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Abstract
The gastric mucosa is covered by a continuous layer of bicarbonate-containing mucus
gel; the question arises how acid, formed in the gastric glands, moves into the lumen.
The pH in the gastric mucus gel and gel thickness were measured in anesthetized rats
with pH-sensitive microelectrodes (tip diameter, 1-5 microns).
During pentagastrin (40 micrograms.kg-1.h-1) stimulation of acid secretion, the pH
was higher in the gel than in the lumen (pH 2) up to a distance of 115 +/- 18 microns
from the epithelial surface and maximal (pH 7.2 +/- 0.1) at the surface. A similar
pH gradient was recorded at luminal pH 3. After omeprazole (10 mumol/kg) inhibition
of endogenous acid secretion and with exogenous acid in the lumen, the pH profile
was broader: 204 +/- 26 microns at luminal pH 2 and 231 +/- 63 microns at luminal
pH 3. In contrast, the pH at the epithelial surface was lower (pH 6.8-6.9). The gel
thickness (200-300 microns) was similar in all groups.
The significantly higher surface pH in acid-secreting stomachs probably reflects better
availability of interstitial mucosal bicarbonate. Bulk transport of secreted acid
in channels created by the gland luminal hydrostatic pressure may additionally act
to limit acidification of the mucus gel.