CHARACTERIZATION OF L-ARGININE TRANSPORT BY PULMONARY-ARTERY ENDOTHELIAL-CELLS

The transport of L-arginine by porcine pulmonary artery endothelial cells (PAECs) was characterized. Uptake of 50 muM L-arginine was time dependent and linear in the presence and absence of sodium, with approximately 70% of uptake occurring via a carrier-mediated Na+-independent process. Kinetic studies of saturable Na+-independent transport revealed two transport components: a high-affinity transporter [Michaelis constant (K(m)) = 304 +/- 23 muM, maximal transport velocity (V(max)) = 679 +/- 34 pmol . mg protein-1 .30 s-1], and a low-affinity carrier (K(m) = 3.9 +/- 1.0 mM, V(max) = 2.8 +/- 0.7 nmol/mg protein-1 .30 s-1). Saturable Na+-independent uptake of 50 muM L-arginine transport showed no significant variation in uptake between pH 6.0 and 8.0 and was blocked by the system y+ substrates L-arginine, L-homoarginine, L-lysine, and L-ornithine. Na+-dependent L-arginine transport occurred via a single high-affinity system (K(m) = 62 +/- 3 muM, V(max) = 211 +/- 24 pmol . mg protein- 1 .30 s-1) which was significantly inhibited by L-arginine, L-lysine, L-ornithine, L-leucine, L-alanine, L-CYSteine, and L-glutamine, but not by 2-methylaminoisobutyric acid. Na+-dependent arginine uptake was pH and hormone insensitive, and lithium did not substitute effectively for sodium. These data are consistent with mediation of high-affinity arginine transport by PAECs via Na+-independent system y+ and Na+-dependent system B(O,+).