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  • Title: Exogenous NG-hydroxyl-L-arginine causes nitrite production in vascular smooth muscle cells in the absence of nitric oxide synthase activity.
    Author: Schott CA, Bogen CM, Vetrovsky P, Berton CC, Stoclet JC.
    Journal: FEBS Lett; 1994 Mar 21; 341(2-3):203-7. PubMed ID: 7511114.
    Abstract:
    Nitric oxide (NO) production from exogenous NG-hydroxy-L-arginine (OH-L-Arg) was investigated in rat aortic smooth muscle cells in culture by measuring nitrite accumulation in the culture medium. As well, the interaction between OH-L-Arg and L-arginine uptake via the y+ cationic amino acid transporter was studied. In cells without NO-synthase activity, OH-L-Arg (1-1000 microM) induced a dose-dependent nitrite production with a half-maximal effective concentration (EC50) of 18.0 +/- 1.5 microM (n = 4-7). This nitrite accumulation was not inhibited by the NO-synthase inhibitor NG-nitro-L-arginine methyl ester, L-NAME (300 microM). In contrast, it was abolished by miconazole (100 microM), an inhibitor of cytochrome P450. Incubation of vascular smooth muscle cells with LPS (10 micrograms/ml) induced an L-NAME inhibited nitrite accumulation, but did not enhance the OH-L-Arg induced nitrite production. OH-L-Arg and other cationic amino acids, L-lysine and L-ornithine, competitively inhibited [3H]-L-arginine uptake in rat aortic smooth muscle cells, with inhibition constants of 195 +/- 23 microM (n = 12), 260 +/- 40 microM (n = 5) and 330 +/- 10 microM (n = 5), respectively. These results show that OH-L-Arg is recognized by the cationic L-amino acid carrier present in vascular smooth muscle cells can be oxidized to NO and nitrite in these cells in the absence of NO-synthase, probably by cytochrome P450 or by a reaction involving a cytochrome P450 by-product.
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