OCT2 and MATE1 Provide Bidirectional Agmatine Transport

Agmatine is a biogenic amine (L-arginine metabolite) of potential relevance to several central nervous system (CNS) conditions. The identities of transporters underlying agmatine and polyamine disposition in mammalian systems are not well-defined. The SLC-family organic cation transporters (OCT) OCT1 and OCT2 and multidrug and toxin extrusion transporter-1 (MATE 1) are transport systems that may be of importance for the cellular disposition of agmatine and putrescine. We investigated the transport of [H-3]agmatine and [H-3]putrescine in human ambryonic kidney (HEK293) cells stably transfected with hOCT1, hOCT2, and hMATE1. Agmatine transport by hOCT1 and hOCT2 was concentration-dependent, whereas only hOCT2 demonstrated pH-dependent transport. hOCT2 exhibited a greater affinity for agmatine (K-m = 1.84 +/- 0.38 mM) than did hOCT1 (K-m = 18.73 +/- 4.86 mM). Putrescine accumulation was pH- and concentration-dependent in hOCT2-HEK cells (K-m = 11.29 +/- 4.26 mM) but not hOCT1-HEK cells. Agmatine accumulation, in contrast to putrescine, was significantly enhanced by hMATE1 overexpression, and was saturable (K-m = 240 31 mu M; V-max = 192 +/- 10 pmol/min/mg of protein). Intracellular agmatine was also trans-stimulated (effluxed) from hMATE1-HEK cells in the presence of an inward proton-gradient. The hMATE1-mediated transport of agmatine was inhibited by polyamines, the prototypical substrates MPP+ and paraquat, as well as guanidine and arcaine, but not L-arginine. These results suggest that agmatine disposition may be influenced by hOCT2 and hMATE1, two transporters critical in the renal elimination of xenobiotic compounds.