Effects of ethanol on L-arginine transport in rat Ito cells in relation to nitric oxide production.
BACKGROUND
Nitric oxide (NO) is a potent mediator of hepatic sinusoidal hemodynamics that is synthesized in the hepatic stellate cells (Ito cells, fat-storing cells) and affects these cells. NO production may depend on the induction of inducible nitric oxide synthase and on transport of extracellular L-arginine. The precise mechanism that controls NO production in stellate cells was characterized recently.


METHODS
Kinetic analysis of L-arginine transport and reverse transcription-polymerase chain reaction for cationic amino acid transporter (CAT) were carried out by using stellate cells prepared from the male Wistar rat. The effect of ethanol on L-arginine transport and NO production of stellate cells was assessed in the presence of tumor necrosis factor (TNF)-alpha and interferon (IFN)-gamma.


RESULTS
The L-arginine transport system functioning in the hepatic stellate cells was system y+, possibly mediated by CAT-1 and CAT-2B (Km approximately 50 microM). IFN-gamma in combination with TNF-alpha induced NO production with an enhancement in CAT-2B mRNA expression and L-arginine transport, whereas L-arginine transport and NO production were suppressed by coincubated ethanol.


CONCLUSIONS
In hepatic stellate cells, ethanol has suppressive effects on NO production and extracellular L-arginine transport in the presence of TNF-alpha and IFN-gamma. The estimated Km of L-arginine transporter in hepatic stellate cells is very similar to the physiological L-arginine concentration in portal vein. Our findings may support the merit of further studies on the modulation of NO production via access to portal blood L-arginine concentration to control disturbed hepatic sinusoidal blood flow in patients with alcoholic liver disease.
Saibara
T
T
First Department of Medicine, Kochi Medical School, Nankoku 783, Japan. saibarat@kochi-ms.ac.jp
Ono
M
M
Iwasaki
S
S
Maeda
T
T
Onishi
S
S
Hayashi And
Y
Y
Enzan
H
H
D026923:Amino Acid Transport Systems, Basic; D000818:Animals; D001120:Arginine / Q000378:metabolism*; D001692:Biological Transport / Q000187:drug effects; D002352:Carrier Proteins / Q000235:genetics; D000431:Ethanol / Q000494:pharmacology*; D007371:Interferon-gamma / Q000494:pharmacology; D007700:Kinetics; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D008565:Membrane Proteins / Q000235:genetics; D009569:Nitric Oxide / Q000096:biosynthesis*; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017208:Rats, Wistar; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology
D026923:Amino Acid Transport Systems, Basic; D002352:Carrier Proteins; D008565:Membrane Proteins; D012333:RNA, Messenger; D014409:Tumor Necrosis Factor-alpha; D009569:Nitric Oxide; D000431:Ethanol; D007371:Interferon-gamma; D001120:Arginine