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B Wallmark

Publications and source records attributed to B Wallmark.

At least 55 records · Page 3Linked to original sources
PubMed1986

Inhibitory action of omeprazole on acid formation in gastric glands and on H+,K+-ATPase isolated from human gastric mucosa.

The inhibitory effect of omeprazole on acid formation has been studied in vitro in gastric glands and partly purified H+,K+-ATPase, prepared from mucosa obtained either from healthy subjects by gastroscopic biopsy or from gastric ulcer patients during antrectomy. The effect of omeprazole was compared with the inhibitory pattern of the H2-antagonist cimetidine. Acid production in the glands was determined by measuring the accumulation of 14C-aminopyrine. In glands isolated from patients, omeprazole inhibited acid production maximally stimulated by histamine, db-cAMP, and potassium in a dose-dependent manner, with an IC50 value of about 50 nM irrespective of the agonist used. In contrast, cimetidine inhibited only histamine-induced aminopyrine accumulation, with an IC50 of about 30 micron. The inhibitory effect of omeprazole in db-cAMP-stimulated glands from healthy volunteers was of the same magnitude as seen in glands from gastric ulcer patients. Basal aminopyrine accumulation in glands from both patients and healthy volunteers was almost totally inhibited by omeprazole, whereas cimetidine was without effect. Omeprazole also concentration-dependently inhibited the H+,K+-ATPase activity in isolated gastric membrane vesicles. The estimated IC50 value was 4 micron.

Adenosine Triphosphatases↗
PubMed1986

Mechanism of action of omeprazole.

The inhibitory effect of omeprazole on gastric acid secretion in vivo and in vitro is presented. In the gastric fistula dog omeprazole was found to be about 10 times more potent than cimetidine. When omeprazole was administered in vivo, the inhibition of acid secretory rates was found to correlate with the degree of inhibition of the gastric H+K+ATPase purified from the omeprazole treated animals. The inhibitory action of omeprazole was found to depend on acid induced transformation of omeprazole into an active inhibitor of the gastric H+K+ATPase, as no inhibition was obtained when omeprazole was incubated under neutral conditions with either the isolated gastric mucosal or the H+K+ATPase preparations. A model is proposed in which the inhibition of acid formation is mediated by an inhibitory compound generated form omeprazole within the acid compartment of the parietal cell.

Adenosine Triphosphatases↗
PubMed1986

Sulfide and sulfoxide derivatives of substituted benzimidazoles inhibit acid formation in isolated gastric glands by different mechanisms.

The sulfoxide and sulfide forms of three pairs of substituted benzimidazoles, including omeprazole, were investigated using isolated gastric glands and microsomal membranes containing H+,K+-adenosine Triphosphatase (ATPase). The sulfoxides inhibited stimulated aminopyrine (AP) uptake giving IC50 values between 0.47 and 1.1 microM, whereas the sulfides were less potent and showed a greater variation in IC50 values, 9.5 to 170 microM. The decrease in stimulated oxygen consumption induced by the sulfoxides was parallel to their inhibition of AP-uptake, with IC50 values of 0.40 to 3.7 microM, whereas the sulfides were virtually without effect, IC50 greater than 100 microM. The permeable buffers imidazole and 2,6-dimethylpyridine mimiced the effect of the sulfides on both AP accumulation and oxygen consumption. When tested on H+, K+-ATPase, an enzyme suggested to be the proton pump of the gastric mucosa, the sulfoxides inhibited the ATPase activity with IC50 values between 0.25 to 2.8 microM, in contrast to the sulfides, which were without inhibitory action. The sulfoxide-induced inhibition of AP-uptake in gastric glands and H+, K+-ATPase activity was prevented by the addition of beta-mercaptoethanol, whereas the mercaptane was without effect on sulfide-induced inhibition of AP-accumulation. When tested on vesicles containing H+, K+-ATPase, both the sulfide and sulfoxide derivatives dissipated the proton gradient generated by the enzyme, but only the sulfoxide-induced inhibition was prevented by the addition of beta-mercaptoethanol.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphatases↗
PubMed1985

The relationship between gastric acid secretion and gastric H+,K+-ATPase activity.

The H+,K+-ATPase has been postulated to be the enzyme responsible for H+ secretion by the parietal cell. Omeprazole has been shown to be an inhibitor of acid secretion in vivo, but also in in vitro test models for acid secretion, including partly purified H+,K+-ATPase, the inhibitory action of omeprazole has been demonstrated (Wallmark, B., Jaresten, B. M., Larsson, H., Ryberg, B., Brändström, A., and Fellenius, E. (1983) Am. J. Physiol. 245, G64-G71). It was thus possible to use this compound to demonstrate a correlation between H+,K+-ATPase activity in rat oxyntic mucosa and in vivo H+ secretion. Two results were found. (a) Increasing oral doses of omeprazole progressively inhibited acid secretion, H+,K+-ATPase activity, and phosphoenzyme formation of a microsomal fraction isolated from the inhibited rat mucosa. Furthermore, a Mg2+-stimulated ATPase activity, associated with the H+,K+-ATPase membrane fraction, was not affected by the omeprazole treatment. (b) Recovery of H+,K+-ATPase activity following complete omeprazole inhibition was correlated with the appearance of acid secretion. The results indicate a strict relationship between the activity of the gastric H+,K+-ATPase in the microsomal fraction and gastric acid secretion.

Adenosine Triphosphatases↗
PubMed1985

The mechanism for inhibition of gastric (H+ + K+)-ATPase by omeprazole.

Omeprazole was found to inhibit the K+-stimulated ATPase activity of the gastric (H+ + K+)-ATPase in parallel with the K+-stimulated p-nitrophenylphosphatase activity and the phosphoenzyme formation. The degree of inhibition of ATPase activity was directly correlated to the amount inhibitor bound to the enzyme preparation down to about 15% of the control enzyme activity. The acid-decomposed form of omeprazole, i.e. the inhibitory form, was found to react with and bind to sulfhydryl groups within the (H+ + K+)-ATPase preparation with close to a 1:1 stoichiometry. beta-Mercaptoethanol, when added beforehand and in a 10-fold excess of omeprazole, completely prevented binding of the inhibitor and its inhibition of the enzyme. In the presence of beta-mercaptoethanol two different reaction products could be detected in addition to omeprazole; the reduced form of omeprazole (H 168/22), and a product formed between beta-mercaptoethanol and a decomposition product, generated from omeprazole. Under those conditions neither inhibition nor binding was obtained, indicating that none of these three compounds was the inhibitor. Rather, the compound generated from omeprazole and reacting rapidly with either beta-mercaptoethanol or the -SH groups of the enzyme was the likely inhibitor compound. In order to reverse already established inhibition higher concentrations of beta-mercaptoethanol were needed than for protection indicating two different reaction pathways for protection and reversal by beta-mercaptoethanol. The reversal reaction was explained by a two-step reaction; in the first step the bound inhibitor was exchanged for a beta-mercaptoethanol molecule resulting in formation of compound H 168/22 and a mixed disulfide between the enzyme and beta-mercaptoethanol. In the second step, attack of another beta-mercaptoethanol molecule results in liberation of active enzyme and generation of the disulfide form of beta-mercaptoethanol. This hypothesis was substantiated by the fact that when 1 mM beta-mercaptoethanol was added to inhibited enzyme the radiolabel was partially displaced, without any change in the concentration of modified -SH groups.

Adenosine Triphosphatases↗
PubMed1985

The mechanism of action of omeprazole--a survey of its inhibitory actions in vitro.

In order to study the mechanism of inhibition of gastric acid secretion by omeprazole, its action was investigated in several different in vitro preparations. In preparations from isolated gastric mucosa, isolated rabbit gastric glands and isolated parietal cells, omeprazole was found to inhibit both basal and stimulated acid secretion. These effects were seen irrespective of whether acid formation was stimulated by histamine or by db-cAMP. The inhibitory pattern of omeprazole was found to be of a non-competitive nature against db-cAMP stimulation. Furthermore, in isolated glands, omeprazole was found to inhibit stimulation induced by high medium K+ and low Na+ concentrations. The basal membrane of the intact gland preparation was made permeable to molecules of large size by the use of digitonin, and acid secretion was subsequently initiated by the addition of exogenous ATP. Even under these conditions, omeprazole was found to be inhibitory, with an IC50-value comparable to that of intact glands. SCN- was found to mimic the action of omeprazole in that it counteracted both basal and stimulated acid secretion in the test models described above. In contrast, cimetidine was found to inhibit only histamine stimulation, consonant with its H2-receptor-blocking properties. In the gastric gland preparation, changes in oxygen consumption is closely related to changes in acid formation. When oxygen consumption and acid formation were measured in parallel under histamine stimulation, another benzimidazole, timoprazole (H 83/69) (structurally related to omeprazole), was found to inhibit both parameters. However, under non-stimulated conditions, timoprazole was found to have only a minor effect on the oxygen consumption. The isolated H+K+ATPase preparation was used in order to investigate the effects of omeprazole at the "proton pump level". This enzyme was found to be inhibited by omeprazole in a pH-dependent manner. Under neutral or slightly alkaline conditions, slight inhibition occurred. When the pH of the incubation media was progressively decreased, the inhibitory activity of omeprazole was augmented. Several reactions of the H+K+ATPase enzyme cycle were investigated, i.e., K+-stimulated ATPase- and pNPPase- activities and formation of phosphoenzyme. All three of these reactions were inhibited. The results presented are in agreement with the hypothesis that omeprazole inhibits gastric acid secretion by blocking the gastric H+K+ATPase.

Aminopyrine↗
PubMed1984

Evidence for acid-induced transformation of omeprazole into an active inhibitor of (H+ + K+)-ATPase within the parietal cell.

The chemical reactions of omeprazole, leading to inhibition of gastric acid secretion, were investigated. In acid buffer solutions, omeprazole was found to be labile, whereas at physiological pH it was stable (t1/2 greater than 17 h at pH 7.4). The stability of omeprazole was also studied in isolated, acid producing, gastric glands under conditions where acid formation was either stimulated or inhibited. The rate of transformation of omeprazole was high (t1/2 approximately 3 min) under stimulation. Inhibition of acid formation in the gland greatly retarded the decomposition of omeprazole (t1/2 approximately 73 min). The time-course for inhibition of acid formation by omeprazole was parallel to that for decomposition. The major product formed from omeprazole was the reduced form, H 168/22. The inhibitory action of omeprazole was shown to depend on acid-induced transformation, since no inhibition was obtained when omeprazole was incubated under neutral conditions, both in the isolated gastric mucosal- and the (H+ + K+)-ATPase preparations. Despite the fact that H 168/22 was the major product formed in the glandular preparation, it was found to be virtually inactive in both the glandular- and (H+ + K+)-ATPase preparations. Therefore, a model is proposed in which the inhibition of acid formation by omeprazole is mediated by a compound formed during the reduction of omeprazole to H 168/22 within the acid compartments of the parietal cell. Furthermore, mercaptanes, such as beta-mercaptoethanol, were found to prevent as well as reverse inhibition by omeprazole in both the glandular- and (H+ + K+)-ATPase preparations. This indicates that -SH groups are most likely involved in the chemical reactions leading to inhibition of acid secretion.

Adenosine Triphosphatases↗
PubMed1984

[Acid secretion inhibition with new mechanisms of action: substituted benzimidazole].

Omeprazole and other substituted benzimidazoles produce a marked inhibition of gastric acid secretion with a long duration of action. Any kind of stimulated acid secretion is inhibited by the substituted benzimidazoles. The inhibitory mechanism of action is very selective. The substituted benzimidazoles inhibit the parietal cell H+, K+-ATPase, an enzyme which is the proton pump in the secretory membrane of the parietal cell. An oral daily dose of 15 mg omeprazole in humans produced about 80% acid inhibition just after dosage and about 40% 24 hours later. Preliminary results in duodenal ulcer patients show that a daily dose of 20-60 mg omeprazole produces fast ulcer healing in almost all patients.

Animals↗
PubMed1984

Effect of omeprazole on gastric secretion in H+,K+-ATPase and in pepsinogen-rich cell fractions from rabbit gastric mucosa.

In order to study the effects of the substituted benzimidazole omeprazole on gastric secretory functions, parietal cells and chief cells from rabbit gastric mucosa were separated and enriched by density gradient centrifugation in Percoll. H+,K+-ATPase activity, as well as a 100,000 dalton protein, was found to copurify with a cell fraction morphologically characterized as mainly parietal cells (purity approximately 65%), while pepsinogen copurified with a cell fraction morphologically characterized as chief cells (purity approximately 90%). A spontaneous pepsinogen release (9.9 micrograms/mg cell dry wt X 2 hr), unaffected by both atropine and omeprazole, was found in the chief cell fraction. The release was approximately doubled by both carbacholine (4 X 10(-5)M) and dibutyryl cAMP (db-cAMP, 10(-3)M). The cholinergic stimulation was selectively blocked by atropine, while omeprazole had no effect on pepsinogen release induced by either of the secretagogues. On the other hand, omeprazole inhibited both db-cAMP- and histamine-stimulated acid secretion quantified as [14C]aminopyrine (AP) accumulation in the parietal cell fraction. Cimetidine counteracted only acid secretion induced by histamine. These findings indicate that omeprazole has a specific effect on acid secretion, and are consonant with the hypothesis that the effect is due to H+,K+-ATPase inhibition.

Adenosine Triphosphatases↗
PubMed1983

Inhibition of gastric (H+ + K+)-ATPase by the substituted benzimidazole, picoprazole.

The substituted benzimidazole, picoprazole, inhibited the gastric (H+ + K+)-ATPase in a concentration-and time-dependent manner. Half-maximal inhibition of the (H+ + K+)-ATPase activity was obtained at about 2 . 10(-6)M under standard conditions. In addition to the inhibition of ATPase activity, parallel inhibition of phosphoenzyme formation and the proton transport activity were achieved. Radiolabelled picoprazole was found to bind to 100 kDa peptide; this peptide was shown by phosphorylation experiments to contain the catalytic centre of the (H+ + K+)-ATPase. Studies on the (Na+ + K+)-ATPase indicated that this enzyme was unaffected by picoprazole. From the data presented and from other pharmacological studies, it is proposed that this compound inhibits acid secretion at the level of the parietal cell by its ability to inhibit the gastric proton pump, the (H+ + K+)-ATPase.

2-Pyridinylmethylsulfinylbenzimidazoles↗
PubMed1983

Differentiation among inhibitory actions of omeprazole, cimetidine, and SCN- on gastric acid secretion.

The action of the substituted benzimidazole omeprazole (H 168/68) was studied in three different in vitro preparations: the isolated guinea pig gastric mucosa, isolated intact and permeable rabbit gastric glands, and hog fundic microsomal membrane vesicles containing H+-K+-ATPase. The effects of omeprazole were compared with those of cimetidine and thiocyanate (SCN-). Under all the conditions studied, cimetidine only counteracted histamine-induced acid secretion, consonant with its H2-receptor antagonism. In contrast, omeprazole and SCN- were found not only to inhibit histamine-induced secretion but also basal acid formation and acid formation induced by dibutyryl cAMP and a high cell medium concentration of K+. Moreover, acid production induced by ATP in permeable gastric glands was antagonized by omeprazole and SCN-, whereas cimetidine was without effect. The interaction pattern of omeprazole and SCN- was differentiated by studies using the weak base antipyrine in the isolated mucosal preparation, where it was found that antipyrine could reverse the inhibition induced by SCN- but not that of omeprazole. Furthermore, omeprazole was found to inhibit the isolated H+-K+-ATPase, whereas cimetidine or SCN- was without effect. In the isolated mucosal preparation omeprazole caused an increase in K+ secretion rates in parallel with the inhibition of acid formation. This was in contrast to what was observed for cimetidine and SCN-, which exhibited no such increased K+ secretion. The results obtained from intact mucosa and isolated glands are in agreement with the ability of omeprazole to inhibit the isolated H+-K+-ATPase and thus provide evidence of a novel mechanism of action for this inhibitor.

Adenosine Triphosphatases↗
PubMed1982

ATP/ADP exchange activity of gastric (H+ +K+)-ATPase.

The ATP/ADP exchange is shown to be a partial reaction of the (H+ +K+)-ATPase by the absence of measurable nucleoside diphosphokinase activity and the insensitivity of the reaction to P1, P5-di(adenosine-5') pentaphosphate, a myokinase inhibitor. The exchange demonstrates an absolute requirement for Mg2+ and is optimal at an ADP/ATP ratio of 2. The high ATP concentration (K0.5=116 microM) required for maximal exchange is interpreted as evidence for the involvement of a low affinity form of nucleotide site. The ATP/ADP exchange is regarded as evidence for an ADP-sensitive form of the phosphoenzyme. In native enzyme, pre-steady state kinetics show that the formation of the phosphoenzyme is partially sensitive to ADP while modification of the enzyme by pretreatment with 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB) in the absence of Mg2+ results in a steady-state phosphoenzyme population, a component of which is ADP sensitive. The ATP/ADP exchange reaction can be either stimulated or inhibited by the presence of K+ as a function of pH and Mg2+.

Adenosine Diphosphate↗
PubMed1982

Inhibition of acid secretion in isolated gastric glands by substituted benzimidazoles.

A new class of gastric acid inhibitors, substituted benzimidazoles (H 83/69 and H 149/94), have been tested in an isolated rabbit gastric gland preparation. Acid formation in the glands was stimulated by histamine, dibutyryl cAMP (DBcAMP), and high extracellular K+ concentrations, and the glandular secretory response was measured by changes in oxygen consumption and in accumulation of the weak base [14C]aminopyrine (AP). The substituted benzimidazoles inhibited AP accumulation induced by all stimulants in a dose-dependent noncompetitive manner. In contrast, cimetidine only inhibited histamine-induced AP accumulation. Basal AP accumulation, not affected by cimetidine, was also inhibited by the substituted benzimidazoles, as was the increase in glandular oxygen consumption produced by the addition of histamine and DBcAMP. Basal oxygen consumption was inhibited by about 15%. The substituted benzimidazoles, like AP, are weak bases and were also found to accumulate in the glands. Semiquantitative morphological studies of glands stimulated by histamine plus theophylline did not show any change in the enlarged secretory surface area after stimulation in the presence of inhibitory concentrations of H 149/94 (10(-4) M). The results suggest that substituted benzimidazoles have a mechanism of action different from that of H2-receptor antagonists and indicate a very distal site of action in the events leading to acid formation.

Aminopyrine↗
PubMed1981

The interaction of H+ and K+ with the partial reactions of gastric (H+ + K+)-ATPase.

The influence of H+ and K+ on the partial reactions and transport of gastric (H+ + K+)-ATPase was studied. Using transient kinetics, the effects and sidedness of effects of H+ and K+ on formation and breakdown of phosphoenzyme were determined in intact and lyophilized reconstituted vesicles in the absence and presence of gramicidin. Whereas increasing H+ concentrations on the ATP-binding face of the vesicles accelerates phosphorylation, increasing K+ concentrations inhibits phosphorylation. Increasing H+ on this side reduces K+ inhibition of the phosphorylation rate. At low ATP/K+ ratios, the phosphorylation step can become rate-limiting for steady state hydrolysis. Decreasing H+ accelerates dephosphorylation in the absence of K+. K+ on the internal or luminal face of the vesicles accelerates dephosphorylation, and this rate is reduced with increasing H+ concentrations. At low internal pH, K+-dependent dephosphorylation may become rate-limiting. H+ transport measurements using fluorescence quenching of acridine orange show that whereas internal K+ is required for H+ transport, external K+ inhibits the rate of formation of a pH gradient, and the inhibition is reduced by decreasing medium pH. The pH optimum for ATPase activity and transport correlated in the vesicles, and the K0.5 of K+ for transport correlated with data for intact parietal cells.

Adenosine Triphosphatases↗
PubMed1981

Substituted benzimidazoles inhibit gastric acid secretion by blocking (H+ + K+)ATPase.

Studies both in vivo and in vitro have shown that substituted benzimidazoles inhibit the stimulation of acid secretion produced by dibutyryl cyclic AMP and histamine. Furthermore, the results differ from those produced by H2 antagonists and anticholinergic agents in that the inhibition is not competitive, and the site of action is intracellular and peripheral to that of dibutyryl cyclic AMP. To investigate the biochemical mechanism of action of substituted benzimidazoles, one such compound, H 149/94 (2-([2-(3-methyl)pyridyl-methyl]-sulphinyl)-5-methoxycarbonyl-6-methylbenzimidazol), has been tested either directly on an (H+ + K+)ATPase isolated from pig and human gastric mucosa or on the function of this enzyme in gastric glands isolated from rabbit and human gastric mucosa. (H+ + K+)ATPase, which has only been found at the secretory surface of the parietal cell, catalyses a one-to-one exchange of protons and potassium ions. It is possibly the proton pump within the gastric mucosa, and may thus be the terminal or one of the terminal steps of the acid secretory process. We show here that H 149/94 inhibits (H+ + K+)ATPase, which may explain its inhibitory action on acid secretion in vitro and in vivo. Because of the unique distribution and properties of the (H+ + K+)ATPase, the inhibitory action of H 149/94 on this enzyme may be a highly selective clinical means of suppressing the acid secretory process.

2-Pyridinylmethylsulfinylbenzimidazoles↗