Active transport of ions by the gastric mucosa of the rabbit foetus

1. The short‐circuit current and absolute fluxes of Na + and Cl − across the gastric mucosa of the 28‐day rabbit foetus have been measured in vitro . 2. Substitution of Na + in the solution bathing the mucosal surface by choline ion or K + resulted in a 70% decrease in short‐circuit current which was reversed when Na + was restored to the mucosal solution. The portion of the short‐circuit current dependent on the presence of Na + in the mucosal solution was found to be equivalent to the net flux of Na + from mucosa to serosa. 3. The net flux of Cl − from serosa to mucosa was compared with the short‐circuit current persisting when Na + had been replaced in the mucosal solution. Averaged results from sixteen experiments indicated that the net flux of Cl − was equivalent to 166% of the Na + independent short‐circuit current. 4. The results indicated that the component of short‐circuit current associated with acid secretion was independent of the presence of Na + in the mucosal solution. 5. The small scale of the experiments and the secretion of mucus by the preparation did not permit successful simultaneous measurement of H + secretion and short‐circuit current. 6. Replacement of Cl − by SO 4 2- or glucuronate in the solutions on both sides did not result in a reversal or decrease in magnitude of the Na + independent short‐circuit current, even after allowing time for the tissue to become depleted of Cl − . It is suggested that a non‐specific active anion transport was occurring.