Transport of asymmetric dimethylarginine (ADMA) by cationic amino acid transporter 2 (CAT2), organic cation transporter 2 (OCT2) and multidrug and toxin extrusion protein 1 (MATE1)

Asymmetric dimethylarginine (ADMA), inhibiting the nitric oxide (NO) synthesis from l-arginine, is a known cardiovascular risk factor. Our aim was to investigate if ADMA and/or l-arginine are substrates of the human cationic amino acid transporters 2A (CAT2A, SLC7A2A) and 2B (CAT2B, SLC7A2B), the organic cation transporter 2 (OCT2, SLC22A2), and the multidrug and toxin extrusion protein 1 (MATE1, SLC47A1). We systematically investigated the kinetics of ADMA and l-arginine transport in human embryonic kidney (HEK293) cells stably overexpressing CAT2A, CAT2B, OCT2, or MATE1. Vector-only transfected HEK293 cells served as controls. Compared to vector control cells, uptake of ADMA and l-arginine was significantly higher (p < 0.05) in cells expressing CAT2B and OCT2 at almost all investigated concentrations, while cells expressing CAT2A only showed a significant uptake at concentrations above 300 mu M. Uptake of MATE1 overexpressing cells was significantly (p < 0.05) higher at pH 7.8 and 8.2 than controls. Apparent V (max) values (nmol mg protein(-1) min(-1)) for cellular uptake of ADMA and l-arginine were a parts per thousand 11.8 +/- A 1.2 and 19.5 +/- A 0.7 for CAT2A, a parts per thousand 14.3 +/- A 1.0 and 15.3 +/- A 0.4 for CAT2B, and 6.3 +/- A 0.3 and > 50 for OCT2, respectively. Apparent K (m) values (mu mol/l) for cellular uptake of ADMA and l-arginine were a parts per thousand 3,033 +/- A 675 and 3,510 +/- A 419 for CAT2A, a parts per thousand 4,021 +/- A 532 and 952 +/- A 92 for CAT2B, and 967 +/- A 143 and > 10,000 for OCT2, respectively. ADMA and l-arginine are substrates of human CAT2A, CAT2B, OCT2 and MATE1. Transport kinetics of CAT2A, CAT2B, and OCT2 indicate a low affinity, high capacity transport, which may be relevant for renal and hepatic elimination of ADMA or l-arginine.