Electroneutral Acid Secretion in Frog Gastric Mucosa: An Electron Microprobe Analysis
To elucidate the mode of H secretion in the intact gastric mucosa, the cellular element concentrations and Rb uptake by individual surface and oxyntic cells of the short-circuited isolated frog gastric mucosa (Rana esculenta, Rana temporaria) were determined using electron microprobe analysis. The H secretion rate was measured by the pH stat method. Under normal conditions both surface and oxyntic cells exhibited typical cellular electrolyte patterns with low Na and high K concentrations. The apical parts of surface cells, in which large mucus-containing vesicles are located, were characterized by relatively high S and Ca concentrations. Histamine-stimulated H secretion in the gastric mucosa of R. esculenta and R. temporaria was about 2.0 and 0.5 µmol/cm2·h, respectively. In the presence of 20 mM Rb in the mucosal bathing solution, a substantial portion of cellular K was exchanged for Rb in oxyntic but not in surface cells. This K-Rb exchange was almost completely abolished by inhibition of H secretion with omeprazole indicating a specific H-Rb(K) exchange across the apical membrane of oxyntic cells. At a low H secretion of about 0.5 µmol/cm2·h about 70% of the H secretion rate could be matched by the omeprazole-inhibitable Rb uptake rate. Accordingly H secretion seems to be accomplished by an electroneutral H-Rb(K) exchange. The negligible Rb uptake into oxyntic cells at a mucosal Rb concentration of 5 mM might be explained by K recirculation across the mucosal membrane via a K conductance and the H-K-ATPase.