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Discrimination between citrulline and arginine transport in activated murine macrophages: inefficient synthesis of NO from recycling of citrulline to arginine
Author(s) -
Baydoun Anwar R.,
Bogle Richard G.,
Pearson Jeremy D.,
Mann Giovanni E.
Publication year - 1994
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1994.tb13099.x
Subject(s) - citrulline , arginine , nitric oxide , chemistry , extracellular , biochemistry , nitrite , amino acid , organic chemistry , nitrate
1 The kinetics, specificity, pH‐ and Na + ‐dependency of l ‐citrulline transport were examined in unstimulated and lipopolysaccharide (LPS)‐activated murine macrophage J774 cells. The dependency of nitric oxide production on extracellular arginine or citrulline was investigated in cells activated with LPS (1 μg ml −1 ) for 24 h. 2 In unstimulated J774 cells, transport of citrulline was saturable ( K t = 0.16 m m and V max = 32 pmol μg −1 protein min −1 ), pH‐insensitive and partially Na + ‐dependent. In contrast to arginine, transport of citrulline was unchanged in LPS‐activated (1 μg ml −1 , 24 h) cells. 3 Kinetic inhibition experiments revealed that arginine was a relatively poor inhibitor of citrulline transport, whilst citrulline was a more potent inhibitor ( K i = 3.4 m m ) of arginine transport but only in the presence of extracellular Na + . Neutral amino acids inhibited citrulline transport ( K i = 0.2–0.3 m m ), but were poor inhibitors of arginine transport. 4 Activated J774 cells did not release nitrite in the absence of exogenous arginine. Addition of citrulline (0.01 − 10 m m ), in the absence of exogenous arginine, could only partially restore the ability of cells to synthesize nitrite, which was abolished by 100 μ m N G ‐nitro‐ l ‐arginine methyl ester or N G ‐iminoethyl‐ l ‐ornithine. 5 Intracellular metabolism of l ‐[ 14 C]‐citrulline to l ‐[ 14 C]‐arginine was detected in unstimulated J774 cells and was increased further in cells activated with LPS and interferon‐γ. 6 We conclude that J774 macrophage cells transport citrulline via a saturable but nonselective neutral carrier which is insensitive to induction by LPS. In contrast, transport of arginine via the cationic amino acid system y + is induced in J774 cells activated with LPS. 7 Our findings also confirm that citrulline can be recycled to arginine in activated J774 macrophage cells. Although this pathway provides a mechanism for enhanced arginine generation required for NO production under conditions of limited arginine availability, it cannot sustain maximal rates of NO synthesis.