Role of L-citrulline transport in nitric oxide synthesis in rat aortic smooth muscle cells activated with LPS and interferon-gamma.
(1) l-citrulline, a coproduct of nitric oxide synthase (NOS)-catalysed metabolism of l-arginine to nitric oxide (NO), is an important intermediate of the urea cycle and a precursor for l-arginine biosynthesis in vascular cells. (2) In the present study, we have examined the characteristics of l-citrulline transport, regulation by lipopolysaccharide (LPS) and interferon-gamma (IFN-gamma) and the ability of l-citrulline to sustain NO synthesis in rat cultured aortic smooth muscle cells. (3) l-citrulline transport was saturable with an apparent Km=1.6+/-0.2 mm and Vmax=5.9+/-0.6 pmol microg-1 protein min-1. Transport was pH-insensitive, partially Na+-dependent and markedly inhibited by substrates selective for amino-acid transport systems L and N but not by l-arginine or substrates for systems A, ASC, xc- or XAG. Moreover, transport was not altered in cells treated with LPS (100 microg ml-1) and IFN-gamma (50 U ml-1) for 0-24 h. (4) Unlike l-arginine, l-citrulline could not sustain maximal NO production in cells expressing iNOS. (5) Our findings provide the first evidence in vascular smooth muscle cells that l-citrulline transport is mediated via a low-affinity carrier with characteristics resembling systems L and N. Moreover, in l-arginine-deprived rat aortic smooth muscle cells, l-citrulline cannot sustain maximal NO release via iNOS.
Wileman
Samantha M
SM
Centre for Cardiovascular Biology & Medicine, GKT School of Biomedical Sciences, King's College London, Guy's Campus, London SE1 1UL.
Mann
Giovanni E
GE
Pearson
Jeremy D
JD
Baydoun
Anwar R
AR
D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects / Q000378:metabolism*; D001692:Biological Transport / Q000502:physiology; D002478:Cells, Cultured; D002956:Citrulline / Q000493:pharmacokinetics*; D004305:Dose-Response Relationship, Drug; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism*; D009569:Nitric Oxide / Q000096:biosynthesis*; D051381:Rats; D017207:Rats, Sprague-Dawley
D002956:Citrulline; D009569:Nitric Oxide