Renal handling of phenol red. I. A comparative study on the accumulation of phenol red and p-aminohippurate in rabbit kidney tubules in vitro.

1. The characteristics of renal accumulation of phenol red and p-aminohippurate (PAH) by slices of rabbit kidney cortex suspended in an electrolyte medium have been compared.2. It has been found that at low medium concentrations the accumulation of phenol red is about 4-5 times as high as that of PAH. Furthermore, phenol red is accumulated by the renal tissue under anaerobic conditions, in contrast to PAH.3. Experiments involving incubation of slices at low temperatures and addition of various metabolic inhibitors to the medium, indicate that the anaerobic accumulation of phenol red is due to binding to cellular constituents. This conclusion is corroborated by studies on renal homogenates from which it appears that phenol red is bound predominantly to the microsomal and mitochondrial fraction.4. The aerobic accumulation of phenol red is less susceptible to inhibition by probenecid, 2,4-dinitrophenol (DNP), and octanoate than is that of PAH. Besides, probenecid, DNP, and octanoate inhibit phenol red binding to the microsomal fraction, whereas mitochondrial binding of phenol red is unaffected by the presence of these substances.5. Fumarate and succinate affect the aerobic accumulation of phenol red and PAH to the same degree. Furthermore, fumarate, succinate, and PAH do not alter anaerobic accumulation of phenol red.6. It is concluded that probenecid, DNP, and octanoate cause more inhibition of organic anion transport than fumarate, succinate, and PAH because of lipophilic interaction with the membrane. The pronounced resistance of phenol red accumulation to inhibition by lipophilic inhibitors is probably due to the ability of the indicator dye to displace these substances from binding sites on the transporting membranes.