The apical surface of canine chief cell monolayers resists H⁺ back-diffusion

Abstract

The resistance of the gastric mucosa to acid and peptic injury is reflected by a resistance to the back-diffusion of H⁺ from gastric lumen to blood^1,2. The nature of this ‘barrier’, however, remains undefined. Using Ussing chambers, we have now studied the acid-barrier function of monolayers prepared from dispersed canine fundic chief cells³. These monolayers secrete pepsinogen in response to stimulation⁴. We found that, on acidification of the apical solution to pH 2, transepithelial resistance (R) increased 2.6-fold and the monolayers maintained this 1:100,000 H⁺ concentration gradient for more than 4 h. The addition of aspirin to the acidified apical solution caused a rapid decay in R, as did acidification of the basolateral solution to a pH < 5.5. Ouabaintreated monolayers displayed the rise in R expected with apical acidification, while potential difference (V) and short-circuit current (I_sc) decreased essentially to zero, indicating impermeability to H⁺. However, if the integrity of the ouabaintreated monolayers was disrupted by low apical pH, H⁺ permeation occurred, reflected by an I_sc that was dependent on the H⁺ gradient across monolayers. These data indicate that the apical surface of chief cells is a very tight barrier to H⁺ diffusion and may be an important element resisting acid-peptic injury.