Ion transport across the excised bullfrog lung

Fluxes of ions and water across the short-circuited, excised bullfrog lung were determined by radioisotope techniques. The unidirectional flows of Na+, K+, Ca++, TcO4 minus, HCO3 minus, gluconate, rho-aminohippurate, dinitrophenolate, SO4 equal to, and water were symmetrical. Both HCO3 minus fluxes were reduced by acetazolamide. In contrast, Cl minus, Br minus I minus, and SCN minus movement from serosa to mucosa exceeded the flux in the opposite direction. Net Cl minus transport followed the kinetics of a saturable process and was inhibited by dinitrophenol and hypoxia. These results indicate an active secretion of halide anions and SCN minus into the lumen. Attempts to demonstrate Br minus anatagonism of Cl minus transport were equivocal. Cl minus transport accounted for 50 percent minus of the early short-circuit current but after 90 min the two measurements were equal. Incubation of the lung in bicarbonate-free Ringer revealed unequal decreases in the H+ concentration of the bathing solutions. Net "base" addition to the serosal solution was reduced by prior removal of the blood from the pulmonary vasculature. Therefore, "base" release could not be localized to the epithelia. The Na+, K+, Ca++ and Cl minus composition of the lung tissue was unchanged over 3 h. Since tissue and, hence cell Cl minus is lower than the concentration in the bathing solution the Cl pump is probably located in the luminal border of the alveolar epithelial cell.