Uptake of [3H]PAH and [14C]urate into isolated proximal tubular segments of the pig kidney

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Abstract
Segments of proximal convoluted (PCT) and proximal straight (PST) tubules of minipigs and normal-sized pigs were microdissected (without collagenase treatment) and incubated (30 min, 37.degree. C, pH 7.4) in Ringer solution (under O2) containing [3H]PAH (p-aminohippurate, 3.10-5 M) or [14C]urate (9.10-5 M) and, in inhibitor studies, probenecid, pyrazinoic acid (PZA), urate, or PAH, all at 1 mM. In both strains the uptake of [3H]PAH expressed as mean T/M ratio (cpm/ml tissue water/cpm per ml incubation medium) was significantly higher (P < 0.001) in PCT than in PST. T/M was 34.7 .+-. 5.6 (SE) in 34 PCT and 2.4 .+-. 0.3 in 24 PST of 8 minipigs. In 2 normal-sized pigs the T/M was 14.1 .+-. 3.6 in 15 PCT and 1.4 .+-. 0.1 in 6 PST. Similar results were obtained for [14C]urate. In 8 minipigs the T/M was 4.9 .+-. 0.5 in 24 PCT and 2 .+-. 0.2 in 25 PST. In normal-sized pigs the T/M was 3.8 .+-. 0.3 in 35 PCT (5 pigs) and 1.9 .+-. 0.4 in 8 PST (2 pigs). In inhibitor studies urate significantly depressed the uptake of [3H]PAH, and unlabeled PAH depressed the uptake of [14C]urate. PZA significantly inhibited the uptake of [14C]urate but not that of [3H]PAH, whereas probenecid had a strong inhibitory effect on the uptake of both compounds. Apparently, [14C]urate and [3H]PAH are transported by a transport system located mainly in the proximal convoluted tubule. These findings are in contrast to the findings obtained in rabbits in which the transport system of PAH and urate is mainly located in the proximal part of the pars recta.