Basic-alimentary tractRegulated alkali secretion acts in tandem with unstirred layers to regulate mouse gastric surface pH☆
Section snippets
Animal preparation
The surgical preparation for mice has been described previously.9 Briefly, the stomachs of anesthetized mice were exteriorized and everted to expose the gastric mucosa. The mouse was placed supine on the stage of an inverted confocal microscope (LSM 510; Zeiss, Jena, Germany) such that a portion of the exposed mucosa protruded into a perfusion chamber. The perfusion chamber and stage were warmed to keep the animal’s body temperature at 37°C.
Cl-NERF pH imaging
The protocol for imaging the mouse gastric surface pH
Results
In previous confocal microscopy measurements of gastric surface pH in rats and mice, results showed that surface pH remained at a near-constant value (pH 3.9–4.2) despite a dramatic conversion of the tissue secretions from alkali to acid when luminal pH was increased.5, 9 Our goal was to learn why surface pH was nearly constant around pH 4.
Discussion
This study investigated the physical basis for the pH gradient maintained at the gastric mucosal surface. Using in vivo confocal microscopy, we examined the influence of restricted diffusion, the unstirred layer, and juxtamucosal pH buffering on surface pH control. This technique also allowed us to compare results in the absence vs. presence of surface mucus.
This study is in agreement with previous work suggesting the presence of an unstirred layer at the gastric surface that limits entry or
Acknowledgements
We are grateful to Oleg Gerasimenko (Department of Medicine, University of Liverpool, UK) for his generosity in helping us with the uncaging experiments and George Sachs (Department of Physiology, University of California, Los Angeles) for his helpful urging to do the pH 2 experiments.
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Supported by the National Institutes of Health (Grant RO1DK 54940) and the American Heart Association (predoctoral fellowship; H.K.B.).