Interaction of mercapto‐containing sulfonates with human, rabbit and mouse orthologs of OAT1 and OAT3

Expressed in the basolateral membrane of renal proximal tubule, OAT1 and OAT3 are involved in the excretion of many anionic compounds. Although they have overlapping selectivities for some substrates, they display markedly distinct interactions with others. Here we probe the molecular descriptors that influence selectivity of OAT1 vs. OAT3, focusing on their interaction with analogs of 2,3‐dimercapto‐1‐propanesulfonate (DMPS) a clinically used chelator of heavy metals. The human, rabbit and mouse orthologs of OAT1 and OAT3 were each stably expressed in Chinese hamster ovary cells. For all 3 species, OAT1 had a high affinity for para‐aminohippurate (K t s of 6–30 μM), whereas OAT3 had a high affinity for estrone sulfate (K t s of 3–10 μM). In all 3 species, DMPS was a relatively high affinity inhibitor of both OAT1 (IC 50 s of 55–83 μM) and OAT3 (IC 50 s of 18–85 μM). The elimination of one of the DMPS thiol groups (3‐mercapto‐1‐propanesulfonate) resulted in a modest decrease in apparent affinity for OAT1 (IC 50 s increased to 150–200 μM), and a profound decrease in affinity for OAT3 (IC 50 s of 2100–2300 μM). Elimination of both thiol groups (1‐propanesulfonate) effectively eliminated interaction with both transporters (IC 50 s ≥ 2–4 mM). Interestingly, a small increase in hydrophobic bulk (i.e., 1‐butanesulfonate) markedly increased interaction with OCT1 (IC 50 s of 50–500 μM), but had virtually no effect on interaction with OAT3 (IC 50 s ≥ 5 mM). These data suggest that modest differences in the structure of OAT1 and OAT3, conserved across species, permit fine discrimination of structurally similar thiol‐containing sulfonates. (NIH DK58251, DK56224, HL07249)