ACTIVE-TRANSPORT OF PHENOL RED BY RAT LUNG SLICES

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Abstract
35S-phenol red was taken up by rat lung slices incubated in oxygenated Krebs-Ringer phosphate-glucose solution (pH 7.4) at 37.degree. C by a process showing the characteristics of active transport. Uptake against a concentration gradient occurred by a saturable process that was inhibited by low temperature, anaerobic conditions and certain metabolic inhibitors. Phenol red uptake was depressed in the presence of certain anionic dyes, such as chlorphenol red, bromphenol blue, bromthymol blue and bromcresol green and by various other organic acids, including disodium cromoglycate, probenecid, cephalothin and benzylpenicillin. In contrast isoniazid and p-aminohippuric acid had no effect on phenol red uptake, suggesting that a specificity exists in the rat lung for transport of anionic compounds. In the presence of paraquat, an organic cation, phenol red uptake increased. The extent of uptake of phenol red by lung slices depended on levels of Na, K and Ca ion in the incubation medium and on the thickness of the tissue slice. Phenol red was bound to lung homogenates; however, the characteristics of the binding were such that binding alone could not account for accumulation by lung slices.

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