HYPOXIA INHIBITS L-ARGININE UPTAKE BY PULMONARY-ARTERY ENDOTHELIAL-CELLS

Under physiological conditions, L-arginine transport by porcine pulmonary artery endothelial cells (PAEC) is mediated by system y(+), a sodium-independent transport system that accounts for 60 +/- 5% of L-arginine transport, and system B-o,B-+, a sodium-dependent system that accounts for 40 + 5% of transport. Because NO production is dependent on intracellular L-arginine content and intracellular L-arginine content depends on transport of extracellular L-arginine, we examined the effect of hypoxia on L-arginine transport and intracellular L-arginine content in PAEC. Exposure of passage 3-7 PAEC in monolayer culture to 0% 0(2) for 4 h decreased L-arginine transport via system y(+) from 120 +/- 10 to 81 +/- 23 (in pmol . mg protein(-1) . 30 s(-1)) (P < 0.001), whereas 20-h exposures decreased transport from 122 +/- 17 to 84 +/- 18 (P < 0.001) in system y(+) and from 104 +/- 19 to 90 +/- 26 (P < 0.05) in system B-o,(+). Exposure to 5% Oz for 3-5 wk decreased L-arginine transport via system y(+) from 128 +/- 15 to 73 +/- 13 (P < 0.001) and via system B-o,(+) from 105 +/- 25 to 65 +/- 13 (P < 0.001). Kinetic studies revealed that hypoxia decreased the maximal transport velocity but not the apparent Michaelis constant for both system y(+) and system B-o,B-+, and the decreases in transport were not reversible after return to normoxia for up to 24 h. Long-term exposure, i.e., 3-5 wk, to 5% O-2 also resulted in decreases in intracellular L-arginine content (0.75 +/- 0.10 vs. 0.49 +/- 0.09 nmol/10(6) cells, P < 0.05) which did not reverse after return to normoxia for 24 h. Reductions in L-arginine uptake may impair NO production by hypoxic pulmonary endothelium by decreasing the availability of intracellular L-arginine.