Phenol red absorption from the rat lung: Evidence of carrier transport

Abstract To investigate the absorption of [ 35 S]phenol red from the rat lung, 0.1 ml of Krebs-Ringer phosphate solution (pH 7.4) containing the compound was administered to anesthetized animals by way of a catheter introduced through a tracheal cannula. After various times, the lungs were removed and assayed for the amount of dye that remained. Studies with 0.01–1 mmol concentrations of phenol red indicated that pulmonary absorption of this anion occurred in part by a saturable, carrier-type transport process and in part by diffusion. Carrier transport became saturated at phenol red concentrations greater than 0.7 mmol, and the transport maximum was estimated to be at least 1.2 μg/ hour. Transport was inhibited by other sulfonic acid dyes and also by benzylpenicillin and cephalothin. The diffusion component of phenol red absorption was in close accord with the rate predicted from the molecular size and diffusion coefficient of the compound. The results indicate that the respiratory tract epithelium, like certain other body membranes, possesses a specialized process for the transport of certain organic anions.