Passive permeability of salicylic acid in renal proximal S2 and S3 tubules
Chatton, J.Y.; Roch-Ramel, F.
Journal of Pharmacology and Experimental Therapeutics 256(3): 1112-1118
1991
ISSN/ISBN: 0022-3565 PMID: 2005576 Document Number: 384512
The role of nonionic diffusion in the transport of salicylic acid across rabbit proximal S2 and S3 segments was investigated using the in vitro isolated perfused tubule technique. The [14C] salicylic acid apparent reabsorptive permeability (P'lb, 10-5 cm/s) was measured at 19.degree.C with luminal solutions kept at different pH and bath maintained at pH 7.4. In S2 tubules, P'l-b was 25.0 .+-. 3.5 when luminal pH was 6.0; P'l-b decreased to 8.1 .+-. 1.4 and to 4.4 .+-. 1.2 at a luminal pH of 6.5 and 7.0, respectively. In S3 tubules, P'l-b was 17.6 .+-. 2.4, 5.3 .+-. 1.1 and 3.4 .+-. 1.1 at a luminal pH of 6.0, 6.5 and 7.0, respectively. There was a close correlation between between P'l-b and the calculated proportion of non-ionized salicylic acid present at each pH, indicating that only the nonionized molecule could diffuse in our conditions. We calculated the apparent permeability of nonionic salicylic acid and found 0.248 .+-. 0.032 cm/s for S2 and 0.176 .+-. 0.022 cm/s for S3 tubules. These calculated permeabilities were independent of pH.