Electrogenic HCl theory in light of effects of SCN- and Ba2+ on frog stomach

It has been previously shown that a) thiocyanate (15 mM) inhibits H+ secretion and increases the resistance and potential difference (PD) which is explained on the basis of separate electrogenic mechanisms for H+ and Cl- and b) barium (1 mM) added to the nutrient side produces a large increase in the resistance and little change in the H+ rate and PD, and the site of the increased resistance is the nutrient membrane of the tubular cells. In the present paper we show that a) with Ba2+ on the nutrient side, addition of thiocyanate to the secretory side decreases the H+ rate to about zero and also decreases the resistance; and b) if the site of the decrease in resistance is the secretory membrane of the tubular cells, in which the HCl is produced, then these findings would be contrary to the predictions on the basis of the electrogenic theory. However, the transmucosal resistance is a function of the resistance across the surface epithelial cells and the resistance of the secretory and nutrient membranes of the tubular cells. With a 79 mM K+ pulse technique, the findings indicate that the resistance of the secretory membrane increases, and the decrease in the resistance is due to changes in the resistance of the surface cells and/or the nutrient membrane of the tubular cells.