Renal handling of phenol red. II. The mechanism of substituted phenolsulphophthalein (PSP) dye transport in rabbit kidney tubules in vitro.

Abstract

The uptake of various substituted phenolsulfophthalein dyes by cortical slices of rabbit kidney was studied in detail in order to obtain more information on the secretory system for organic anions. The rate of initial uptake of dyes and the accumulation after incubation for 2 h under aerobic conditions increased in the order: phenol red (PR) > bromophenol blue (BPB) > bromocresol green (BCG) > bromothymol blue (BTB), while the reverse order of uptake was observed under anaerobic conditions. There was no difference between the uptake of BTB under aerobic and anaerobic conditions. The accumulation of dyes under anaerobic conditions could be accounted for by binding to tissue constituents. In comparison with PR the substituted dyes interacted extensively with the 700 G (cell membranes) and cytosol fractions of renal homogenates. Low concentrations of the substituted dyes efficiently inhibited the accumulation of p-aminohippurate (PAH). The concentration of dye resulting in 50% inhibition of PAH accumulation (KI) agreed well with concentrations estimated to sustain 50% of maximal dye transport (KM). On this basis the affinity of the dyes for the transport system increases in the order: PR < BPB < BCG < BTB. Probenecid, 2,4-dinitrophenol, PAH, octanoate and succinate affected to a smaller extent the uptake and binding of BPB and BCG by renal tissue than that previously shown for PR. No inhibitory effect of these substances on the accumulation of BTB by kidney tissue was observed. The binding of PSP dyes by phospholipid vesicles (liposomes) and a representative binding protein, human serum albumin, exhibited close similarity to that of binding by renal tissue. Partition experiments involving octanol-water phases indicated that the hydrophobicity of the dyes increased in the order: PR < BPB < BCG < BTB. BTB, despite its inhibitory potency, is apparently not transported by the organic anion system. BPB and BCG are transported to a lesser extent, and interact more strongly with the transport system than does PR. The substituted dyes by virtue of hydrophobic interaction with the transport system reduce the movement of the mobile part of the transport system.