Origins of positive potential difference of frog gastric mucosa in Cl--free solutions.

Experiments were performed on gastric mucosae of Rana pipiens with an in vitro method. Bathing both sides of the mucosae in Cl--free solutions resulted in an inverted potential difference (PD) (i.e., nutrient negative). Cimetidine in a concentration of 10(-4) or 10(-3) M in the nutrient solution gave a positive PD when the H+ secretory rate was zero or near zero and confirmed that the PD versus H+ rate was linear. the origins of the positive PD were examined by ion replacement, e.g., choline for Na+ in both solutions. When both solutions had 25 mM HCO(-)3 (i.e., no HCO(-)3 gradient), the difference in PD between choline sulfate and Na2SO4 solutions indicated a possible small active transport of Na+ from the secretory to nutrient side. Similar experiments indicated no active K+ transport. A residual PD occurred without Na+. With H+ rate zero, 100% O2, and no HCO(-)3, a base secretion of about 0.4 mueq.h-1.cm-2 was obtained in a direction to contribute to the positive PD. Active SO2(-)4 transport may occur.