Interaction of the Metal Chelator 2,3-Dimercapto-1-propanesulfonate with the Rabbit Multispecific Organic Anion Transporter 1 (rbOAT1)

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Abstract
The metal chelator DMPS (2,3-dimercapto-1-propanesulfonate) is used to treat heavy metal intoxication because it increases renal excretion of these toxins, which are accumulated in proximal tubule cells. To evaluate the involvement of the organic anion transporter 1 (OAT1) in the renal flux of DMPS, we examined the effect of DMPS on transport mediated by the rabbit ortholog of OAT1 and compared these characteristics with those observed in intact isolated rabbit proximal tubules. The rabbit OAT1 (rbOAT1) cDNA consisted of 2124 base pairs encoding a protein of 551 amino acids. Heterologous expression in COS-7 cells revealed rbOAT1-mediated transport ofp-aminohippurate (PAH; Kt = 16 μM). A 1 mM concentration of unlabeled PAH, α-ketoglutarate, urate, or probenecid inhibited [3H]PAH uptake by 70 to 90%.cis-Inhibition and trans-stimulation experiments using several Krebs cycle intermediates implicated α-ketoglutarate as the main intracellular exchange anion. Reduced DMPS inhibited rbOAT1-mediated fluorescein transport with an apparentKi of 102 μM. These characteristics paralleled those observed in isolated rabbit proximal tubules. PAH was transported into nonperfused single proximal tubule S2segments with a Kt of 76 μM. DMPS inhibited FL uptake into single tubule segments with aKi-app of 71 μM. Fluorescein efflux from preloaded tubules was trans-stimulated by 1 mM PAH and 1 mM DMPS, consistent with DMPS entry into tubule cells by rbOAT1. In summary, rbOAT1 mediates basolateral uptake of DMPS into proximal tubule cells, implicating this process in the detoxification process of heavy metals in the kidneys.