Coupling of water to solute movement in isolated gastric mucosa

Osmosis is apparently the mechanism responsible for the coupling of water to solute transport in biological membranes. Often a secreted or absorbed fluid is essentially iso-osmotic with the solution of origin, or with plasma, and various models have been constructed by Curran, Diamond and others to account for such observations. More information is needed, however, to test further the predictions of these models and to facilitate correlation with known structural details. This study deals with gastric secretion and the effects of the luminal solution on its composition. Although pure gastric juice collected in vivo is virtually iso-osmotic with plasma, Teorell, Obrink and others found that instillation of a buffer solution (glycine) in the lumen led to a twofold increase in the concentration of gastric acid. This effect is not restricted to buffer solutions: the normality of H+ secreted into an isotonic (120 mM) NaCl solution bathing the isolated bullfrog gastric mucosa was 276 +/- 19 mmol/1 (13 experiments). Clearly the luminal solution affects the concentration of gastric secretion, probably by reducing an endogenous osmotic gradient. Thus the sites responsible for transport of H+ must be accessible from the luminal solution.