Selective stimulation of L-arginine uptake contributes to shear stress-induced formation of nitric oxide

The aim of this study was to investigate the kinetics of L-arginine transpo rt mechanisms and the role of extracellular L-arginine in nitric oxide form ation during shear stress activation of endothelial cells. Porcine aortic e ndothelial cells were grown to confluence and were exposed to various amoun ts of shear stress for 40 min. Formation of nitric oxide was monitored by m easuring elevation of endothelial cGMP. Activity of amino acid transport sy stems was determined by measuring the uptake of L-[H-3]leucine (L system) a nd L-[H-3]arginine (y(+)) under resting and shear stress condition. Shear s tress-mediated nitric oxide formation critically depended on the presence o f extracellular L-arginine, which increased shear stress-induced cGMP incre ases in a concentration dependent manner (EC50=123 mu M) In addition, shear stress increased L-arginine uptake, while the transport capacity for neutr al amino acids (L system) remained unchanged under shear stress conditions. Analysis of the kinetics of the uptake of L-arginine under resting and she ar stress conditions indicate that shear stress increased velocity of the h igh affinity, low capacity transport (y(+)) without affecting affinity of t his system. These data suggest that shear stress selectively activates upta ke of L-arginine in endothelial cells and that the uptake of L-arginine mig ht be important for shear stress-mediated nitric oxide formation.