| 19357179 |
Lee WK, Reichold M, Edemir B, Ciarimboli G, Warth R, Koepsell H, Thevenod F: Organic cation transporters OCT1, 2, and 3 mediate high-affinity transport of the mutagenic vital dye ethidium in the kidney proximal tubule. Am J Physiol Renal Physiol. 2009 Jun;296(6):F1504-13. Epub 2009 Apr 8.
The positively charged fluorescent dyes ethidium (Et (+)) and propidium (Pr (2+)) are widely used as DNA and necrosis markers. Et (+) is cytotoxic and mutagenic. The polyspecific organic cation transporters OCT1 (SLC22A1), OCT2 (SLC22A2), and OCT3 (SLC22A3) mediate electrogenic facilitated diffusion of small (< or =500 Da) organic cations with broad specificities. In humans, OCT2 mediates basolateral uptake by kidney proximal tubules (PT), whereas in rodents OCT1/2 are involved. In mouse kidney, perfused Et (+) accumulated predominantly in the S2/S3 segments of the PT, but not Pr (2+). In cells stably overexpressing human OCTs (hOCTs), Et (+) uptake was observed with K (m) values of 0.8 +/- 0.2 microM (hOCT1), 1.7 +/- 0.5 microM (hOCT2), and 2.0 +/- 0.5 microM (hOCT3), whereas Pr (2+) was not transported. Accumulation of Et (+) was inhibited by OCT substrates quinine, 3-methyl-4-phenylpyridinium (MPP (+)), cimetidine, and tetraethylammonium (TEA (+)). For hOCT1 and hOCT2, the IC (50) values for MPP (+), TEA (+), and cimetidine were higher than for inhibition of previously tested transported substrates. For hOCT2, the inhibition of Et (+) uptake by MPP (+) and cimetidine was shown to be competitive. Et (+) also inhibited transport of 0.1 microM [(3) H] MPP (+) by all hOCT isoforms with IC (50) values between 0.4 and 1.3 microM, and the inhibition of hOCT1-mediated uptake of MPP (+) by Et (+) was competitive. In Oct1/2 (-/-) mice, Et (+) uptake in the PT was almost abolished. The data demonstrate that Et (+) is taken up avidly by the PT, which is mediated by OCT1 and/or OCT2. Considering the high affinity of OCTs for Et (+) and their strong expression in various organs, strict safety guidelines for Et (+) handling should be reinforced. |
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