Effects of ammonium ion and ammonia on function and morphology of in vitro frog gastric mucosa
Yanaka, A.; Muto, H.; Ito, S.; Silen, W.
American Journal of Physiology 265(2 Pt 1): G277-G288
1993
ISSN/ISBN: 0002-9513 PMID: 8368311 Document Number: 422054
The effects of ammonium ion (NH-4+) and ammonia (NH-3) on function and morphology of gastric epithelial cells were studied in intact sheets of in vitro frog (Rana catesbeiana) gastric mucosa. Luminal 115 mM NH-4Cl at luminal pH 8.0 (calculated (NH-3) 2.7 mM), but not at 5.0 (calculated (NH-3) 3 mu-M) induced 1) an increase in intracellular pH (pH-i) in oxynticopeptic cells (OPC) and decreases in transmucosal potential difference (PD) and electrical resistance (R) in resting tissues, 2) a decrease in histamine-stimulated H+ secretion and an increase in H+ backdiffusion after removal of luminal NH-4Cl, and 3) augmented acidification of OPC during luminal acidification. Serosal 30 mM NH-4Cl at serosal pH 7.2 (calculated (NH-3) 0.47 mM) induced 1) an increase in pH-i in OPC and inhibition of the alkalinization of OPC after removal of ambient Cl-, 2) a decrease in PD associated with the increase in R and decrease in short-circuit current, effects attenuated by serosal 15 mM K+, accentuated by 0.2 mM Ba-2+, and abolished by removal of ambient Cl-, 3) a sudden drop of PD in resting, but not in stimulated tissues, effects prevented by high serosal pH (7.8), serosal HCO-3-, or removal of luminal Cl-, 4) a decrease in histamine-stimulated H+ secretion and an increase in H+ backdiffusion after removal of NH-4Cl, and 5) augmented acidification of OPC during luminal acidification. These results suggest that 1) luminal NH-3, but not NH+, increases backdiffusion of H+ from the lumen to the mucosa, 2) serosal NH-3 and/or NH-4+ induces depolarization of OPC and decreases electrogenic Cl- transport, thereby attenuating the activity of the basolateral Cl--HCO-3- exchanger in OPC, and 3) both of these effects contribute to the augmented acidification of OPC during exposure to high luminal (H+).