of acid secretion requires a change in location of the ATPase from cytoplasmic tubules into the microvilli of the secretory canaliculus of the parietal cell. Stimulation of the resting parietal cell, with involvement of F-actin and ezrin does not use significant numbers of SNARE proteins, because their message is depleted in the pure parietal cell transcriptome. The cell morphology and gene expression suggest a tubule fusion-eversion event. As the active H,K ATPase requires efflux of KCl for activity we have, using the transcriptome derived from 99% pure parietal cells and immunocytochemistry, provided evidence that the KCl pathway is mediated by a KCQ1/KCNE2 complex for supplying K and CLIC6 for supplying the accompanying Cl. The pump has been modeled on the basis of the structures of different conformations of the sr Ca ATPase related to the catalytic cycle. These models use the effects of site directed mutations and identification of the binding domain of the K competitive acid pump antagonists or the defined site of binding for the covalent class of proton pump inhibitors. The pump undergoes conformational changes associated with phosphorylation to allow the ion binding site to change exposure from cytoplasmic to luminal exposure. We have been able to postulate that the very low gastric pH is achieved by lysine 791 motion extruding the hydronium ion bound to carboxylates in the middle of the membrane domain. These models also allow description of the K entry to form the K liganded form of the enzyme and the reformation of the ion site inward conformation thus relating the catalytic cycle of the pump to conformational models. The mechanism of action of the proton pump inhibitor class of drug is discussed along with the cysteines covalently bound with these inhibitors. The review concludes with a discussion of the mechanism of action and binding regions of a possible new class of drug for acid control, the K competitive acid pump antagonists.

Development of pancreatic acinar cell metaplasia after successful administration of omeprazole for 6 months in rats

Long-term use of proton pump inhibitors (PPIs) has been reported to worsen corpus atrophic gastritis in patients with Helicobacter pylori infection. On the other hand, PPIs have been associated with fundic gland-type gastric polyps and various histological changes. In the present study, we attempted to establish a protocol for omeprazole (OPZ) administration to rats over a longer period and examined the morphological changes in the gastric mucosa after administration of OPZ for 6 months. A total of 34 Wistar rats (8 weeks old) were used. In a preliminary experiment to determine the appropriate dose of OPZ, the rats had ad libitum access to food containing different doses of OPZ for 1 month. We found an approximate dose of 100 mg/kg body weight/day of OPZ to be most suitable from the point of view of intragastric pH, body weight, and serum gastrin level. In the experiment proper, rats were divided into two groups, either control or OPZ diets, and morphological changes in the gastric mucosa in each group were then examined by hematoxylin and eosin and immunohistochemical staining with alpha-amylase, trypsin, and chromogranin A. Multiple vacuolar degeneration of parietal cells and numerous small mucous cells were evident at 1 month after treatment with OPZ. At 6 months after treatment with OPZ, cystic degeneration and acinar-cell-like cells containing red granules positive for alpha-amylase and trypsin and negative for chromogranin A were detected in the OPZ rats. The serum gastrin level in the OPZ group was significantly higher than that in the control group. We have established a protocol for long-term administration of OPZ in rats that is a useful model for analyzing morphological changes after long-term PPI therapy. Long-term OPZ treatment causes hypergastrinemia and pancreatic acinar cell metaplasia in this animal model.

A continuous dietary supply of free calcium formate negatively affects the parietal cell population and gastric RNA expression for H+/K+-ATPase in weaning pigs

Baby formula acidification can be used to reduce diarrhea. Calcium formate is a dietary acidifier frequently used in animal weaning diets; it is also a source of available calcium. Gastric acidification reduces gastrin release and hydrochloric acid (HCl) secretion. To study the medium-term effects on fundic gastric mucosa, we fed weaning pigs control diets or diets supplemented with free or fat-protected calcium formate. We evaluated the following: 1) the number of HCl-secreting parietal cells, by immunohistochemistry using an antibody against H(+)/K(+)-ATPase; 2) the number of enteroendocrine cells immunohistochemically stained with chromogranin A (CGA), somatostatin, and histamine (HIS); and 3) the expression of the H(+)/K(+)-ATPase gene, by real-time RT-PCR in the oxyntic mucosa. Cells co-staining for CGA and HIS were defined as enterochromaffin-like (ECL) cells. Pigs fed calcium formate had fewer parietal cells and a lower expression of the H(+)/K(+)-ATPase gene than the controls (P < 0.05). This reduction did not occur in pigs fed fat-protected calcium formate. Somatostatin immune-reactive cells were also more numerous in pigs fed free calcium formate than in controls (P < 0.05). The number of ECL cells was not affected. Using covariance analysis, the number of parietal cells explained part of the differences in the expression of H(+)/K(+)-ATPase gene (positive correlation, r = 0.385, P < 0.01), and excluded the statistical significance of the diet. In the future, the effects on the oxyntic mucosa should be checked when the diet supplemented with calcium formate is discontinued. Furthermore, a reduction in the number of parietal cells could impair the absorption of vitamin B-12 due to a reduced secretion of the intrinsic factor by these cells.

The cryofixation of isolated rat gastric mucosa provides new insights into the functional transformation of gastric parietal cells: an in vitro experimental model study

Cryofixation is currently accepted as the best initial fixation step to preserve not only the fine structure but also the antigenicity of biological samples. To elucidate the functional transformation of gastric parietal cells, we have newly developed an in vitro experimental model, named the isolated gastric mucosa. In this study, acid secretion of the parietal cell was stimulated with histamine or inhibited with cimetidine, and the samples were cryofixed by plunge freezing for light microscopy or high-pressure freezing for electron microscopy. As a result, the organization of glandular cells was well-preserved and quite similar to freshly excised rat gastric mucosa for at least 2 h after isolation. Immunohistochemistry of H+/K+-ATPase demonstrated a translocation of H+/K+-ATPase from the cytoplasm to the apical membrane associated with histamine-stimulation. In cimetidine-treated mucosa, most of the parietal cells were morphologically in the resting state, showing numerous tubulovesicles in their cytoplasm. In contrast, histamine-stimulated parietal cells exhibited well-developed intracellular canaliculi lined with long microvilli. To the best of our knowledge, the present study is first to demonstrate an electron micrograph that strongly suggests a membrane fusion between the tubulovescile and the apical membrane. Moreover, a stimulation-associated translocation of ezrin was clearly shown from the cytoplasm to the apical region, corresponding to apical microvilli development in the isolated gastric mucosa model. We here describe the preparation of the isolated rat gastric mucosa model, which provides new insights into the functional transformation of parietal cells by the application of cryotechniques.

L-type amino acids stimulate gastric acid secretion by activation of the calcium-sensing receptor in parietal cells

Parietal cells are the primary acid secretory cells of the stomach. We have previously shown that activation of the calcium-sensing receptor (CaSR) by divalent (Ca(2+)) or trivalent (Gd(3+)) ions stimulates acid production in the absence of secretagogues by increasing H(+),K(+)-ATPase activity. When overexpressed in HEK-293 cells, the CaSR can be allosterically activated by L-amino acids in the presence of physiological concentrations of extracellular Ca(2+) (Ca(o)(2+); 1.5-2.5 mM). To determine whether the endogenously expressed parietal cell CaSR is allosterically activated by L-amino acids, we examined the effect of the amino acids L-phenylalanine (L-Phe), L-tryptophan, and L-leucine on acid secretion. In ex vivo whole stomach preparations, exposure to L-Phe resulted in gastric luminal pH significantly lower than controls. Studies using D-Phe (inactive isomer) failed to elicit a response on gastric pH. H(+)-K(+)-ATPase activity was monitored by measuring the intracellular pH (pH(i)) of individual parietal cells in isolated rat gastric glands and calculating the rate of H(+) extrusion. We demonstrated that increasing Ca(o)(2+) in the absence of secretagogues caused a dose-dependent increase in H(+) extrusion. These effects were amplified by the addition of amino acids at various Ca(o)(2+) concentrations. Blocking the histamine-2 receptor with cimetidine or inhibiting system L-amino acid transport with 2-amino-2-norbornane-carboxylic acid did not affect the rate of H(+) extrusion in the presence of L-Phe. These data support the conclusion that amino acids, in conjunction with a physiological Ca(o)(2+) concentration, can induce acid secretion independent of hormonal stimulation via allosteric activation of the stomach CaSR.

Immunolocalisation of bilitranslocase in mucosecretory and parietal cells of the rat gastric mucosa

Bilitranslocase is a plasma membrane carrier localised at the vascular pole of the rat liver cell, where it mediates uptake of organic anions from the blood into the liver. This carrier is also present in the epithelium of the rat gastric mucosa, with similar molecular mass and functional properties. An immunohistochemical study reveals that both the mucus-secreting cells of the gastric pit and the H+-secreting parietal cells express bilitranslocase. These data point to a possible role of bilitranslocase and of its food-borne substrates (anthocyanins and nicotinic acid) in regulating the function and the permeability of the gastric mucosa.

[Chronic EBV-infection in children with a high level of anti-H+/K+-ATPhase antibodies in gastric parietal]

We examined 50 children at the age of 4-17 suffering from chronic gastritis. AntiH+/K+-ATPhase antibodies of gastric parietal cells, anti-EBV antibodies IgG EA and IgM VCA were determined with the help of immune-enzyme analysis methods. The first group comprised 28 children with a high level of antiparietal antibodies in the blood serum, and 22 children with a normal level of antiparietal antibodies made up the second group. The HP identification was carried out for all children. Anti-EBV antibodies IgG EA were found in 72% of children, and there were no statistical differences in the frequency and level of antibodies IgG EA. IgM VCA were not found in any of the patients. However, HP-infection was revealed in 64.3% in the first group vs. 22.7% in the second group (p < 0,05); the combination of HB and chronic EBV infection was also more frequent in the first group than in the second group (42.8% and 18.1%, respectively, p < 0,05).

Gastric autoimmunity: the role of Helicobacter pylori and molecular mimicry

Pathogens can induce autoreactive T cells to initiate autoimmune disease by several mechanisms. Pathogen-induced inflammation results in the enhanced presentation of self antigens, which causes the expansion of the activated autoreactive T cells that are required for disease onset. Alternatively, a pathogen might express antigens with epitopes that are structurally similar to epitopes of autoantigens, resulting in a mechanism of molecular mimicry. This is the case for Helicobacter pylori-associated human autoimmune gastritis, in which the activated CD4+ Th1 cells that infiltrate the gastric mucosa cross-recognize the epitopes of self gastric parietal cell H(+)K(+)-ATPase and of various H. pylori proteins. Therefore, in genetically susceptible individuals, H. pylori infection can start or worsen gastric autoimmunity, leading to atrophic gastritis.

Estrogen-producing steroidogenic pathways in parietal cells of the rat gastric mucosa

Recently we demonstrated the presence of aromatase (P450(arom)), estrogen synthetase, and the active production of estrogen in parietal cells of the rat stomach. We therefore investigated the steroidogenic pathways of estrogen and also other steroid metabolites in the gastric mucosa of male rats, by showing the mRNA expression of steroidogenic enzymes using RT-PCR and in situ hybridization histochemistry, and by measuring the blood concentration of steroids in the artery and the portal vein. RT-PCR analysis showed the strong mRNA expression of 17alpha-hydroxylase/17,20-lyase (P450(17alpha)), 17beta-hydroxysteroid dehydrogenase (HSD) type III and P450(arom), and the weak mRNA expression of 17beta-HSD type II, 5alpha-reductase type I and 3alpha-HSD. The other mRNAs of steroidogenic enzymes examined were not detected. In situ hybridization histochemistry demonstrated the localization of mRNAs for P450(17alpha), 17beta-HSD type III and P450(arom) in the parietal cells. Higher levels of progesterone and testosterone were found in the artery compared with the portal vein. Higher amounts of estrone and 17beta-estradiol, by contrast, were present in the portal vein compared with the artery. These results indicate that parietal cells of rat stomach convert circulating progesterone and/through androstenedione and testosterone to synthesize both estrone and 17beta-estradiol, which then enter the liver via the portal vein.

High-pressure freezing of isolated gastric glands provides new insight into the fine structure and subcellular localization of H+/K+-ATPase in gastric parietal cells

High-pressure freezing (HPF) is currently the most reliable method to obtain an adequately frozen sample for high-resolution morphological evaluation. Here we applied the HPF technique to isolated rabbit gastric glands to reveal structural evidence that may be correlated with functional activity of gastric parietal cells. This approach provided well-preserved fine structure and excellent antigenicity of several parietal cell proteins. Microtubules were abundant in the cytoplasm and frequently appeared to be associating with tubulovesicles. Interestingly, many electron-dense coated vesicles were apparent around the intracellular canaliculi (IC) of resting parietal cells, consistent with active membrane retrieval from the apical membranes. Immunolabeling of H+/K+-ATPase was evident on the endocytic components (e.g., multivesicular bodies) and tubulovesicles. After histamine stimulation, the parietal cells characteristically showed expanded IC membranes with varied features of their apical microvilli. The labeling density of H+/K+-ATPase was four-fold higher on the IC membrane of stimulated parietal cells than on that of resting parietal cells. Immunolabeling of ezrin was clearly identified on the IC and basolateral membranes of parietal cells, corresponding to their F-actin-rich sites. The present findings provide a new insight into the correlation of cell structure and function in gastric parietal cells.

TNF-alpha induces apoptosis of parietal cells

Helicobacter pylori infection can be associated with chronic gastric inflammation and hypochlorhydria with increased levels of the proinflammatory cytokines. The current study investigated the effects of TNF-alpha on programmed death of gastric parietal cells. TNF-alpha induced apoptosis of parietal cells in isolated perfused rat stomachs at 10ng/mL. In isolated and highly enriched rat parietal cells, 10ng/mL TNF-alpha induced a 2.6-fold increase in the apoptotic rate. The 55kDa protein of TNFR-1 but not the 75kDa of TNFR-2 was detected by Western blot analysis. TNF-alpha-induced apoptosis of isolated parietal cells was inhibited by pretreatment with different NF-kappaB-inhibitors, nitric oxide synthase inhibitors and with antisense-oligodeoxynucleotides against the p65 subunit of NF-kappaB. Investigation of downstream signaling pathways of apoptosis revealed that TNF-alpha induced the expression of iNOS, but failed to stimulate the activity of caspase 3. The TNF-alpha effect on gastric parietal cells may contribute to the atrophy and hypochlorhydria of the gastric mucosa observed during chronic H. pylori infection.

Direct activation of gastric H,K-ATPase by N-terminal protein kinase C phosphorylation. Comparison of the acute regulation mechanisms of H,K-ATPase and Na,K-ATPase

In this study we compared the protein kinase dependent regulation of gastric H,K-ATPase and Na,K-ATPase. The protein kinase A/protein kinase C (PKA/PKC) phosphorylation profile of H,K-ATPase was very similar to the one found in the Na,K-ATPase. PKC phosphorylation was taking place in the N-terminal part of the alpha-subunit with a stoichiometry of approximately 0.6 mol Pi/mole alpha-subunit. PKA phosphorylation was in the C-terminal part and required detergent, as is also found for the Na,K-ATPase. The stoichiometry of PKA-induced phosphorylation was approximately 0.7 mol Pi/mole alpha-subunit. Controlled proteolysis of the N-terminus abolished PKC phosphorylation of native H,K-ATPase. However, after detergent treatment additional C-terminal PKC sites became exposed located at the beginning of the M5M6 hairpin and at the cytoplasmic L89 loop close to the inner face of the plasma membrane. N-terminal PKC phosphorylation of native H,K-ATPase alpha-subunit was found to stimulate the maximal enzyme activity by 40-80% at saturating ATP, depending on pH. Thus, a direct modulation of enzyme activity by PKC phosphorylation could be demonstrated that may be additional to the well-known regulation of acid secretion by recruitment of H,K-ATPase to the apical membranes of the parietal cells. Moreover, a distinct difference in the regulation of H,K-ATPase and Na,K-ATPase is the apparent absence of any small regulatory proteins associated with the H,K-ATPase.

[Submicroscopic aspects of the mechanism of inhibitors of H+/K+-ATPase in gastric parietal cells]

In most developed countries of the world the basis of the ulcer treatment is formed by H+/K(+)-ATPase blockers: omeprazole, pantoprazole, lansoprazole etc. though in accordance with the Maastricht treaty (2) the first line therapy may also be based upon the application of one of H2-histamine receptor blockers, specifically the two-component ranitidine bismuth citrate preparation.

The unique ultrastructure of secretory membranes in gastric parietal cells depends upon the presence of H+, K+ -ATPase

Ion transporters play a central role in gastric acid secretion. To determine whether some of these transporters are necessary for the normal ultrastructure of secretory membranes in gastric parietal cells, mice lacking transporters for H+, K+, Cl-, and Na+ were examined for alterations in volume density (Vd) of basolateral, apical, tubulovesicular and canalicular membranes, microvillar dimensions, membrane flexibility, and ultrastructure. In mice lacking Na+/H+ exchanger 1 (NHE1) or the Na+-K+-2Cl- cotransporter (NKCC1), the ultrastructure and Vd of secretory membranes and the secretory canalicular to tubulovesicular membrane ratio (SC/TV), a morphological correlate of secretory activity, were similar to those of wild-type mice. In mice lacking Na+/H+ exchanger 2 (NHE2) or gastric H+, K+ -ATPase alpha- or beta-subunits, the SC/TV ratio and Vd of secretory membranes were decreased, though canaliculi were often dilated. In H+, K+ -ATPase-deficient parietal cells, canalicular folds were decreased, normally abundant tubulovesicles were replaced with a few rigid round vesicles, and microvilli were sparse, stiff and short, in contrast to the long and flexible microvilli in wild-type cells. In addition, microvilli of the H+, K+ -ATPase-deficient parietal cells had centrally bundled F-actin filaments, unlike the microvilli of wild-type cells, in which actin filaments were peripherally positioned concentric to the plasmalemma. Data showed that the absence of H+, K+ -ATPase produced fundamental changes in parietal cell membrane ultrastructure, suggesting that the pump provides an essential link between the membranes and F-actin, critical to the gross architecture and suppleness of the secretory membranes.

Different actions of protein kinase C isoforms alpha and epsilon on gastric acid secretion

1. The phorbol ester TPA, an activator of protein kinase C (PKC), inhibits cholinergic stimulation of gastric acid secretion but increases basal H(+) secretion. 2. Since these contradictory findings suggest the action of different PKC isozymes we analysed the role of calcium-dependent PKC-alpha, and calcium-independent PKC-epsilon in gastric acid secretion. 3. Inhibition of PKC-alpha by the indolocarbazole Gö 6976 revealed that about 28% of carbachol-induced acid secretion was inhibited by PKC-alpha. In the presence of Gö 6976 approximately 64% of the carbachol-induced signal transduction is mediated by Ca(2+)/calmodulin-dependent protein kinase II (CaMKII), and 14% is conveyed by PKC-epsilon as deduced from the inhibition with the bisindolylmaleimide Ro 31-8220. 4. Inhibition of carbachol-induced acid secretion by TPA was accompanied by a decrease in CaMKII activity. 5. The stimulation of basal acid secretion by TPA was biphasic with a peak at a very low concentration (10 pM), resulting in an activation of the calcium-sensor CaMKII. The activation was determined with a phosphospecific polyclonal antibody against active CaMKII. The TPA-induced increase of H(+) secretion was sensitive to the cell-permeable Ca(2+)-chelator BAPTA/AM, Ro 31-8220, and the CaMKII-inhibitor KN-62, but not to Gö 6976. 6. Since TPA induced the translocation of PKC-epsilon but not of PKC-alpha in resting parietal cells, PKC-epsilon seems to be at least responsible for an initial elevation of free intracellular calcium to initiate TPA-induced acid secretion. 7. Our data indicate the different roles of two PKC isoforms: PKC-epsilon activation appears to facilitate cholinergic stimulation of H(+)-secretion likely by increasing intracellular calcium. In contrast, PKC-alpha activation attenuates acid secretion accompanied by a down-regulation of CaMKII activity.

Regulation and function of COX-2 gene expression in isolated gastric parietal cells

We examined expression, function, and regulation of the cyclooxygenase (COX)-2 gene in gastric parietal cells. COX-2-specific mRNA was isolated from purified (>95%) canine gastric parietal cells in primary culture and measured by Northern blots using a human COX-2 cDNA probe. Carbachol was the most potent inducer of COX-2 gene expression. Gastrin and histamine exhibited minor stimulatory effects. Carbachol-stimulated expression was inhibited by intracellular Ca(2+) chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-AM (90%), protein kinase C (PKC) inhibitor GF-109203X (48%), and p38 kinase inhibitor SB-203580 (48%). Nuclear factor (NF)-kappaB inhibitor 1-pyrrolidinecarbodithioic acid inhibited carbachol-stimulated expression by 80%. Similar results were observed in the presence of adenoviral vector Ad.dom.neg.IkappaB, which expresses a repressor of NF-kappaB. Addition of SB-203580 with Ad.dom.neg.IkappaB almost completely blocked carbachol stimulation of COX-2 gene expression. We examined the effect of carbachol on PGE(2) release by enzyme-linked immunoassay. Carbachol induced PGE(2) release. Ad.dom.neg.IkappaB, alone or with SB-203580, produced, respectively, partial (70%) and almost complete (>80%) inhibition of carbachol-stimulated PGE(2) production. Selective COX-2 inhibitor NS-398 blocked carbachol-stimulated PGE(2) release without affecting basal PGE(2) production. In contrast, indomethacin inhibited both basal and carbachol-stimulated PGE(2) release. Carbachol induces COX-2 gene expression in the parietal cells through signaling pathways that involve intracellular Ca(2+), PKC, p38 kinase, and activation of NF-kappaB. The functional significance of these effects seems to be stimulation of PGE(2) release.

Proton pump activation in stimulated parietal cells is regulated by gastric acid secretory capacity: a human study

Under normal physiological conditions, gastric acid production is controlled by a negative feedback mechanism. Proton pump inhibitors, such as pantoprazole, inhibit gastric acid secretion by irreversibly binding and inactivating luminally active hydrogen potassium ATPase. Recovery of acid production after treatment with a proton pump inhibitor is driven by new pump synthesis, activation of existing cytoplasmic pumps, or reversal of proton pump inhibition. The authors measured the time course of the inhibition and recovery of acid secretion in healthy volunteers following intravenous administration of pantoprazole to determine the rate of proton pump activation under maximally stimulated conditions. Gastric acid production was measured in 27 Helicobacter pylori negative healthy volunteers (mean age = 31 +/- 7 years; 17 men, 10 women) who received single doses of intravenous pantoprazole (20, 40, 80, or 120 mg) in the presence of a continuous intravenous infusion of 1 ug/kg/h of pentagastrin. From the time profile of acid secretion, the authors described the rate of change of acid output using an irreversible pharmacodynamic response model represented by the equation dR/dt = -k x R x Cpanto + Ln2/PPR x (Ro-R) and correlated the parameter values with demographic factors and gastric acid measurements. Mean stimulated acid output secretion was 21.6 +/- 18.4 mEq/h (range: 1.6-90.5) prior to the administration of pantoprazole and remained steady for 25 hours after placebo administration. Intravenous pantoprazole inhibited acid output in a dose-response fashion, with maximal inhibition (99.9%) occurring after an 80 mg dose. Mean proton pump recovery time was 37.1 +/- 21.0 hours (range: 6.7-75), and recovery was independent of the dose of pantoprazole. There was no association noted between proton pump recovery time and gender, age, race, body weight, or pantoprazole dose. However, there was an inverse correlation between acid output during baseline stimulation and recovery of acid secretion. Mean proton pump recovery time in stimulated normal human volunteers was 37.1 +/- 21.0 hours, with a range of 6.7 to 75 hours. The authors hypothesize that there may be a normal homeostatic mechanism that maintains acid secretory capability within a normal range by altering the rate of proton pump activation dependent on the individual's parietal cell mass. Abnormalities of this process may be responsible for the development of acid peptic disease in susceptible individuals.

CaMKII is activated and translocated to the secretory apical membrane during cholinergically conveyed gastric acid secretion

The Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) is thought to be activated during the cholinergic stimulation of gastric acid secretion. The carbachol-induced acid production of cultured rabbit parietal cells was dose-dependently inhibited by the CaMKII inhibitor KN-62 as measured by accumulation of the weak base [(14)C]aminopyrine ([(14)C]-AP). Inhibition by KN-62 was most efficient at concentrations of carbachol >10(-6) M. After carbachol stimulation, we observed an activation of CaMKII activity, and its translocation to the apical membrane of gastric mucosal cells. We found a doubling of the abundance of CaMKII to the stimulus-associated apical membrane (SA vesicles) compared to the apical membrane from the resting state after carbachol induction. This was shown by both an anti-CaMKII serum and the 1.8-fold increase of the CaMKII phosphotransferase activity in vitro. The SA vesicles exhibited a strong increase of autoactivated CaMKII probed with an anti-autoactivated CaMKII antibody. Additionally, we observed a colocalization of both CaMKII and the H(+)-K(+)-ATPase of SA vesicles similar to the colocalization of both enzymes to the tubulovesicles suggesting them as at least one pool for the SA vesicular CaMKII. Our data indicate that the activation of CaMKII and the carbachol-dependent redistribution of CaMKII to the SA vesicles are distinct processes that occur in parallel to regulate the activity and localization of CaMKII. These findings contribute to the model implicating an involvement for CaMKII in the intracellular dynamics of the acid secretion.

Extracellular signal-regulated protein kinases mediate H(+),K(+)-ATPase alpha-subunit gene expression

Extracellular signal-regulated protein kinases (ERKs) are important in many cellular functions. We and others have previously reported that prolonged exposure of gastric parietal cells to epidermal growth factor (EGF) enhanced gastric acid secretion stimulated by secretagogues via ERKs. In this study, we examined whether ERKs regulated H(+),K(+)-ATPase alpha-subunit gene expression using a gastric cancer cell line, AGS. EGF induced ERK activity time- and dose-dependently with a maximal effect observed at 10 min and 10 nM, respectively. The MEK inhibitors, U0126 and PD-98059, dose-dependently inhibited the ERK activity stimulated by EGF. To test H(+),K(+)-ATPase alpha-subunit gene expression, we transfected AGS cells with a plasmid containing a canine H(+),K(+)-ATPase alpha-subunit gene promoter fused to a luciferase reporter gene. EGF induced luciferase activity in transfected cells; this effect was inhibited by the MEK inhibitors, suggesting that EGF-induced gene expression involved the ERK pathway. When AGS cells were transfected with the reporter plasmids in conjunction with an expression vector encoding constitutively active MEK1, luciferase activity was strongly enhanced; this effect was attenuated by the MEK inhibitors or by an additional cotransfection of dominant negative MEK1. Taken together, our results led us to conclude that the ERK pathway may mediate H(+),K(+)-ATPase alpha-subunit gene expression, contributing to gastric acid secretion in parietal cells.

Functional role of protein kinase B/Akt in gastric acid secretion

Epidermal growth factor (EGF) stimulates gastric acid secretion and H(+)/K(+)-ATPase alpha-subunit gene expression. Because EGF activates the serine-threonine protein kinase Akt, we explored the role of Akt in gastric acid secretion. Akt phosphorylation and activation were measured by kinase assays and by Western blots with an anti-phospho-Akt antibody, using lysates of purified (>95%) canine gastric parietal cells in primary culture. EGF induced Akt phosphorylation and activation, whereas carbachol had no effect. LY294002, an inhibitor of phosphoinositide 3-kinase, completely blocked EGF induction of Akt phosphorylation, whereas the MEK1 inhibitor PD98059 and the protein kinase C inhibitor GF109203X had no effect. We examined the role of Akt in H(+)/K(+)-ATPase gene expression by Northern blotting using a canine H(+)/K(+)-ATPase alpha-subunit cDNA probe. The parietal cells were transduced with a multiplicity of infection of 100 of the adenoviral vector Ad.Myr-Akt, which overexpresses a constitutively active Akt gene, or with the control vector Ad.CMV-beta-gal, which expresses beta-galactosidase. Ad.Myr-Akt induced H(+)/K(+)-ATPase alpha-subunit gene expression 3-fold, whereas it failed to stimulate the gene cyclooxygenase-2, which was potently induced by carbachol in the same parietal cells. Ad.Myr-Akt induced aminopyrine uptake 4-fold, and it potentiated the stimulatory action of carbachol 3-fold. In contrast, Ad.Myr-Akt failed to induce changes in either parietal cell actin content, measured by Western blots with an anti-actin antibody or in the organization of the actin cellular cytoskeleton, visualized by fluorescein phalloidin staining and confocal microscopy. Transduction of the parietal cells with a multiplicity of infection of 100 of the adenoviral vector Ad.dom.neg.Akt, which overexpresses an inhibitor of Akt, blocked the stimulatory effect of EGF on both aminopyrine uptake and H(+)/K(+)-ATPase production, measured by Western blots with an anti-H(+)/K(+)-ATPase alpha-subunit antibody. Thus, EGF induces a cascade of events in the parietal cells that results in the activation of Akt. The functional role of Akt appears to be stimulation of gastric acid secretion through induction of H(+)/K(+)-ATPase expression.

Morphological support for paracrine inhibition of gastric acid secretion by nitric oxide in humans

BACKGROUND

Functional studies have shown that nitric oxide (NO) inhibits gastric acid secretion in a variety of species, including man. We have performed a morphological study with the intention of localizing the endothelial NO synthase (eNOS) in the human gastric mucosa.

METHODS

Fifteen healthy subjects voluntarily participated in the study, and mucosal biopsies were obtained from the cardia, corpus and antrum. The presence and localization of eNOS were studied using immunohistochemical techniques.

RESULTS

eNOS-immunoreactivity (eNOS-IR) is found in surface mucous cells of cardia, corpus and antrum. Unique to the oxyntic mucosa is the presence of eNOS-IR in 'endocrine-like' cells, found in close contact with parietal cells.

CONCLUSIONS

eNOS-IR cells in close apposition to parietal cells provide morphological support for paracrine inhibition of gastric acid secretion by NO.

Neuronal nitric oxide synthase: expression in rat parietal cells

Nitric oxide synthases (NOS) are enzymes that catalyze the generation of nitric oxide (NO) from L-arginine and require nicotinamide adenine dinucleotide phosphate (NADPH) as a cofactor. At least three isoforms of NOS have been identified: neuronal NOS (nNOS or NOS I), inducible NOS (iNOS or NOS II), and endothelial NOS (eNOS or NOS II). Recent studies implicate NO in the regulation of gastric acid secretion. The aim of the present study was to localize the cellular distribution and characterize the isoform of NOS present in oxyntic mucosa. Oxyntic mucosal segments from rat stomach were stained by the NADPH-diaphorase reaction and with isoform-specific NOS antibodies. The expression of NOS in isolated, highly enriched (>98%) rat parietal cells was examined by immunohistochemistry, Western blot analysis, and RT-PCR. In oxyntic mucosa, histochemical staining revealed NADPH-diaphorase and nNOS immunoreactivity in cells in the midportion of the glands, which were identified as parietal cells in hematoxylin and eosin-stained step sections. In isolated parietal cells, decisive evidence for nNOS expression was obtained by specific immunohistochemistry, Western blotting, and RT-PCR. Cloning and sequence analysis of the PCR product confirmed it to be nNOS (100% identity). Expression of nNOS in parietal cells suggests that endogenous NO, acting as an intracellular signaling molecule, may participate in the regulation of gastric acid secretion.

Protein kinase C gene expression in dispersed guinea-pig gastric parietal cells

BACKGROUND AIMS

It has been implicated that protein kinase C (PKC) is involved in gastric acid secretion. The purpose of this study is to examine whether mRNA expression of PKC isoforms is observed in guinea-pig gastric parietal cells, and whether such PKC expression is regulated by agonists that stimulate gastric acid secretion.

METHODS

Expression of PKC mRNA was assessed using isolated guinea-pig gastric parietal cells treated with or without three kinds of agonists by Northern blot analysis.

RESULTS

(1) alpha, gamma and zetaPKC mRNAs were expressed in guinea-pig gastric parietal cells; (2) both carbachol and gastrin increased the level of alpha and gammaPKC mRNAs, but synthesis of zetaPKC mRNA was not affected by these agonists, and (3) histamine did not affect the expression level of alpha, gamma and zetaPKC mRNAs.

CONCLUSION

alpha and gammaPKC isoforms may be involved in the regulation of gastric acid secretion.

Differentiation of mucous neck cells into parietal cells: a new concept of mitochondrial biogenesis

Parietal cells of the gastric fundic mucosa are small and contain only a few tiny mitochondria when they begin to differentiate from mucous neck cells. The canalicular ATPase activity characteristic of mature parietal cells is discrete in these young cells, whereas areas of very high activity are apparent in the Golgi complex, reticulum, nuclear envelope, mitochondrial wall, and plasma membrane. Close relations and contacts occur between mitochondria and these organelles, and the size and number of mitochondria increase progressively. These relations, as well as mitochondrial ATPase activity (a true differentiation marker), cease once the mitochondria become as numerous and large as those of a mature parietal cell. Our observations suggest that a secondary form of mitochondrial biogenesis, involving the massive participation of other organelles and independent of the classical mechanisms inherent in mitosis, occurs in parietal cells at the beginning of G1 phase during the 6 days of their maturation.

Localization of matrix metalloproteinases and tissue inhibitor of metalloproteinases-2 in normal human and rabbit stomachs

BACKGROUND/AIMS

Matrix metalloproteinases (MMPs) are endopeptidases that degrade extracellular matrix and are involved in the pathogenesis of gastrointestinal ulcer and cancer along with tissue inhibitors of metalloproteinases (TIMPs). The purpose of this study is to examine their localization and functions in the normal stomach.

METHODS

We examined the localization of MMP-1, MMP-2, MMP-9 and TIMP-2 in normal human and rabbit stomachs by light- and electron-microscopic immunohistochemistry and Western blotting, and the enzymatic activities of MMP-2 and MMP-9 by gelatin zymography.

RESULTS

Immunohistochemistry revealed their localization in parietal cells, and surface and foveolar epithelial cells. Electron-microscopic immunohistochemistry of parietal cells showed immunolabeling of MMP-2 and TIMP-2 in the cisternae of the rough endoplasmic reticulum, and that of MMP-1 and MMP-9 in tubular structures in their cytoplasm. Western blotting revealed that the densities of MMP-2 and MMP-9 bands were higher for the fundic gland region than for the pyloric gland region. Gelatin zymography revealed that tissue extracts of the fundic gland region exhibited higher enzymatic activity of MMP-2 and MMP-9 than those of the pyloric gland region.

CONCLUSION

Normal rabbit and human stomachs contain MMP-1, MMP-2, MMP-9, and TIMP-2 and these are mainly localized in, and synthesized by parietal cells.

Gastric acid secretion in aquaporin-4 knockout mice

The aquaporin-4 (AQP4) water channel has been proposed to play a role in gastric acid secretion. Immunocytochemistry using anti-AQP4 antibodies showed strong AQP4 protein expression at the basolateral membrane of gastric parietal cells in wild-type (+/+) mice. AQP4 involvement in gastric acid secretion was studied using transgenic null (-/-) mice deficient in AQP4 protein. -/- Mice had grossly normal growth and appearance and showed no differences in gastric morphology by light microscopy. Gastric acid secretion was measured in anesthetized mice in which the stomach was luminally perfused (0. 3 ml/min) with 0.9% NaCl containing [(14)C]polyethylene glycol ([(14)C]PEG) as a volume marker. Collected effluent was assayed for titratable acid content and [(14)C]PEG radioactivity. After 45-min baseline perfusion, acid secretion was stimulated by pentagastrin (200 microg. kg(-1). h(-1) iv) for 1 h or histamine (0.23 mg/kg iv) + intraluminal carbachol (20 mg/l). Baseline gastric acid secretion (means +/- SE, n = 25) was 0.06 +/- 0.03 and 0.03 +/- 0.02 microeq/15 min in +/+ and -/- mice, respectively. Pentagastrin-stimulated acid secretion was 0.59 +/- 0.14 and 0.70 +/- 0.15 microeq/15 min in +/+ and -/- mice, respectively. Histamine plus carbachol-stimulated acid secretion was 7.0 +/- 1.9 and 8.0 +/- 1.8 microeq/15 min in +/+ and -/- mice, respectively. In addition, AQP4 deletion did not affect gastric fluid secretion, gastric pH, or fasting serum gastrin concentrations. These results provide direct evidence against a role of AQP4 in gastric acid secretion.

CGRP modulates mucin synthesis in surface mucus cells of rat gastric oxyntic mucosa

We examined the effects of the calcitonin gene-related peptide (CGRP), including the possible participation of nitric oxide (NO), on mucin biosynthesis in the surface epithelium and remaining deep mucosa as well as the entire mucosa and compared the distribution of CGRP and NO synthase (NOS) using a combination of double immunofluorescence labeling and multiple dye filter. Pieces of tissue obtained from the corpus and antrum were incubated in a medium containing [(3)H]glucosamine and CGRP, with or without the NOS inhibitor. CGRP dose-dependently enhanced [(3)H]glucosamine incorporation into the corpus mucin but had no effect on antral mucin biosynthesis. The CGRP receptor antagonist, CGRP-(8-37), prevented the increase in (3)H-labeled corpus mucin. This stimulation of corpus mucin synthesis disappeared after removal of the surface mucus cell layer. CGRP activated the mucin biosynthesis in the surface mucus cells. In the full-thickness corpus mucosa, CGRP-induced activation was completely blocked by the NOS inhibitor. CGRP-immunoreactive fibers were intertwined within the surface mucus cell layer with type I NOS immunoreactivity. These results show that CGRP-stimulated mucin biosynthesis mediated by NO is limited to surface mucus cells of the rat gastric oxyntic mucosa.

Agonist-induced cytoplasmic volume changes in cultured rabbit parietal cells

Concomitant Na(+)/H(+) and Cl(-)/HCO(3)(-) exchange activation occurs during stimulation of acid secretion in cultured rabbit parietal cells, possibly related to a necessity for volume regulation during the secretory process. We investigated whether cytoplasmic volume changes occur during secretagogue stimulation of cultured rabbit parietal cells. Cells were loaded with the fluorescent dye calcein, and the calcein concentration within a defined cytoplasmic volume was recorded by confocal microscopy. Forskolin at 10(-5) M, carbachol at 10(-4) M, and hyperosmolarity (400 mosmol) resulted in a rapid increase in the cytoplasmic dye concentration by 21 +/- 6, 9 +/- 4, and 23 +/- 5%, respectively, indicative of cell shrinkage, followed by recovery to baseline within several minutes, indicative of regulatory volume increase (RVI). Depolarization by 5 mM barium resulted in a decrease of the cytoplasmic dye concentration by 10 +/- 2%, indicative of cell swelling, with recovery within 15 min, and completely prevented forskolin- or carbachol-induced cytoplasmic shrinkage. Na(+)/H(+) exchange inhibitors slightly reduced the initial cell shrinkage and significantly slowed the RVI, whereas 100 microM bumetanide had no significant effect on either parameter. We conclude that acid secretagoguges induce a rapid loss of parietal cell cytoplasmic volume, followed by RVI, which is predominantly mediated by Na(+)/H(+) and Cl(-)/HCO(3)(-) exchange.

Reversible drug-induced oxyntic atrophy in rats

BACKGROUND & AIMS

Oxyntic atrophy is the hallmark of chronic gastritis. Many studies have sought to develop animal models for oxyntic atrophy, but none of them are reversible. We now report that rats administered high doses of DMP 777 demonstrate reversible oxyntic atrophy.

METHODS

DMP 777 was administered to CD-1 rats by oral gavage (200 mg. kg(-1). day(-1)). Serum gastrin level, in vivo acid secretion, and gastric histological changes were evaluated in DMP 777-dosed animals. Direct effects of DMP 777 on parietal cells were evaluated by assessment of aminopyrine accumulation into isolated rabbit parietal cells, as well as by assessment of DMP 777 effects on acridine orange fluorescence and H(+),K(+)-adenosine triphosphatase (ATPase) activity in isolated tubulovesicles.

RESULTS

Oral dosing with DMP 777 caused a rapid increase in serum gastrin levels and severe hypochlorhydria. DMP 777 inhibited aminopyrine accumulation into rabbit parietal cells stimulated with either histamine or forskolin. DMP 777 reversed a stimulated proton gradient in isolated parietal cell tubulovesicles. Oral dosing with DMP 777 led to rapid loss of parietal cells from the gastric mucosa. In response to the acute loss of parietal cells, there was an increase in the activity of the progenitor zone along with rapid expansion of the foveolar cell compartment. DMP 777 treatment also led to the emergence of bromodeoxyuridine-labeled cells and cells positive for periodic acid-Schiff in the basal region of fundic glands. With extended dosing over 3-6 months, foveolar hyperplasia and oxyntic atrophy were sustained while chief cell, enterochromaffin-like cell, and somatostatin cell populations were decreased. No histological evidence of neoplastic transformation was observed with dosing up to 6 months. Withdrawal of the drug after 3 or 6 months of dosing led to complete restitution of the normal mucosal lineages within 3 months.

CONCLUSIONS

DMP 777 acts as a protonophore with specificity for parietal cell acid-secretory membranes. DMP 777 in high doses leads to the specific loss of parietal cells. Foveolar hyperplasia, loss of normal gland lineages, and the emergence of basal mucous cells appear as sequelae of the absence of parietal cells. The results suggest that parietal cells are critical for the maintenance of the normal mucosal lineage repertoire.

Interaction of alpha- and beta-subunits in native H-K-ATPase and cultured cells transfected with H-K-ATPase beta-subunit

The assembly of the beta-subunit of the gastric H-K-ATPase (HKbeta) with the alpha-subunit of the H-K-ATPase or the Na-K-ATPase (NaKalpha) was characterized with two anti-HKbeta monoclonal antibodies (MAbs). In fixed gastric oxyntic cells, in H-K-ATPase in vitro, and in Madin-Darby canine kidney (MDCK) cells transfected with HKbeta, MAb 2/2E6 was observed to bind to HKbeta only when interactions between alpha- and beta-subunits were disrupted by various denaturants. The epitope for MAb 2/2E6 was mapped to the tetrapeptide S(226)LHY(229) of the extracellular domain of HKbeta. The epitope for MAb 2G11 was mapped to the eight NH(2)-terminal amino acids of the cytoplasmic domain of HKbeta. In transfected MDCK cells, MAb 2G11 could immunoprecipitate HKbeta with alpha-subunits of the endogenous cell surface NaKalpha, as well as that from early in the biosynthetic pathway, whereas MAb 2/2E6 immunoprecipitated only a cohort of unassembled endoglycosidase H-sensitive HKbeta. In HKbeta-transfected LLC-PK(1) cells, significant immunofluorescent labeling of HKbeta at the cell surface could be detected without postfixation denaturation or in live cells, although a fraction of transfected HKbeta could also be coimmunoprecipitated with NaKalpha. Thus assembly of HKbeta with NaKalpha does not appear to be a stringent requirement for cell surface delivery of HKbeta in LLC-PK(1) cells but may be required in MDCK cells. In addition, endogenous posttranslational regulatory mechanisms to prevent hybrid alpha-beta heterodimer assembly appear to be compromised in transfected cultured renal epithelial cells. Finally, the extracellular epitope for assembly-sensitive MAb 2/2E6 may represent a region of HKbeta that is associated with alpha-beta interaction.

A transmembrane segment determines the steady-state localization of an ion-transporting adenosine triphosphatase

The H,K-adenosine triphosphatase (ATPase) of gastric parietal cells is targeted to a regulated membrane compartment that fuses with the apical plasma membrane in response to secretagogue stimulation. Previous work has demonstrated that the alpha subunit of the H, K-ATPase encodes localization information responsible for this pump's apical distribution, whereas the beta subunit carries the signal responsible for the cessation of acid secretion through the retrieval of the pump from the surface to the regulated intracellular compartment. By analyzing the sorting behaviors of a number of chimeric pumps composed of complementary portions of the H, K-ATPase alpha subunit and the highly homologous Na,K-ATPase alpha subunit, we have identified a portion of the gastric H,K-ATPase, which is sufficient to redirect the normally basolateral Na,K-ATPase to the apical surface in transfected epithelial cells. This motif resides within the fourth of the H,K-ATPase alpha subunit's ten predicted transmembrane domains. Although interactions with glycosphingolipid-rich membrane domains have been proposed to play an important role in the targeting of several apical membrane proteins, the apically located chimeras are not found in detergent-insoluble complexes, which are typically enriched in glycosphingolipids. Furthermore, a chimera incorporating the Na, K-ATPase alpha subunit fourth transmembrane domain is apically targeted when both of its flanking sequences derive from H,K-ATPase sequence. These results provide the identification of a defined apical localization signal in a polytopic membrane transport protein, and suggest that this signal functions through conformational interactions between the fourth transmembrane spanning segment and its surrounding sequence domains.

Pentagalloylglucose, an antisecretory component of Paeoniae radix, inhibits gastric H+, K(+)-ATPase

We purified a compound with strong inhibitory effect on H+, K(+)-ATPase from Paeoniae radix, which has been used in Japan for the treatment of gastritis and peptic ulcers. The compound was identified as 1,2,3,4,6,-penta-o-galloyl-beta-D-glucose by proton nuclear magnetic resonance, carbon-13 nuclear magnetic resonance, and fast atomic bombardment mass spectrometry. The IC50 of the compound for H+, K(+)-ATPase was 166 nmol/l. Kinetic analyses indicated that the inhibition of the enzyme by pentagalloylglucose was noncompetitive with respect to K+. Pentagalloylglucose had relatively weak inhibitory effects for Mg(+)-ATPase (IC50: > 10 mumol/l) and Na+, K(+)-ATPase (IC50: 2.7 mumol/l). Pentagalloylglucose also inhibited the accumulation of [14C]aminopyrine in parietal cells that had been isolated from guinea pig stomach and stimulated by 10 mumol/l histamine (IC50: 7.8 mumol/l) and 1 mmol/l dbc-AMP (IC50: 10 mumol/l). These results suggest that pentagalloylglucose is a potent inhibitor of H+, K(+)-ATPase and may be responsible for inhibition of acid secretion by Paeoniae radix.

Inhibitory effect of sorbin on pepsin secretion in conscious cats and rabbits

Sorbin, a 153 amino acid polypeptide isolated from porcine upper small intestine and its shortest synthetic derivative, the C-terminal heptapeptide (C7-sorbin), substituted by D alaninamide in the last position (D7-sorbin), have proabsorptive and antisecretory effect in the different parts of the intestine. We showed that labeled C7-sorbin accumulated not only in the enterocytes and the enteric nervous system but also in the gastric chief cells in the rat. The chief cell secretion of pepsin was then studied in two other species, the cat and the rabbit, simultaneously with the acid secretion of parietal cells. Lipase secretion was studied in the rabbit because lipase is exclusively secreted by the upper cells of the fundic glands, which do not secrete pepsin. The animals were equipped with a gastric fistula, fully innervated, and a Heidenhain pouch, vagally denervated, during a continuous perfusion of pentagastrin (PG) 2 microg/kg. h and vasoactive intestinal peptide (VIP) 4 microg/kg. h. D7-sorbin (100 pmol/kg. h) inhibited cat and rabbit pepsin secretion from the innervated gastric fistula secretion and from the cat denervated Heidenhain pouc secretion, but was without effect on acid secretion and lipase secretion. These data indicate that the inhibitory effect of sorbin is specific on chief cells because the acid parietal cell secretion in both species and lipase upper cell secretion of the fundic glands, in the rabbit, are not implicated.

Regulation and function of p38 protein kinase in isolated canine gastric parietal cells

We examined the regulation and functional role of p38 kinase in gastric acid secretion. p38 kinase was immunoprecipitated from cell lysates of highly purified gastric parietal cells in primary culture, and its activity was quantitated by in vitro kinase assay. Carbachol effects were dose- and time-dependent, with a maximal 10-fold stimulatory effect detected after 30 min of incubation. SB-203580, a highly selective inhibitor of p38 kinase, blocked carbachol induction of p38 kinase activity, with maximal inhibition at 10 microM. Stimulation by carbachol was unaffected by preincubation of parietal cells with the intracellular Ca(2+) chelator BAPTA-AM, but incubation of cells in Ca(2+)-free medium led to a 50% inhibition of carbachol induction of p38 kinase activity. Because some of the effects of carbachol are mediated by the small GTP-binding protein Rho, we examined the role of Rho in carbachol induction of p38 kinase activity. We tested the effect of exoenzyme C3 from Clostridium botulinum (C3), a toxin known to ADP-ribosylate and specifically inactivate Rho. C3 led to complete ADP-ribosylation of Rho, and it inhibited carbachol induction of p38 kinase by 50%. We then tested the effect of SB-203580 and C3 on carbachol-stimulated uptake of [(14)C]aminopyrine (AP). Inhibition of p38 kinase by SB-203580 led to a dose-dependent increase in AP uptake induced by carbachol, with maximal (threefold) effect at 10 microM SB-203580. Similarly, preincubation of parietal cells with C3 led to a twofold increase in AP uptake induced by carbachol. Thus carbachol induces a cascade of events in parietal cells that results in activation of p38 kinase through signaling pathways that are at least in part dependent on Rho activation and on the presence of extracellular Ca(2+). p38 kinase appears to inhibit gastric acid secretion.

Ca2+/calmodulin-dependent protein kinase II isoenzymes gamma and delta are both present in H+/K+-ATPase-containing rabbit gastric tubulovesicles

Ca2+/calmodulin-dependent protein kinase II is thought to participate in M3 muscarinic receptor-mediated acid secretion in gastric parietal cells. During acid secretion tubulovesicles carrying H+/K+-ATPase fuse with the apical membrane. We localized Ca2+/calmodulin-dependent protein kinase II from highly purified rabbit gastric tubulovesicles using Ca2+/calmodulin-dependent protein kinase II isoform-specific antibodies, in vitro phosphorylation and pharmacological inhibition of Ca2+/calmodulin-dependent protein kinase II activity by the potent Ca2+/calmodulin-dependent protein kinase II inhibitor KN-62. The presence of Ca2+/calmodulin-dependent protein kinase II in tubulovesicles was shown by immunoblot detection of both Ca2+/calmodulin-dependent protein kinase II-gamma (54 kDa) and Ca2+/calmodulin-dependent protein kinase II-delta (56.5 kDa). The immunoprecipitated Ca2+/calmodulin-dependent protein kinase II from tubulovesicles showed Ca2+/calmodulin-dependent protein kinase activity by phosphorylating autocamtide-II, a specific synthetic Ca2+/calmodulin-dependent protein kinase II substrate. KN-62 inhibited the in vitro autophosphorylation of tubulovesicle-associated Ca2+/calmodulin-dependent protein kinase II (IC50 = 11 nM). During the search for potential Ca2+/calmodulin-dependent protein kinase II substrates we identified different proteins associated with tubulovesicles, such as synaptophysin and beta-tubulin immunoreactivity, which were identified using specific antibodies. These targets are known to participate in intracellular membrane traffic. Ca2+/calmodulin-dependent protein kinase II is thought to play an important role in regulating tubulovesicular motor activity and therefore in acid secretion.

Morphological and functional restoration of parietal cells in helicobacter pylori associated enlarged fold gastritis after eradication

BACKGROUND/AIM

Helicobacter pylori infections are associated with hypochlorhydria in patients with pangastritis. It has previously been shown that eradication of H pylori leads to an increase in acid secretion in H pylori associated enlarged fold gastritis, suggesting that H pylori infection affects parietal cell function in the gastric body. The aim of this study was to evaluate the effects of H pylori infection on parietal cell morphology and function in hypochlorhydric patients.

PATIENTS/METHODS

The presence of H pylori infection, mucosal length, and inflammatory infiltration were investigated in six patients with enlarged fold gastritis and 12 patients without enlarged folds. Parietal cell morphology was examined by immunohistochemistry using an antibody against the alpha subunit of H(+),K(+)-ATPase and electron microscopy. In addition, gastric acid secretion and fasting serum gastrin concentration were determined before and after the eradication of H pylori.

RESULTS

In the H pylori positive patients with enlarged fold gastritis, fold width, foveolar length, and inflammatory infiltration were increased. In addition, the immunostaining pattern of H(+), K(+)-ATPase was less uniform, and the percentage of altered parietal cells showing dilated canaliculi with vacuole-like structures and few short microvilli was greatly increased compared with that in H pylori positive patients without enlarged folds. After eradication, fold width, foveolar length, and inflammatory infiltrates decreased and nearly all parietal cells were restored to normal morphology. On the other hand, altered parietal cells were negligible in H pylori negative patients. In addition, the basal acid output and tetragastrin stimulated maximal acid output increased significantly from 0.5 (0.5) to 4.1 (1.5) mmol/h and from 2.5 (1.2) to 13.8 (0.7) mmol/h (p<0.01), and fasting serum gastrin concentrations decreased significantly from 213.5 (31.6) to 70.2 (7.5) pg/ml (p<0.01) after eradication in patients with enlarged fold gastritis.

CONCLUSION

The morphological changes in parietal cells associated with H pylori infection may be functionally associated with the inhibition of acid secretion seen in patients with enlarged fold gastritis.

Hypothesis--origin of parietal cells: transfer of the H+K+-ATPase gene from parasitic microorganisms to Cnidaria?

Parietal cells present in the stomach and terminal ileum secrete a highly-concentrated hydrochloric acid into the lumen. The cells are characterized by the enzyme P-type H+K+-ATPase, which has an alpha-subunit with a high homology (>85%) for the amino acid sequences of frog, mouse and pig stomachs. Gastric H+K+-ATPase also exhibits a high homology to H+-ATPase in yeast and Na+K+-ATPase in many tissues, suggesting origination from a common ancestral ATPase. It is known that parietal cells first appeared in fish and were later expressed in evolutionarily-higher organisms. Primitive organisms, such as Cnidaria and Ctenophora, that possessed digestive organs, but not parietal cells, were abundant in the ocean more than 600 million years ago (Pre-Cambrian period). The author thus hypothesized that the genes of either H+-ATPase or H+K+-ATPase that were present in parasitic microorganisms, such as yeast, were transferred to the interstitial cells of host organisms, such as Cnidaria, eventually leading to the evolution of parietal cells. It appears that although parietal cells in the stomach developed by chance, such cells have greatly contributed to the evolution of advanced organisms, including humans, by affording safe ingestion of a large volume of various foods.

Expression of rab11a N124I in gastric parietal cells inhibits stimulatory recruitment of the H+-K+-ATPase

Stimulation of the gastric parietal cell results in a massive redistribution of H+-K+-ATPase from cytoplasmic tubulovesicles to the apical plasma membrane. Previous studies have implicated the small GTPase rab11 in this process. Using matrix-assisted laser desorption mass spectrometry, we confirmed that rab11 is associated with H+-K+-ATPase-enriched gastric microsomes. A stoichiometry of one rab11 per six copies of H+-K+-ATPase was estimated. Furthermore, rab11 exists in at least three forms on rabbit gastric microsomes: the two most prominent resemble rab11a, whereas the third resembles rab11b. Using an adenoviral expression system, we expressed the dominant negative mutant rab11a N124I in primary cultures of rabbit parietal cells under the control of the tetracycline transactivator protein (tTA). The mutant was well expressed with a distribution similar to that of the H+-K+-ATPase. Stimulation of these cultures with histamine and IBMX was assessed by measuring the aminopyrine (AP) uptake relative to resting cells (AP index). In experiments on six culture preparations, stimulated uninfected cells gave an AP index of 10.0 +/- 2.9, whereas parallel cultures expressing rab11a N124I were poorly responsive to stimulation, with a mean AP index of 3.2 +/- 0. 9. Control cultures expressing tTA alone or tTA plus actin responded equally well to stimulation, giving AP index values of 9.0 +/- 3.1 and 9.6 +/- 0.9, respectively. Thus inhibition by rab11a N124I is not simply due to adenoviral infection. The AP uptake data were confirmed by immunocytochemistry. In uninfected cells, H+-K+-ATPase demonstrated a broad cytoplasmic distribution, but it was cleared from the cytoplasm and associated with apically derived membranes on stimulation. In cells expressing rab11a N124I, H+-K+-ATPase maintained its resting localization on stimulation. Furthermore, this effect could be alleviated by culturing infected cells in the presence of tetracycline, which prevents expression of the mutant rab11. We therefore conclude that rab11a is the prominent GTPase associated with gastric microsomes and that it plays a role in parietal cell activation.