Interspecies comparison of the functional characteristics of plasma membrane monoamine transporter (PMAT) between human, rat and mouse

- We compared the functional characteristics of PMAT between human, rat and mouse.
- Similar to hPMAT, rPmat and mPmat function as a monoamine transporter, but not a nucleoside transporter.
- Similar monoamine affinities of PMAT/Pmat were observed between human, rat and mouse.
- In all three PMAT/Pmat expressing cell lines MPP+ transport was inhibited by decynium 22 and GBR12935 with inhibition potencies within the same order of magnitude.

Plasma membrane monoamine transporter (PMAT) is a newly discovered monoamine transporter belonging to the equilibrative nucleoside transporter family. Highly expressed in the brain, PMAT represents a major uptake2 transporter that may play a role in monoamine clearance. Although human PMAT has been functionally characterized at the molecular level, rodent models are often used to evaluate PMAT function in ex vivo and in vivo studies. The aim of this study was to examine if there is potential species difference in the functional characteristics of PMAT between human, rat and mouse. A set of transfected cells stably expressing human PMAT (MDCK/hPMAT), rat Pmat (MDCK/rPmat) and mouse Pmat (Flp293/mPmat) were constructed. In MDCK/hPMAT, MDCK/rPmat and Flp293/mPmat cells, cellular localization analyses revealed that hPMAT, rPmat and mPmat are expressed and mainly localized to the plasma membranes of cells. The uptake of MPP+, serotonin and dopamine by MDCK/hPMAT, MDCK/rPmat and Flp293/mPmat cells was significantly increased compared with those by the mock transfection control. In contrast, two nucleosides, uridine and adenosine, minimally interacted with PMAT/Pmat in all species. The hPMAT-, rPmat- and mPmat-mediated uptakes of MPP+, serotonin and dopamine were saturable, with Km values of 33.7 μM, 70.2 μM and 49.5 μM (MPP+), 116 μM, 82.9 μM and 231 μM (serotonin), and 201 μM, 271 μM and 466 μM (dopamine), respectively, suggesting similar substrate affinities between human and rodent PMAT/Pmat. The prototypical inhibitors, decynium 22 and GBR12935, also showed similar inhibition potencies between species. In conclusion, the present study demonstrated interspecies similarities in the functional characteristics of human and rodent PMAT/Pmat, which indicate a practical utility of rat and mouse animal models for further investigating and extrapolating the in vivo function of PMAT in humans.

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