L-ARGININE TRANSPORT IS INCREASED IN MACROPHAGES GENERATING NITRIC-OXIDE

Transport of L-arginine and nitrite production were examined in the murine macrophage cell line J774. Bacterial lipopolysaccharide (LPS) induced a dose- and time-dependent stimulation of nitrite production, which was further increased in the presence of interferon-gamma. Nitrite synthesis was absolutely dependent on extracellular L-arginine and inhibited in the presence of L-lysine or L-ornithine. In unactivated J774 cells L-arginine transport was saturable, with an apparent K(m) of 0.14 +/- 0.04 mM and V(max). of 15 +/- 2 nmol/h per 10(6) cells. LPS (1-mu-g/ml) induced a time-dependent stimulation of L-arginine transport, and after 24 h the V(max). increased to 34 +/- 2 nmol/h per 10(6) cells. These findings indicate that activation of J774 cells with LPS produces an increase in both L-arginine transport and nitrite synthesis. The elevated rate of L-arginine transport in activated J774 cells may provide a mechanism for sustained substrate supply during enhanced utilization of L-arginine for the generation of NO.