@article {Closs68, author = {Ellen I. Closs and Jan-Stefan Scheld and Masoumeh Sharafi and Ulrich F{\"o}rstermann}, title = {Substrate Supply for Nitric-Oxide Synthase in Macrophages and Endothelial Cells: Role of Cationic Amino Acid Transporters}, volume = {57}, number = {1}, pages = {68--74}, year = {2000}, publisher = {American Society for Pharmacology and Experimental Therapeutics}, abstract = {The current study was designed to investigate the importance of cationic amino acid transporters (CATs) for the l-arginine supply to nitric oxide (NO) synthases in mouse J774A.1 macrophages and human EA.hy926 endothelial cells. CAT-1 was expressed in both cell types, whereas CAT-2B was only expressed in activated macrophages. Apparent K M values for transport ofl-arginine in both cell types was consistent with the expression of the system y+ carriers CAT-1 (and CAT-2B in macrophages). In addition, l-arginine transport was Na+ independent and sensitive totrans-stimulation. A 2-h preincubation of activated macrophages in 2 mM l-lysine (which is exchanged forl-arginine by the CATs) reduced the intracellularl-arginine concentration from 2 mM to 160 μM. At the same time, nitric-oxide synthase (NOS) II activity was completely abolished. NOS II activity could be restored with extracellularl-arginine. No difference in NO production was seen between macrophages preincubated in l-arginine-containing buffer and incubated either with or without l-arginine during the 2-min NO assay. Incubation of endothelial cells in 2 mMl-lysine for up to 24 h decreased the intracellular l-arginine concentration from 3.5 mM to about 600 μM but did not reduce the NOS III activity. Our results suggest that both activated macrophages and endothelial cells have anl-arginine pool that is not freely exchangeable with the extracellular space. This pool seems to be accessible to NOS III in endothelial cells but not to NOS II in macrophages. The American Society for Pharmacology and Experimental Therapeutics}, issn = {0026-895X}, URL = {https://molpharm.aspetjournals.org/content/57/1/68}, eprint = {https://molpharm.aspetjournals.org/content/57/1/68.full.pdf}, journal = {Molecular Pharmacology} }