Exchange diffusion of chloride in frog gastric mucosa

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Abstract
Chloride flux from nutrient to secretory surface of frog gastric mucosa was observed to be maximal with isotonic NaCl as the secretory solution, and was depressed in varying amounts by the replacement of NaCl with other sodium salts or nonelectrolytes. In particular, bicarbonate ion in the secretory solution lowered Cl flux, but not because of an increase in pH. On the contrary, increasing the partial pressure of CO2 to maintain a normal secretory pH produced a further decrease in Cl flux. This decrement was similar to that due to increasing CO2 pressure only, so that effects of bicarbonate ion and CO2 were additive. The largest reduction in Cl flux was found with nonelectrolytes in the secretory solution. According to a previous hypothesis, the different degrees of flux depression reflect different affinities of the replacement solute for a transport or exchange carrier substance in the mucosal membrane. Although a similar but smaller effect on Cl flux was found in cellulose membranes, the evidence indicates that the effect in the functioning gastric mucosa is not exclusively physico-chemical in origin.

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