Gastric mucus of the guinea pig: proton carrier and diffusion
barrier.
Schreiber, S[diaeresis]oren, and Peter Scheid.
Institut f[umlaut]ur Physiologie, Ruhr-Universit[umlaut]at Bochum,
44780 Bochum, Germany
APStracts 3:0192G, 1996.
Proton transport with the gastric mucus was investigated in the guinea
pig in vitro using three experimental series. Series I: Using fine
-tipped double-barreled microelectrodes, pH-profiles were obtained in
the mucus and the mucosa of a gastric explant. With a luminal pH of
1.80, the pH increased across this layer to about 6 at the epithelial
surface. The thickness of the gastric mucus gel layer increased
continuously by 170 (+/- 100) [mu]m x h-1 in the unstimulated and by
450?(+/- 120) [mu]m x h-1 in the histamine-stimulated preparation
(mean +/- s.d.). Series II: Fresh guinea pig gastric mucus was
obtained from the gastric mucosa and titrated at 10 degrees C from pH
6.5 to 0.7, followed by an incubation period of 30?min at 37 degrees
C. During this in cubation period, a spontaneous acidic shift was
observed which corresponded to a proton release from the mucus of
130?(+/- 19) mmol x _-1. This proton release could be blocked by the
pepsin inhibitor pepstatin, and was not observed when titrating down
to only pH 3. The buffer values calculated as the mean slope of the
titration curves in the pH range of 7 to 3 averaged 40?mmol x _-1 x
pH-1. Series III: When titration was repeated with purified porcine
mucin, no proton release was observed during incubation at pH 1.0,
unless pepsinogen (375 units x ml-1) had been added before titration.
Proton release during incubation at pH 1.0 and 37 degrees C in the
presence of pep sinogen averaged 50?mmol x _-1. The data suggest that
protons secreted by the gastric mucosa are buffered by the
continuously secreted mucus and transported, bound to the proteins of
the mucus, towards the gastric lumen . During this transport,
pepsinogen is converted within the mucus to pepsin. Pepsin modifies
the buffering properties of the mucus, whereby protons are released
from the protein binding. Thus, the mucus forms a vehicle for proton
transport towards the gastric lumen, while at the same time
constituting a diffusion barrier to prevent proton back-diffusion
towards the gastric epithelium.
Received 8 September 1995; accepted in final form 3 September
1996.
APS Manuscript Number G396-5.
Article publication pending Am. J. Physiol. (Gastrointest. Liver
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 7 October 1996