The Mechanism of the Secretion of Acid by the Gastric Mucosa

Hollander (1934) and Gilman and Cowgill (1931) and others have shown that the acid secretion of the gastric mucosa is pure hydrochloric acid of concentration such that it is isotonic with the blood. In forming the acid secretion the cells of the gastric mucosa of dogs raise the hydrogen ion concentration from 5 X log , the hydrogen ion concentration of blood, to 0.17 M, the hydrogen ion concentration of the acid secretion. The chloride ion concentration is raised from 0.11 M in plasma to 0.17 M in the secretion. Osmotic work is done in raising the concentration of the two ions. The minimal amount of energy needed to do the work is equal to the free energy increase obtained in raising the concentration of the ions. The free energy change can be calculated by means of the equation used by Borsook and Winegarden (1931) in their calculation of the work of the kidney. It has been found that the gastric mucosa must expend a minimum of 772 small calories per liter of secretion in concentrating the hydrogen ions and a minimum of 48 small calories per liter in concentrating the chloride ions. Since the osmotic pressures of blood and gastric juice are the same the mol fraction of water in each is the same. Consequently no reversible work is done when water passes from the blood to the secretion, and no reversible energy is expended. A very small amount of irreversible work is done on the water in overcoming viscosity when water moves at a finite rate. The energy necessary to perform this work is doubtless derived from the difference in hydrostatic pressure between the blood and the gastric juice. Davenport (1939, 194Oa, 1940b) h as suggested that the mechanism of the secretion of acid is that expressed in figure 1. Some mechanism in the parietal cells whose rate of action is directly proportional to the rate of formation of carbonic acid in the cells secretes hydrogen ions and uses energy. The principle of electrical neutrality of solutions requires that exactly the same number of anions be present in the secretion as there are hydrogen ions. In order to satisfy the principle, chloride ions pass 165