Accumulation of [14C]urate and [3H]PAH in isolated proximal tubular segments of the rabbit kidney

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Abstract
Segments of rabbit proximal tubules (S1, S2 and S3) were incubated (30 min, 37.degree. C, pH 7.4) in Ringer solution (under O2) containing [14C]urate or [3H]PAH [p-aminohippurate] and probenecid, pyrazinoic acid (PZA), urate or PAH at 1 mM. The ratio [14C]urate (cpm/nl of tubular cell H2O)/cpm per nl of incubation medium) (T/M) reached 2.92 .+-. 0.31 (mean .+-. SE; n = 15), 6.08 .+-. 0.42 (n = 42) and 1.72 .+-. 0.31 (n = 14) for S1, S2 and S3 segments, respectively. In these segments, the uptake of [3H]PAH was 22.7 .+-. 4.6 (n = 19), 133 .+-. 18.9 (n = 24) and 66.2 .+-. 15.3 (n = 20). The accumulation of [14C]urate was saturated at 2 .times. 10-4 M in the medium and that of [3H]PAH at 7 .times. 10-5 M in the medium. Secretory transport was saturated at the same bath PAH concentration in perfused tubules. Urate and PAH transports inhibited each other, suggesting a common transport mechanism located in the S2 segment. Probenecid was a strong and PZA a weak inhibitor of this transport system.