Comparison of uptake and binding of disodium cromoglycate and phenol red in rat lung

In rat lung slices 3H-disodium cromoglycate (3H-DSCG) (0.001 mM) was taken up rapidly and 3H-DSCG tissue spaces, which equilibrated by 30 minutes, remained constant over a 4-hour incubation period. In contrast, 35S-phenol red (0.001 mM) accumulated in lung slices to a much greater extent than did DSCG, and the measured tissue spaces continued to increase over a 3-hour incubation period. In the presence of either phenol red (1 mM) or the metabolic inhibitors, iodoacetic acid (10(-4) M) and dinitrophenol (10(-4) M), 3H-DSCG uptake was significantly decreased. Accumulation of 3H-DSCG in lung slices and binding to tissue homogenates (pH 7.4) was also decreased when Ca and Mg ions were omitted from the bathing solution. Although DSCG and phenol red mutually inhibited the accumulation of one another over time in lung slices and 3H-DSCG (0.001 mM) binding to lung homogenates was decreased in the presence of 1 mM phenol red, 35S-phenol red efflux was not altered by the addition of 1 mM DSCG during the washout. Thus, it appears that, in rat lung, DSCG and phenol red share a common binding site(s) for uptake, possible on the transport "carrier." Also, there appear to be additional pulmonary binding sites for phenol red. These sites are not occupied by DSCG and their presence could account for the differences observed in the extent of accumulation of the two compounds in lung slices.