Osmotic flow of water in isolated frog gastric mucosa.

A gravimetric procedure was used to measure net volume flow across bullfrog gastric mucosa mounted between chambers. A portion of the net volume flow towards the lumen was coupled to acid production. With an isotonic solution instilled on the luminal surface, the secreted acidity (ratio of increase in acid output to increase in volume flow) was hypertonic, in agreement with previous reports in mammalian stomach. Dilution of the secretory solution to 10% of normal nearly abolished the net volume flow coupled to acid production so that the mean secreted acidity rose to 1.87 M. Other experiments in which gastric juice was collected from this preparation showed that secretion into an initially empty lumen was only slightly hypertonic, as in mammalian stomach. The results indicate that instillation of secretory solution dilutes the endogenous osmotic gradient due to secreted HC1. This gradient is probably just outside the apical surface of the oxyntic cells of stomach.