Gastric parietal cell development: expression of the H+/K+ ATPase subunits coincides with the biogenesis of the secretory membranes

The early development of the parietal cell in the embryonic murine gastric mucosa was investigated with particular attention paid to the biogenesis of the secretory membranes and the localization of the gastric H+/K+ ATPase alpha and beta subunits. Gastric glands were recognized in the day 18 foetus. However, at this stage in development no parietal cells could be distinguished ultrastructurally in the glands, and no immunoreactivity was detected with monoclonal antibodies to either the alpha or beta subunits of the gastric H+/K+ ATPase. In the 19 day embryo, parietal cells were recognizable morphologically by the presence of slender microvilli on the apical (lumenal) surface and differentiating intracellular canaliculi in the apical cytoplasm. Both subunits of the proton pump were found to be specifically associated with the apical and canalicular membranes and with the membranes of relatively large vesicles distributed in the subapical cytoplasm and the cytoplasm surrounding the canaliculi. In the parietal cells of the day 1 neonate, the intracellular canaliculi had extended basally to form the extensive compartments typical of parietal cells in the adult animal. Again, profiles of vesicles showing H+/K+ ATPase immunoreactivity were present in the pericanalicular cytoplasm. These results indicate that the intracellular canaliculi are formed by expansion of the apical surface and suggest that the delivery of newly synthesized gastric H+/K+ ATPase alpha and beta subunits to the apical plasma membrane is mediated by typical Golgi transport vesicles. The large immunoreactive vesicles that occur in the apical and pericanalicular cytoplasm of the developing cells may represent artefacts generated by fixation-induced fragmentation of the differentiating canalicular membrane system during preparation.

Characterization of human autoantibodies reactive to gastric parietal cells

Human sera from autoimmune gastritis patients containing autoantibodies to gastric parietal cells were analyzed by immunological methods. Enzyme linked immuno-sorbent assay demonstrated that all nine sera reacted with pig gastric vesicles enriched in H+/K(+)-ATPase (gastric proton pump). Immunoblotting experiments indicated that the alpha subunit of the H+/K(+)-ATPase was the major antigen in the vesicles with two of the sera reacting strongly. We further characterized the specificity of the antibodies using partial sequences of the pig alpha subunit fused with truncated TrpE (anthranilate synthase). The antibodies from autoimmune gastritis patients reacted differently to the two fusion proteins (Met-1 to Ala-79, and Arg-606 to Ile-964), indicating that each patient sera contains a mixture of autoantibodies recognizing different epitopes with variable contents.

Gastric parietal cell H(+)-K(+)-ATPase microsomes are associated with isoforms of ankyrin and spectrin

Stimulation of HCl secretion by gastric parietal cells requires the fusion of cytoplasmic H(+)-K(+)-ATPase-bearing tubulovesicles with the apical membrane. This insertion of membrane results in a dramatic increase in apical surface area through the formation of microvilli. To elucidate the elements that may stabilize the newly inserted H(+)-K(+)-ATPase within the apical membrane, we searched for specific cytoskeletal proteins associating with the gastric enzyme. We document by immunoblot analysis that ankyrin, spectrin, and actin copurify with H(+)-K(+)-ATPase microsomes prepared from gastric parietal cells. Coprecipitation of 125I-labeled native erythrocyte ankyrin with the H(+)-K(+)-ATPase from gastric microsomes using anti-H(+)-K(+)-ATPase antibodies suggests that ankyrin associates with the H(+)-K(+)-ATPase. Indirect immunofluorescence and confocal microscopy show that ankyrin and H(+)-K(+)-ATPase cosegregate within resting and secreting parietal cells. Taken together, these data suggest that the association of the gastric H(+)-K(+)-ATPase with spectrin and actin is mediated by ankyrin and that this interaction contributes to the maintenance of the polarized distribution of the enzyme to the apical domain of gastric parietal cells during acid secretion.

Alpha and beta subunits of the gastric H+/K(+)-ATPase are concordantly targeted by parietal cell autoantibodies associated with autoimmune gastritis

We have previously shown that parietal cell autoantibodies predominantly react with a 60-90 kDa gastric autoantigen, subsequently identified as the beta subunit of the gastric H+/K(+)-ATPase (EC 3.6.1.3) (proton pump) whereas Karlsson et al showed that these autoantibodies primarily target the 95 kDa alpha subunit of the pump. In view of these discordant results, we have reassessed the reactivity of parietal cell autoantibodies with the two subunits of the gastric H+/K(+)-ATPase. We show here that all 26 parietal cell autoantibody-positive sera immunoblot both subunits under appropriate, but mutually exclusive, conditions. Thus, reactivity of anti-parietal cell autoantibodies with the 95 kDa alpha subunit is optimal when the SDS-PAGE is carried out with samples which are reduced but not boiled. Whereas reactivity with the 60-90 kDa beta subunit is optimal with samples which are boiled but not reduced. Autoantibody reactivity with the beta subunit is critically dependent on the presence of a full complement of N-linked glycans since partially deglycosylated protein, and recombinant beta subunit expressed in COS cells, bearing high mannose N-glycans, failed to bind to the autoantibody. These studies also suggest that B cell auto-epitopes are located on the lumenal domain of the beta subunit. Reactivity of parietal cell autoantibodies with a bacterial fusion protein incorporating the catalytic cytoplasmic domain of the alpha subunit suggests the presence of auto-epitopes in this region of the molecule.

Enterochromaffin-like cells in rat stomach respond to short-term infusion of high doses of cholecystokinin but not to long-term, sustained, moderate hyperCCKemia caused by continuous cholecystokinin infusion or pancreaticobiliary diversion

The histamine-producing enterochromaffin-like (ECL) cells in the oxyntic mucosa are controlled by gastrin. An acute gastrin challenge induces release and accelerated resynthesis of ECL cell histamine. Long-term stimulation with gastrin causes ECL cell hyperplasia. We set out to study whether the ECL cells respond not only to gastrin but also to cholecystokinin (CCK). A wide dose range of gastrin-14 sulfated and -17 non-sulfated and CCK-8 sulfated (CCK-8s) and non-sulfated (CCK-8) was infused intravenously to rats for 3 h. The activity of the histamine-forming enzyme was measured at termination of infusion. Gastrins and CCK-8s were equally effective in activating the enzyme, whereas sulfated CCK-8 was notably less potent than the other three peptides. Clearly, the receptor responsible for activation of the ECL cells distinguishes poorly between gastrin-17 and CCK-8s, which is in line with the characteristics of the CCK-B receptor. Moreover, neither the response to gastrin-17 nor that to CCK-8s was affected by concomitant infusion of devazepide (200 micrograms/kg/h), a selective CCK-A-receptor antagonist. One group of rats received CCK-8s continuously via a minipump. Another group of rats was subjected to pancreaticobiliary diversion (PBD), which increases the plasma CCK concentration 10- to 20-fold. The rats were killed 7 or 10 weeks later, respectively, and the stomachs were analyzed with regard to mucosal growth and ECL cell hyperplasia. HyperCCKemic rats had increased pancreatic weights but showed no signs of growth stimulation in the stomach and no ECL cell hyperplasia.(ABSTRACT TRUNCATED AT 250 WORDS)

Ca2+-ATPase in mucous and oxyntico-peptic cells of the fowl proventriculus

Calcium adenosine triphosphatase (Ca(2+)-ATPase) was localized by means of histo-and ultracytochemistry in the secretory cells of the proventriculus of the domestic fowl. The mucous cells exhibited plasmalemmal-associated enzyme activity on the external aspect of the basolateral cell membrane. Intracellularly, the luminal aspect of Golgi-membranes and of secretory vesicle membranes reacted positively for Ca(2+)-ATPase activity, as did the apical cytosol and the matrix of lysosomes. Oxyntico-peptic cells were characterized by apical and apico-lateral plasmalemmal activity and by an organelle-associated distributional pattern similar to that in the mucous cells. In addition, Ca(2+)-ATPase was associated either with the matrix of mitochondria or with tubuli of the rough-surfaced endoplasmic reticulum. The results are discussed with respect to messenger and effector functions of calcium in the process of proventricular mucus secretion. In addition, Ca(2+)-ATPase distributional patterns in the oxyntico-peptic cell are related to the unique structure and function of these cells.

Protein kinase C inhibits stimulation of adenylate cyclase by the histamine H2 receptor in rat parietal cells

The action of protein kinase C on the stimulation of adenylate cyclase activity by the histamine H2 receptor was investigated in rat parietal cells. Protein kinase C was activated by preincubating cells with 12-O-tetradecanoylphorbol 13-acetate (TPA), and adenylate cyclase activity was measured in sonicated extracts. TPA (100 nM) inhibited adenylate cyclase activity stimulated by histamine (100 nM-500 microM). This effect was related to the concentration of TPA. TPA (100 nM) enhanced the stimulation of adenylate cyclase activity by forskolin (100 microM) but had no effect on the stimulation by NaF (10 mM). In conclusion, protein kinase C inhibits stimulation of adenylate cyclase by the histamine H2 receptor. This action could be mediated by changes in the number of affinity of histamine H2 receptors or in the coupling of the receptor to the stimulatory guanine nucleotide regulatory subunit Gs.

Interaction of the non-steroidal anti-inflammatory drug flufenamic acid with gastric acid secretion and H+/K(+)-ATPase

1. The effects of the non-steroidal anti-inflammatory drug (NSAID) flufenamic acid on H+ production in isolated and enriched guinea-pig parietal cells and on H+/K(+)-ATPase activity in ion-tight inside-out membrane vesicles from pig gastric mucosa were studied. 2. At low concentrations (0.1 and 1.0 mumol/L), flufenamic acid increased the secretory response of parietal cells to dibutyryl cyclic AMP (dbcAMP). At higher concentrations (10 and 100 mumol/L) it progressively inhibited basal and dbcAMP-stimulated acid production. 3. Flufenamic acid (10 mumol/L) increased K+ (0.5-10.0 mmol/L) and K+ (0.5-1.0 mmol/L) plus gramicidin-stimulated ATPase activity in gastric membrane vesicles. The Km value for K+ (1.6 and 1.0 mmol/L in the absence and presence of gramicidin, respectively) was decreased to 0.8 and 0.5 mmol/L, respectively. At higher concentrations (greater than or equal to 50 mumol/L), flufenamic acid inhibited K+ plus gramicidin-stimulated ATPase activity (inhibited concentration at 50% [IC50] = 186 mumol/L) and reduced the proton concentration (IC50 = 50 mumol/L). 4. It is concluded that flufenamic acid-induced enhancement of dibutyryl cyclic AMP-stimulated H+ production in the parietal cell reflects the stimulation of H+/K(+)-ATPase. We suggest that activation of the enzyme involves increased affinity of K+ towards the K(+)-binding site of the enzyme and/or increased KCl permeability at the vesicle membrane. The inhibitory action of the drug on H+ production in parietal cells results from a detergent and/or protonophoric-like action at the apical parietal cell membrane, and from inhibition of H+/K(+)-ATPase activity.

Distribution of manganese superoxide dismutase in rat stomach: application of Triton X-100 and suppression of endogenous streptavidin binding activity

The distribution of rat manganese superoxide dismutase (Mn-SOD) was immunohistochemically investigated in the rat stomach with a specific polyclonal antibody and a labeled streptavidin-biotin immunoglobulin detection system in cryosections. Parietal cells in the stomach were intensely stained, whereas the other epithelial cells in the gastric gland and pit exhibited only slight staining. Rapid-freezing and freeze-substitution immunoelectron microscopy revealed that Mn-SOD in parietal cells was mainly localized in mitochondria. Therefore, the large amount of Mn-SOD in parietal cells is due to the abundant mitochondria, in which Mn-SOD is considered to play important roles in protecting the ion pump and the cell itself from superoxide insult. Application of Triton X-100, cryosectioning, and the streptavidin-biotin system are needed to distinctly visualize Mn-SOD with our antibody. Treatment of the cryosections with Triton X-100 enhanced not only the immunoreactivity but also the false-positive staining, which showed a similar distribution pattern to that of Mn-SOD and thus made it difficult to determine the localization. The most plausible cause of the false-positive staining is thought to be endogenous biotin in the stomach, which survives paraformaldehyde fixation and is revealed by Triton X-100 treatment. Suppression of the endogenous streptavidin binding activity is important when cryosections, the streptavidin-biotin system, and Triton X-100 are employed.

Localization of gastric peroxidase and its inhibition by mercaptomethylimidazole, an inducer of gastric acid secretion

Mercaptomethylimidazole (MMI) is a potent inducer of gastric acid secretion which is associated with significant inhibition of peroxidase activity of rat gastric mucosa in vivo. A time-dependent increase in acid secretion correlates well with time-dependent decrease in the peroxidase activity. In a chamber experiment in vitro using isolated gastric mucosa, MMI stimulates acid secretion, showing an almost linear response up to 600 microM. The time-dependent increase in acid secretion is also correlated with time-dependent inhibition of the peroxidase activity. This effect is not mediated through oxidation of MMI by flavin-containing mono-oxygenase, which is absent from gastric mucosa. The peroxidase has been localized mainly in parietal cells isolated and purified from gastric mucosa by controlled digestion with collagenase followed by Percoll-density-gradient centrifugation. Peroxidase activity was further localized in the outer membrane of the purified mitochondria of the parietal cell by some membrane-impermeant reagents, indicating outward orientation of the enzyme. MMI can inhibit the peroxidase activity of both the parietal cell and its mitochondria in a concentration-dependent manner. The possible involvement of the parietal-cell peroxidase-H2O2 system in MMI-induced acid secretion may be suggested.

Differential distribution of nitric oxide synthase between cell fractions isolated from the rat gastric mucosa

Cells isolated from the rat gastric mucosa were resolved into two fractions on a percoll density gradient, and into five fractions using counterflow centrifugation (elutriation). Ca(2+)-dependent nitric oxide synthase (NOS) activity was found in the high density percoll fraction but not in the parietal cell enriched low density fraction. This activity was inhibited by NG-monomethyl-L-arginine with an IC50 of 3.7 microM. Cells in the elutriator fraction rich in mucous-epithelial cells exhibited the highest NOS activity, while the smaller cell fractions had no detectable NOS yet had the highest basal release of prostaglandin E2. The parietal cell enriched elutriator fraction again had low NOS activity. The activity of a constitutive NOS in the mucous-cell fraction may indicate a role of NO in the regulation of epithelial cell integrity or secretion.

Immunopurification of gastric parietal cell tubulovesicles

1. The tubulovesicles of hog and rabbit gastric parietal cells were immunopurified from microsomes using monoclonal antibodies against the (H+, K+)-ATPase. 2. The best yields of immunoprecipitation were obtained with an ATPase/mAb molar ratio of 0.3: the immunoprecipitate contained 79 and 90% of the hog and rabbit microsomal PNPPase activity respectively and K(+)-stimulated ATPase specific activity was 221 +/- 29 mumoles Pi per hr and per mg of membrane protein. 3. The immunoprecipitate contained vesicles that were 85% cytoplasmic-side out, like tubulovesicles in vivo, demonstrating that the epitopes were cytoplasmic. 4. The alpha-beta protomer of (H+, K+)-ATPase accounted for 80 +/- 12% of the immunopurified proteins. 5. The major other proteins ran at 80, 75, 69, 57, 47, 44, 39, 34 and 32 kDa on the SDS-PAGE. 6. Comparative analysis between sucrose-gradient purified fractions and immunopurified tubulovesicles demonstrated that carbonic anhydrase and actin were contaminants and that the 53 kDa and presumably the 50 kDa bands of the gradient fraction were alpha and beta subunits of F1 ATPase.

Ultrastructural and cytochemical analysis of Na+, K+, ATPase and H+, K+, ATPase in parietal cells of gastric mucosa in the rabbit

Rabbit gastric secretion has the physiological peculiarity of being continuous and uninfluenced by food intake. In this respect, ultrastructural analysis of rabbit parietal cells has revealed morphofunctional features situated between states of rest and very active acid secretion. Our cytochemical study shows that Mg2+ ATPase and ADPase activities vary from cell to cell and can even be totally absent. These activities concern either microcanaliculi or laterobasal folds or both, but never tubulovesicles. Application of the technique of Mayahara to K+ pNPP, associated or not with inhibitors (ouabain, vanadate, N-ethyl-maleimide, sodium fluoride), enabled us to confirm the coexistence of H+, K+, ATPase and Na+, K+, ATPase activities in the rabbit and to determine that these activities concern basolateral folds, microcanaliculi, hyaloplasm and tubulovesicles. The global activity of K+, pNPPase varied considerably in intensity. The results of using inhibitors suggest that proton transport ceases completely in certain cells. The signs of functional alternation found in this study are in agreement with physiological data relative to this animal.

Production of monoclonal antibodies against gastric parietal cell antigens

Two mice DBA/1 were each immunized with a single injection of one million enriched parietal cells in the hind foot pads. Monoclonal antibodies to be used as research tools in studies on regulatory mechanisms in gastric parietal cells were obtained after fusion of mouse myeloma cells (SP2) with cells from the popliteal lymph nodes of the mice. Twelve hybridomas produced antibodies reactive with structures only present in parietal cells as assessed by immunohistochemistry of oxyntic mucosa sections. Three hybridomas were subcloned and the antibodies produced by them, designated as PC4, PC8, and PC117, were characterized. In an enzyme-linked immunosorbent assay, all antibodies reacted with H,K-ATPase-containing vesicles. The antibody PC8 recognized a 94 kDa protein after immunoblotting of H,K-ATPase-containing vesicles and all antibodies precipitated a 94 kDa protein from [125I]H,K-ATPase-containing vesicles. The antibodies PC4 and PC117 recognized extracellular structures with a polarized distribution in viable, purified parietal cells. The results suggest that the structure recognized by all three antibodies is the alpha-subunit of the H,K-ATPase. The antibodies produced by another hybridoma, PC43, recognized a structure present in parietal and surface epithelial cells of the oxyntic mucosa. In an enzyme-linked immunosorbent assay, they reacted with a high-activity carbonic anhydrase which had been affinity-purified from pig oxyntic mucosa and they recognized a 30 kDa protein after immunoblotting. Thus, monoclonal antibodies against both intracellular and extracellular parietal cell structures were obtained after immunization with a small number of parietal cells.

Diagnostic ELISA for parietal cell autoantibody using tomato lectin-purified gastric H+/K(+)-ATPase (proton pump)

Circulating parietal cell autoantibodies, a useful diagnostic marker for autoimmune gastritis and pernicious anaemia, are currently routinely tested by serum immunofluorescence reactivity with frozen sections of rodent stomach. The major molecular targets of these parietal cell autoantibodies have recently been demonstrated to be the alpha- and the beta-subunits of the gastric H+/K(+)-ATPase (proton pump). We have demonstrated that tomato lectin binds specifically to the beta-subunit of the proton pump and concomittantly co-purifies the alpha-subunit. In the present study, we have exploited the latter observation for the development of a diagnostic ELISA for the detection of parietal cell autoantibodies and compared the performance of this assay with an ELISA using crude gastric membranes. The ELISAs were tested on 72 parietal cell autoantibody-positive sera, 72 parietal cell autoantibody-negative sera and 72 disease-control sera. The ELISA using lectin-purified canine proton pump was superior to that using crude canine gastric membranes in that it was about two-fold more sensitive (82% vs. 43%). With an assay sensitivity of 82% and a specificity of 90%, we propose that the ELISA using the lectin-purified proton pump is a rapid, simple, sensitive and specific diagnostic immunoassay for parietal cell autoantibodies.

An inhibitor of Ca2+/calmodulin-dependent protein kinase II, KN-62, inhibits cholinergic-stimulated parietal cell secretion

Cholinergic stimulation of parietal cell secretion is mediated by an increase in intracellular calcium. KN-62, a selective inhibitor of Ca2+/calmodulin-dependent protein kinase II (CaMK II), has recently been synthesized (Tokomitsu et al. J. Biol. Chem. 265: 4315-4320, 1990). To define the role of CaMK II in parietal cell secretion, we determined the effects of KN-62 on secretagogue-stimulated acid secretion in isolated rabbit parietal cells. Pretreatment of parietal cells with KN-62 resulted in the inhibition of carbachol-stimulated [14C]aminopyrine uptake over a concentration range of 3 to 60 microM (IC50 of 20 microM). KN-62 (60 microM) reduced carbachol-stimulated aminopyrine uptake to unstimulated levels. KN-62 did not alter carbachol-stimulated increases in cytoplasmic free Ca2+ concentration. High concentrations of KN-62 (60 microM) elicited a small decrease in aminopyrine uptake stimulated by forskolin, but did not significantly inhibit histamine stimulation. A potent CaMK II activity was identified in total membrane from parietal cells. These results suggest that CaMK II may mediate cholinergic-stimulated parietal cell secretion.

[Characteristic features of proton pump inhibitors in the inhibition of gastric acid secretion: long-acting and complete inhibition]

Proton pump inhibitor is a compound recently applied for the treatment of peptic ulcers for its strong action to inhibit the gastric acid secretion. It works through inhibition of H+, K(+)-ATPase, so called proton pump, on the luminal surface of secretory canaliculi in the parietal cells, showing remarkable characteristics in the inhibition of gastric acid secretion; e.g., the long-acting and complete inhibition. At neutral pH, the unionized form of this compound as a weak base is lipophilic, and passes through the cell membrane to accumulate as the ionized form in an acidic environment in the secretory canaliculi of parietal cells, where it is transformed to an active molecule which binds covalently to the active site of H+, K(+)-ATPase, forming a highly stable complex. The long-acting and complete inhibition of gastric acid secretion by this compound is derived from this physico-chemical nature. The above characteristics of the proton pump inhibitor have been confirmed with the basal, stimulated and nocturnal gastric acid secretion and the 24-hour intragastric pH of healthy volunteers by several investigators prior to its nation-wide clinical trial in Japan. On the other hand, the increased endocrine and exocrine secretion, such as pepsin secretion and gastrin release, and the increased turnover of gastrointestinal endocrine cells by this compound have been reported in animal models, probably due to its accumulation in the acidic environment.(ABSTRACT TRUNCATED AT 250 WORDS)

The rat H+/K(+)-ATPase beta subunit gene and recognition of its control region by gastric DNA binding protein

The rat gastric H+/K(+)-ATPase beta subunit gene was cloned, and its nucleotide sequence was determined. The coding region is separated by 6 introns, whereas the related human Na+/K(+)-ATPase beta subunit gene was shown to have 5 introns (Lane, L.K., Shull, M.M., Whitmer, K.R., and Lingrel, J.B. (1989) Genomics 5, 445-453). The positions of introns 1, 2, and 5 of the two genes were the same. The similarities in intron/exon organizations and primary structures (30-40% identical residues) suggest that the beta subunit genes for H+/K(+)-ATPases were derived from a common ancestor. The upstream region of the rat H+/K(+)-ATPase beta subunit gene contains direct repeat sequences and palindromes, potential binding sites for RNA polymerase II and E4TF1, and CACCC box sequences. Gel retardation assay demonstrated that the stomach, but not other tissues (liver, brain, kidney, spleen, and lung), has a nuclear protein(s) capable of binding to the regions upstream of the potential RNA polymerase II binding sites (TATA box). The nuclear protein(s) are suggested to recognize three tandem GATAGC sequences and may be important for controlled transcription of the H+/K(+)-ATPase beta subunit gene in gastric parietal cells.

Gastric H,K-ATPase topography: amino acids 888-907 are cytoplasmic

Gastric acidification is mediated by H,K-ATPase, an integral protein of apical membranes of gastric parietal cells. Hydropathy analysis of H,K-ATPase alpha subunit primary structure predicts eight transmembrane (TM) domains, while omeprazole-binding data were interpreted in terms of ten TM domains (Mercier et al. (1991) FASEB J. 5, A749). In the present study, tryptic hydrolysis of gastric mucosal microsomes gave a set of peptides which bound the monoclonal antibody HK 12.18, a highly specific probe of the H,K-ATPase. An antiserum against the C-terminus of H,K-ATPase alpha subunit bound the same peptides, and one smaller peptide. The binding data suggested a putative epitope for HK 12.18, and a 20-mer peptide encompassing this site was synthesized. This peptide bound directly to HK 12.18, displaced HK 12.18 from microsomal H,K-ATPase, and blocked HK 12.18 immunostaining of gastric parietal cells. In addition, intact gastric microsomes competitively inhibited binding of HK 12.18 to peptide-BSA conjugate. Taken together, these data place the HK 12.18 epitope between amino acids 888-907 and identify this domain as cytosolic. This result specifically excludes a pair of TM domains between the sixth and seventh TM alpha helices of the H,K-ATPase and supports a secondary structure model with eight TM domains.

[A morphofunctional analysis of the parietal exocrinocytes of the gastric glands proper after removal of the testes]

In the experiment performed in 52 white male rats by means of light electron microscopy methods, cytochemistry and biochemistry with a subsequent cytophoto- and morphometric analysis, it has been stated that bilateral removal of the testes does not inhibit essentially the differential process of the parietal exocrinocytes, but facilitates the development of certain dystrophic processes in them. The latter are demonstrated as decrease of secretory membranes balance in the cell, of quantitative density of mitochondria, of crysts area, of matrix vacuolization. Activity of oxidoreductase in Krebs cycle, of pentosophosphate shunt and glycolysis decreases. Most of the changes mentioned are not large, but stable. Despite this, acid-producing function of the parietal exocrinocytes is essentially inhibited.

Gastric lipase and pepsinogen during the ontogenesis of rabbit gastric glands

In rabbit stomach, gastric lipase activity level was found to increase from birth to 30 days old (weaning), and then decreased. In contrast, pepsin activity only appeared between 30 to 45 days old, and increased till to the adult level. It was observed that maturation of gastric glands in cardial mucosa was a downward elongation process from the mitotic cell pool. These mitotic cells were always found in the neck of the gastric glands, corresponding to the bottom of the gland at 6 days old and to the mid-zone of the gland in adult. Location of rabbit gastric lipase (RGL) cells in cardial glands varied with age and was found along the pit of the gastric glands at 6 days old. The extent of this cellular location decreased with age, whereas a second RGL cell zone appeared below the mitotic cell area at 18 and 30 days old. At 45 days old, the pepsinogen cells appeared in the bottom of the gland, and consequently the RGL cells were located in the mid-zone of the gastric glands, between mitotic cells (neck of the gland) and pepsinogen cells (lower part of the gland). Ultrastructural study of cardial gastric glands revealed different morphologies of the secretion granules in the cells along the gastric glands. In 6-day-old rabbits, secretory granules were found uniformly electron dense in the bottom of the glands and were RGL-labeled by the immunogold technique. In the medium part of the glands, granules appeared biphasic, with a clear and a dense part, and RGL labeling was confined to the electron-dense part.(ABSTRACT TRUNCATED AT 250 WORDS)

Peptic ulcer disease: absence of antibodies stimulating the histamine sensitive adenylate cyclase of gastric mucosal cells

The possible presence of parietal cell stimulating antibodies was examined in sera from 57 patients with relapsing ulcer disease. The sera were obtained at the time of symptomatic relapse and all patients had ulcers confirmed by endoscopy. A sensitive assay based on adenosine 3':5' cyclic monophosphate (cAMP) production in isolated porcine gastric mucosal cells was used as a measure. cAMP production increased up to four hours of incubation and was histamine responsive; an approximately 20-fold increase was found with histamine 10(-4) mol/l. Sera from both patients and healthy control subjects showed some inhibitory effect on basal cAMP production compared with incubation in medium only, whereas immunoglobulin preparations had a weaker non-specific effect. No stimulation was found when the patients' sera and immunoglobulins (up to a concentration of 6 mg/ml) were examined. These results suggest that gastric acid hypersecretion in duodenal ulcer disease is not an effect of histamine receptor stimulating antibodies. The data thus argue against a recent hypothesis that severe chronic ulcer disease in some patients has an autoimmune origin.

Effect of omeprazole on gene expression in canine gastric parietal cells

Stimulation of gastric parietal cells by carbachol induces coordinate expression of the genes for two enzymes involved in the process of acid secretion, H(+)-K(+)-ATPase and carbonic anhydrase II (CA II). The basis of this coordinate expression was examined in experiments using parietal cells that had been pretreated with omeprazole. We observed a twofold increase in the steady-state mRNA levels of both H(+)-K(+)-ATPase and CA II after cells were treated with the inhibitor. The induction of CA II mRNA by carbachol followed the same kinetics in omeprazole-pretreated cells as in those that were not pretreated, suggesting that the induction of CA II gene expression by carbachol was not dependent on activation of the gastric H(+)-K(+)-ATPase. In addition, carbachol stimulation of omeprazole-pretreated cells resulted in an induction of one or more larger mRNA species that hybridized with the H(+)-K(+)-ATPase probe. The observation that carbachol-induced increases in steady-state levels of beta-actin mRNA in parietal cells could be inhibited by omeprazole pretreatment suggests a possible linkage between increased beta-actin gene expression and the process of acid secretion.

Carbonic anhydrase II in rat acid secreting cells: comparison of osteoclasts with gastric parietal cells and kidney intercalated cells

Location of carbonic anhydrase II, an important enzyme involved in acid production, was studied using an immunogold method on ultracryosections. Its distribution in osteoclasts was compared with that in gastric parietal cells and kidney intercalated cells of the inner stripe of outer medulla. It is shown that the distribution of carbonic anhydrase II is much similar in all of these acid producing cells: most of the enzyme is cytoplasmic and nucleoplasmic and only a small fraction of the enzyme is associated with the apical plasma membrane. It seems likely that carbonic anhydrase II has a similar role in all of these acid producing cells.

Ontogeny of gastric H(+)-K(+)-ATPase in suckling rabbits

Gastric mucosal homogenates were prepared from resting and stimulated stomachs of rabbits, age 3-57 days postnatal, and fractionated by differential centrifugation. Total H(+)-K(+)-adenosinetriphosphatase (ATPase) (assayed as K(+)-dependent ouabain-insensitive hydrolysis of p-nitrophenyl phosphate) was low in the first 3 wk but rapidly accumulated between days 20 and 43. Specific activity rose eightfold from day 3 to a typically adult level of 2 mumol.mg-1.h-1 by day 43. The microsomal fraction (P3) was subfractionated on sucrose gradients (20, 27, and 33% steps or 10-40% continuous gradient). H(+)-K(+)-ATPase from P3 of resting stomachs was distributed bimodally on the continuous gradients, with activity mainly in the denser peak (or on the 33% sucrose step) before day 20, but accumulating mainly in the lighter peak (or in the lighter step-gradient fractions) after day 20. Throughout the age range tested, in vivo stimulation with histamine just before removal of the stomach caused a loss of most H(+)-K(+)-ATPase from P3 and an increase in H(+)-K(+)-ATPase in a lower-speed fraction P1. Thus, even in the 1st postnatal wk, when H(+)-K(+)-ATPase is low, most of the enzyme occurs in cells with histamine H2 receptors and all the intracellular mechanisms for fusion of oxyntic cell tubulovesicles (enriched in P3) with the apical membrane (enriched in P1). These studies delineate a 3-wk period of sharply accelerated synthesis of H(+)-K(+)-ATPase before weaning. Age-related changes in distribution of H(+)-K(+)-ATPase among microsomal density subfractions suggest maturational changes either in the intracellular partitioning of the enzyme or in properties of the membranes containing the enzyme.