Local pH elevation mediated by the intrabacterial urease of Helicobacter pylori cocultured with gastric cells.
Level 5 - mechanism / opinion, no new human data
In vitro bench and cell-culture mechanistic study with no human clinical data.
PubMed 10930437 · doi:10.1172/JCI9351
What was done
Investigators evaluated the spatial and temporal dynamics of pH and intracellular calcium ([Ca2+]in) changes during Helicobacter pylori acid adaptation using an in vitro coculture model with human gastric AGS cells. They compared wild-type H. pylori to a nonpolar ureI-deletion mutant strain (ureI-ve). Measurements of bacterial periplasmic pH, cytoplasmic pH, medium pH, and AGS intracellular pH and calcium were conducted using pH- and Ca2+-sensitive fluorescent dyes with confocal microscopy following the addition of urea at pH 5.5, with or without detergent (C12E8) permeabilization or medium neutralization.
What was found
The abstract reports qualitative kinetics and directional changes without specific numerical values. In wild-type bacteria at pH 5.5, the addition of urea sequentially elevated bacterial periplasmic pH, then medium pH, and subsequently AGS cell intracellular pH. In contrast, ureI-deletion mutants showed no change in periplasmic pH and produced a slower increase in medium pH; membrane permeabilization with C12E8 restored rapid cytoplasmic and medium pH elevation. Perfusion of AGS cells with coculture medium at pH 5.5 did not alter intracellular pH or [Ca2+]in unless the conditioned medium was first neutralized to raise the NH3/NH4+ ratio.
Why it matters
This study demonstrates that the proton-gated urea channel UreI is required for intrabacterial urease to buffer the bacterial periplasm and resist low pH environments. It also indicates that host cell physiologic alterations driven by bacterial ammonia generation occur indirectly through ambient neutralization rather than direct injection via type IV secretion systems.
Limits
This is an entirely in vitro cell-culture and bench study lacking in vivo validation in animal models or human subjects. The abstract provides no exact quantitative values (such as baseline and final pH measurements, ion concentrations, or statistical significance metrics). AGS cells are an immortalized adenocarcinoma line that may not fully reflect native gastric epithelial physiology.
Cited by
- supports Helicobacter pylori is present in 80% of the population and releases alkaline ammonia to make its environment more alkaline.