The organic anion p-aminohippurate (PAH) is specifically secreted by the renal proximal tubule. The possibility was examined that the probenecid sensitive PAH transport system (which is involved in this secretory process in renal proximal tubule cells in vivo) is retained in primary cultures of rabbit kidney proximal tubule cells. Significant 3H-PAH uptake into primary cultures of proximal tubule cells was observed. After 10 min, 150 pmole PAH/mg protein had accumulated intracellularly. Given an intracellular fluid volume of 10 microliter/mg protein, the intracellular PAH concentration was estimated to be 15 microM. The initial rate of PAH uptake (when 50 microM PAH was in the uptake buffer) was inhibited 50% by 2 mM probenecid. Intact monolayers also exhibited Na+-dependent alpha methyl-D-glucoside uptake (an apical marker). Basolateral membranes were purified from primary rabbit kidney proximal tubule cell cultures. Probenecid sensitive PAH uptake into the membrane vesicles derived from the primary cultures was observed. The rate of PAH uptake was equivalent to that obtained with vesicles obtained from the rabbit renal cortex. No significant Na+-dependent D-glucose uptake into the vesicles was observed, indicating that primarily basolateral membrane vesicles had indeed been obtained.

The present investigation compares brush-border (BBM) and basolateral membrane (BLM) vesicles in terms of purity, function, appearance on sodium dodecyl sulfate (SDS) gels, and labeling pattern by use of N-(4-azido-2-nitrophenyl)-2-aminoethanesulfonic acid (NAP-taurine), a photoaffinity analogue of p-aminohippurate (PAH). Both BLM and BBM were vesicular by demonstration of PAH uptake into an osmotically active space and had probenecid-inhibitable uptake of PAH. Time courses for uptake were similar. 250 microM NAP-taurine resulted in a 35% inhibition of PAH uptake in BLM but it did not significantly effect PAH uptake into BBM. The latter was affected by 1 mM NAP-taurine. A comparison of Coomassie blue SDS gels of BLM and BBM showed markedly different staining patterns. A major band at approximately 52,000 daltons was more intensely stained in BLM than BBM. Major bands at approximately 40,000 and approximately 80,000 were stained more heavily in BBM than BLM. A minor protein at 26,000 in the BLM did not appear in BBM. An irreversible inhibition of PAH uptake in BLM was observed after photolysis in the presence of NAP-taurine. This was associated with the labeling of four protein bands on SDS polyacrylamide gels. In contrast no labeling was observed in BBM.

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Two stilbene derivates that had been used to covalently label the Cl- carrier in the erythrocyte were investigated for reactivity with the renal organic anion system. These compounds, 4,4'-diisothiocyanostilbene-2,2'-disulfonate (DIDS) and (4,4'-diisothiocyano)-dihydrostilbene-2,2'-disulfonate (H2DIDS), were found to be potent inhibitors (Ki congruent to 35 microM) of p-aminohippurate (PAH) transport in the renal cortical slice without affecting tetraethylammonium (TEA) transport or tissue viability. During renal clearance studies performed in the perfused kidney, DIDS decreased the PAH/inulin clearance ratio to congruent to 1. When the possible renal transport of [3H]H2DIDS was investigated, the renal slice transport or binding of [3H]H2DIDS reached a slice-to-medium ratio of congruent to 6, and this accumulation was decreased by probenecid. In perfused kidney experiments, the [3H]H2DIDS/inulin clearance ratio was congruent to 0.8. Since probenecid reduced this clearance ratio to congruent to 0.5, there was the possibility that H2DIDS underwent tubular secretion. In conclusion, DIDS and H2DIDS interacted with the renal organic anion transport system, which indicated that these compounds were possible probes for this transport system.

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