The ontogeny of rat gastric H+/K+-ATPase

Effect of vagotomy on central nesfatin-1-induced decrease in gastric acid secretion

AIM: To observe the effect of gastric acid secretion decrease induced by intracerebroventricular (ICV) injection of nesfatin-1.

METHODS: Male Sprague-Dawley rats were randomly and equally divided into a control group and a nesfatin-1 group after implantation of an ICV cannula. The nesfatin-1 group was injected intracerebroventricularly with different concentrations of nesfatin-1, and the control group was treated with the same amount of distilled water (5 μL/rat). The volume of gastric secretion was measured and the amount of gastric acid was determined by titration with NaOH. H⁺/K⁺-ATPase mRNA expression was detected by real-time quantitative PCR. Activity of H⁺/K⁺-ATPase was determined indirectly by measuring K⁺-stimulated p-nitrophenyl phosphatase (pNPPase) activity. In another group of animals, rats were divided into a vagotomy and a sham group. The treatments and measurements were the same as above.

RESULTS: Intracerebroventricular infusion of nesfatin-1 significantly reduced gastric acid output, and the maximum inhibitory effect on gastric acid output was detected at a dose of 50 pmol/rat. Furthermore, nesfatin-1 decreased H⁺/K⁺-ATPase mRNA expression and activity in gastric mucosal tissue compared to the control group. The inhibitory action of nesfatin-1 on the acid output and H⁺/K⁺-ATPase expression and activity was abolished by vagotomy.

CONCLUSION: Nesfatin-1 injected intracerebroventricularly induces a dose-dependent decrease in gastric acid secretion in rats and the vagal nerve may be involved in the process of the effect of nesfatin-1.

Effect of Nesfatin-1 on gastric acid secretion in rats

AIM: To investigate the effect of Nesfatin-1 on gastric acid secretion in rats.

METHODS: Thirty-six male Sprague-Dawley rats were randomly and equally divided into six groups to receive intracerebroventricular injection of 0.05, 0.5 μg of Nesfatin-1 or sterile water and intravenous injection of 10, 50 μg/kg of Nesfatin-1 or sterile water. Gastric secretion was measured using the pylorus-ligation method. Three hours after treatment, rats were killed to remove the stomach and collect the gastric contents. The volume of gastric secretion was measured and the amount of gastric acid was determined by titration with NaOH. H⁺-K⁺-ATPase mRNA expression was detected by RT-PCR.

RESULTS: Intracerebroventricular infusion of 0.05 or 0.5 μg of Nesfatin-1 significantly reduced the volume of gastric juice (3.3 mL/3 h ± 0.3 mL/3 h vs 2.4 mL/3 h ± 0.3 mL/3 h; 3.3 mL/3 h ± 0.3 mL/3 h vs 2.5 mL/3 h ± 0.3 mL/3 h, both P < 0.05), inhibited gastric acid output (582.7 μmol/3 h ± 59.3 μmol/3 h vs 373.6 μmol/3 h ± 61.5 μmol/3h, 582.7 μmol/3 h ± 59.3 μmol/3h vs 380.0 μmol/3 h ± 55.8 μmol/3h, both P < 0.05), and decreased gastric H⁺-K⁺-ATPase mRNA expression (both P < 0.05). Intravenous injection of 10 or 50 μg/kg of Nesfatin-1 had no significant effect on the volume of gastric juice (3.7 mL/3 h ± 0.7 mL/3 h vs 3.3 mL/3 h ± 0.4 mL/3 h, 3.7 mL/3 h ± 0.7 mL/3 h vs 3.8 mL/3 h ± 0.5 mL/3 h, both P > 0.05), gastric acid output (647.6 μmol/3 h ± 102.8 μmol/3 h vs 573.8 μmol/3 h ± 97.4 μmol/3 h, 647.6 μmol/3 h ± 102.8 μmol/3 h vs 594.4 μmol/3 h ± 121.0 μmol/3 h, both P > 0.05) and gastric H⁺-K⁺-ATPase mRNA expression (both P >0.05 ).

CONCLUSION: Nesfatin-1 acts in the central nervous system to inhibit gastric acid secretion in rats.

Ghrelin stimulates gastric acid secretion by rat gastric mucosal cells in vitro

AIM: To investigate the effects of ghrelin on gastric exocrine secretion.

METHODS: Gastric mucosa was obtained from weaned rats. Gastric mucosal cells were dispersed from freshly obtained gastric mucosa and divided into two groups: treatment group and control group. The treatment group was incubated with fresh culture medium containing different concentrations of ghrelin (1 × 10^-4, 1×10^-3, 1 × 10^-2 and 1 × 10^-1 μmol/L), while the control group was incubated with fresh culture medium without ghrelin. Four hours after incubation, culture supernatants were collected, and cells were harvested. Cell viability was measured by methyl thiazolyl tetrazolium (MTT) assay. Pepsin activity and H⁺-K⁺-ATPase mRNA expression and activity were evaluated.

RESULTS: No significant difference was noted in cell viability between the control group and treatment group. Ghrelin at a concentration of 1 × 10^-3 μmol/L significantly augmented pepsin activity and H⁺-K⁺-ATPase mRNA expression (both P < 0.05). Ghrelin at a concentration of 1 × 10^-4 and 1 × 10^-3 μmol/L significantly increased H⁺-K⁺-ATPase activity in gastric mucosal cells (both P < 0.05).

CONCLUSION: Ghrelin can significantly stimulate the secretion of both pepsin and gastric acid by gastric mucosal cells in vitro.

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

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

Gastric proton pump is expressed in the inner ear and choroid plexus of the rat

Inner ear fluids and cerebrospinal fluid show remarkably stable ionic concentrations, particularly that of K(+) and H(+), but the mechanisms which control the homeostasis of these media are not well understood. We investigated a possible role of the gastric H, K-ATPase (gH,K-ATPase) pump in this control since this pump is known to be expressed in other tissues than gastric parietal cells. Here, we show by reverse transcription-polymerase chain reaction that the rat gH,K-ATPase alpha- and beta-subunits are expressed in the inner ear (lateral wall, organ of Corti and spiral ganglion cells), while only the alpha-subunit is expressed in the choroid plexus (CP). The presence of the alpha-subunit in the inner ear and CP was confirmed by immunoblotting. Immunohistochemistry localized this protein in the intermediate cells of the stria vascularis, in the spiral ligament and the spiral ganglion. gH,K-ATPase could be involved in the maintenance of H(+) and K(+) equilibria in cerebrospinal and labyrinthine fluids.

Early development of human gastric H,K-adenosine triphosphatase

BACKGROUND

Little is known about the early development of the gastric acid secretion in human neonates. The purpose of this study was to examine the early development of gastric H,K-adenosine triphosphatase (ATPase) by analyzing human gastric biopsy specimens.

METHODS

Eighty-eight neonates from week 25 to week 42 of gestation who were treated in a neonatal intensive care unit underwent gastroscopy with biopsy specimens obtained from the corpus. The expression of gastric H,K-ATPase protein in the gastric biopsy specimens was assessed by Western blot analysis, using an antibody directed against the gastric H,K-ATPase. The amount of H,K-ATPase expressed was compared with age, gender, clinical factors, diseases, and the macroscopic and histologic findings at endoscopy.

RESULTS

The expression of human gastric H,K-ATPase increased significantly with gestational age. There was a significant increase in the expression of gastric H,K-ATPase during the first 82 days after birth. Boys had a significantly higher expression of gastric H,K-ATPase than girls did, when it was adjusted for gestational and postnatal age. Neither the clinical features nor treatments showed significant correlations with the expression of human gastric H,K-ATPase when controlling for gestational and postnatal age.

CONCLUSIONS

This study shows that human gastric H,K-ATPase is expressed from week 25 of gestation, which agrees with earlier findings of gastric pH in preterm infants. The amount of enzyme expressed increases with gestational and postnatal age. The authors speculate that the susceptibility to gastric lesions seen in neonates is not related to the amount of H,K-ATPase. However, studies elucidating the ontogeny of gastric mucosal defense mechanisms are warranted.

Glucocorticoids stimulate the maturation of H,K-ATPase in the infant rat stomach

The development of gastric H,K-ATPase from fetal to adult life was studied in the rat. The alpha and beta H,K-ATPase mRNA abundance, the protein abundance, and the enzyme activity increased postnatally. The sharpest increase in mRNA and enzyme activity was observed in the weaning period. Several intestinal enzymes are known to be stimulated by glucocorticoids at the time of weaning. To study the role of glucocorticoids in the maturation of gastric H,K-ATPase, we treated 10-d-old rats with a single injection of betamethasone. Twenty-four hours after betamethasone injection, the enzyme activity was significantly higher than in the control animals (2.6-fold, p < 0.05). The abundance of catalytic alpha H,K-ATPase protein was also increased (2.5-fold, p < 0.01). The time-dependent effect of betamethasone on alpha H,K-ATPase mRNA was determined from 6 to 24 h after treatment. Glucocorticoids did not significantly alter the mRNA abundance within 18 h. Twenty-four hours after injection, the gastric H,K-ATPase mRNA was significantly increased compared with controls (2.8- and 2.2-fold increase for alpha and beta subunits, respectively, P < 0.01 for both). In conclusion this study indicates that glucocorticoids may regulate the long-term maturation of gastric H,K-ATPase by indirectly stimulating enzyme synthesis.

Effects of ranitidine on gastric vesicles containing H+,K(+)-adenosine triphosphatase in rats

BACKGROUND

To ascertain the mechanism for rebound acid hypersecretion after treatment with an H2-receptor blocker, we investigated the effects of ranitidine on gastric H+,K(+)-adenosine triphosphatase (ATPase) in rats.

METHODS

Male Wistar rats received ranitidine (1-50 mg/kg body weight intraperitoneally twice a day for 5 days). The rats were starved for 15 h after the last treatment and then killed, and gastric vesicles containing H+,K(+)-ATPase were prepared.

RESULTS

Treatment with ranitidine dose-dependently increased protein content in the gastric vesicular fraction purified from the gastric mucosa without changing total protein content. Ranitidine also increased the content of a 94,000-dalton protein, the catalytic subunit of H+,K(+)-ATPase. On the other hand, ranitidine did not affect the specific activity of the enzyme (mumol/min/mg of the gastric vesicular protein). Since gastric vesicles in the fasting state mainly consist of the tubulovesicular membrane, these results suggest that ranidine administration increases total tubulovesicular H+,K(+)-ATPase content (mumol/min/rat) by increasing the number of tubulovesicles per parietal cell. The ranitidine-induced increase in total tubulovesicular H+,K(+)-ATPase activity was still evident 1 week after treatment and returned to control level 1 month later.

CONCLUSIONS

All these findings suggest that the increased content and total activity of tubulovesicular H+,K(+)-ATPase after ranitidine treatment may contribute to the mechanism for acid rebound after H2-blocker therapy.

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.

H+/K(+)-ATPase contents of human, rabbit, hog and rat gastric mucosa

A monoclonal antibody (mAb 95-111) was used to titrate the amounts of H+/K(+)-ATPase in subcellular fractions of the fundus of rats, pigs, rabbits and humans. All four had similar amounts of H+/K(+)-ATPase: 2.1 +/- 0.5 (human), 1.9 +/- 0.4 (rabbit), 4.4 +/- 0.5 (rat) and 4.2 +/- 0.8 (hog) mg ATPase/g wet tissue. The antigen concentrations and H+/K(+)-ATPase enzymatic activities of subcellular fractions were linearly correlated in all species but rat suggesting that human, rabbit and hog H+/K(+)-ATPases have similar rates of catalysis (223 mumol Pi/h per mg ATPase). The non-correlation of rat data probably reflects the known lability of the rat enzyme. Hence, immuno-titration promises to be a more reliable method of estimating rat ATPase than the currently used enzymatic assay. The H+/K(+)-ATPase content of human biopsies was 20-fold higher than previously-published (Smolka, A. and Weinstein, W.M. (1986) Gastroenterology 90, 532-539) suggesting that the previous immuno-titration underestimated the H+/K(+)-ATPase content of the human fundus.

A monoclonal antibody which inhibits H+/K(+)-ATPase activity but not chloride conductance

A mouse monoclonal antibody was raised against hog gastric membranes. This antibody (95-111 mAb) has a very high affinity for the 95 kDalton band of H+/K(+)-ATPase-enriched membranes, and does not react with Na+/K(+)-ATPase. The epitope is located on the tubulovesicles and canaliculi of the parietal cells. The 95-111 mAb also inhibits the ATP hydrolytic activity, decreases the steady-state phosphorylation level and inhibits the phosphatase activity of H+/K(+)-ATPase, strongly suggesting that the epitope is on the catalytic subunit of H+/K(+)-ATPase. The 95-111 mAb also recognizes rat, rabbit and human gastric H+/K(+)-ATPase. This mAb differs from the H+/K(+)-ATPase-inhibiting mAb previously described (Asano et al. (1987) J. Biol. Chem. 262, 13263-13268), in that it does not inhibit the chloride conductance opened by Cu-o-phenanthroline in gastric vesicles.