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)

Abstract

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 300μM. Uptake of MATE1 overexpressing cells was significantly (p<0.05) higher at pH 7.8 and 8.2 than controls. Apparent V max values (nmolmg protein(-1)min(-1)) for cellular uptake of ADMA and L-arginine were ≈11.8±1.2 and 19.5±0.7 for CAT2A, ≈14.3±1.0 and 15.3±0.4 for CAT2B, and 6.3±0.3 and >50 for OCT2, respectively. Apparent K m values (μmol/l) for cellular uptake of ADMA and L-arginine were ≈3,033±675 and 3,510±419 for CAT2A, ≈4,021±532 and 952±92 for CAT2B, and 967±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.