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 transport mechanisms and the role of extracellular L-arginine in nitric oxide formation during shear stress activation of endothelial cells. Porcine aortic endothelial cells were grown to confluence and were exposed to various amounts of shear stress for 40 min. Formation of nitric oxide was monitored by measuring elevation of endothelial cGMP. Activity of amino acid transport systems was determined by measuring the uptake of L-[3H]leucine (L system) and L-[3H]arginine (y+) under resting and shear stress condition. Shear stress-mediated nitric oxide formation critically depended on the presence of extracellular L-arginine, which increased shear stress-induced cGMP increases in a concentration dependent manner (EC50=123 microM). In addition, shear stress increased L-arginine uptake, while the transport capacity for neutral amino acids (L system) remained unchanged under shear stress conditions. Analysis of the kinetics of the uptake of L-arginine under resting and shear stress conditions indicate that shear stress increased velocity of the high affinity, low capacity transport (y+) without affecting affinity of this system. These data suggest that shear stress selectively activates uptake of L-arginine in endothelial cells and that the uptake of L-arginine might be important for shear stress-mediated nitric oxide formation.