Helicobacter pylori augments the acid inhibitory effect of omeprazole on parietal cells and gastric H(+)/K(+)-ATPase

Abstract

Background: In duodenal ulcer patients, intragastric acidity during omeprazole treatment is significantly lower before Helicobacter pylori eradication than after cure.

Aims: To determine if H pylori enhances the acid inhibitory potency of omeprazole in isolated parietal cells and on H(+)/K(+)-ATPase.

Methods: Rat parietal cells and pig gastric membrane vesicles enriched in H(+)/K(+)-ATPase activity were incubated with H pylori and the H pylori fatty acid cis 9,10-methyleneoctadecanoic acid (MOA), and the inhibitory effects of omeprazole on parietal cell acid production, H(+)/K(+)-ATPase enzyme activity, and ATPase mediated proton transport were assessed.

Results: In isolated parietal cells, H pylori and MOA increased the acid inhibitory potency of omeprazole 1.8 fold. H pylori did not affect the inhibitory potency of omeprazole on H(+)/K(+)-ATPase enzyme activity. In proton transport studies, H pylori (intact bacteria and sonicate) and MOA accelerated the onset of the inhibitory effect of omeprazole and enhanced the proton dissipation rate in response to omeprazole. H. pylori itself increased proton permeability at the vesicle membrane.

Conclusion: Our results show that H pylori augments the acid inhibitory potency of omeprazole in parietal cells and enhances omeprazole induced proton efflux rate from gastric membrane vesicles. We suggest that omeprazole unmasks the permanent effect of H pylori on proton permeability at the apical parietal cell membrane, which is counteracted in the absence of a proton pump inhibitor by a reserve H(+)/K(+)-ATPase capacity.

Figure 1

Effect of H pylori and cis 9,10-methyleneoctadecanoic acid (MOA) on the inhibitory action of omeprazole on dibuturyl cyclic adenosine monophosphate (dbcAMP) stimulated acid production in rat parietal cells. Gastric cells (2×10⁶ cells, parietal cell content 28-35%) were incubated without (untreated), or with H pylori (50 cfu/gastric cell) or MOA (5 µmol/l). Thereafter, H pylori was removed from the cells. Omeprazole was added to the cells and acid production was initiated by dbcAMP (0.1 mmol/l). After 40 minutes of incubation at 37°C, intracellularly trapped aminopyrine was counted. dbcAMP stimulated aminopyrine uptake in untreated, H pylori, and MOA treated cells was 115 (37), 117 (40), and 124 (12) pmol aminopyrine/10⁵ parietal cells, respectively. These values were set to 100%. Values are mean (SEM) of four cell preparations. C, control. *p<0.05 v omeprazole alone.

Figure 2

Effect of H pylori on the inhibitory effect of omeprazole on gastric H⁺/K⁺-ATPase activity. Gastric membrane vesicles were incubated without (untreated) or with H pylori 5×10⁵ or 2.5×10⁶ bacteria/µg membrane protein. Bacteria were then separated from the medium. Omeprazole was added to the vesicles and ATPase activity was initiated by adding ATP and the K⁺ ionophore valinomycin. Values are mean (SEM). C, control.

Figure 3

Effect of omeprazole on H⁺/K⁺-ATPase mediated H⁺ transport in gastric membrane vesicles exposed to H pylori cells. Gastric vesicles (60 µg protein/ml) were incubated with and without H pylori (8×10⁵ bacteria/µg membrane protein) in 2 ml of 10 mmol/l piperazine-N,N'-bis [2-ethane-sulphonic acid]/Tris buffer containing 2 mmol/l MgCl₂ and 150 mmol/l KCl. After 30 minutes of incubation, H pylori was separated by centrifugation. Acridine orange and omeprazole (10 µmol/l) were added and proton transport was initiated by adding ATP and valinomycin (arrow).

Figure 4

Effect of omeprazole on H⁺/K⁺-ATPase mediated H⁺ transport in gastric membrane vesicles exposed to H pylori cells. Gastric membrane vesicles were incubated with H pylori (1.6 and 8×10⁵ bacteria/µg membrane protein) as described in fig 2. Proton transport was initiated by addition of ATP and valinomycin (arrow) and omeprazole was added (↑) when the pH gradient had reached its maximum value.

Figure 5

Effect of omeprazole on H⁺/K⁺-ATPase mediated H⁺ transport in gastric membrane vesicles exposed to a H pylori sonicate (1.6×10⁵ sonicated bacteria/µg membrane protein), cis 9,10-methyleneoctadecanoic acid (MOA) (1 and 5 µmol/l), and tetradecanoic acid (10 µmol/l). Experimental conditions were as described in fig 2. Proton transport was initiated by addition of ATP and valinomycin (arrow) and omeprazole was added (↑) when the pH gradient had reached its maximum value.

Figure 6

Effect of the magnesium chelating agent ethylenediaminetetraacetic acid (EDTA) on intravesicular acidity in gastric membrane vesicles treated with and without H pylori cells (8×10⁵ and 1.6×10⁶ bacteria/µg membrane protein). Experimental conditions were as described in fig 2. Proton transport was initiated by addition of ATP and valinomycin (arrow) and EDTA was added (↑) to stop the ATPase reaction when the pH gradient had reached its maximum value.