Ethanol stimulates leucine uptake by rat fetal hepatocytes via trans-stimulation.
Prior studies showed that exposure of cultured rat fetal hepatocytes to ethanol increased sodium-independent transport of alpha-amino-isobutyric acid and cycloleucine. Using leucine (Leu) as a probe, we now show that this is a reflection of trans-stimulation of system L inward flux. Transport of Leu was entirely sodium independent and beta-2-aminobicyclo(2,2,1)-heptane-2-carboxylic acid inhibitable. Uptake kinetics indicated two components, likely systems L1 and L2 reported for the adult hepatocyte. The low-affinity Km was in the 0.5 mM range, whereas the high-affinity Km was 2% of that value. Under optimal growth conditions, approximately 65% of the Leu was transported by the latter system. Strong bidirectional exchange was shown with Leu loading, stimulating initial Leu uptake by 66%. Externally directed transport was enhanced 2.9 times against 5 x 10(-3) M Leu vs. no external Leu. A 24-h exposure to ethanol (2 mg/ml) increased Leu uptake by up to 100%, an effect that could be mimicked by arrested cell replication. Both enhanced rates could be reversed by amino acid depletion, reflecting intracellular amino accrual that induced trans-stimulation of Leu uptake. Enhanced uptake was also reproduced in replicating cells by loading with increasing concentrations of Leu.
Henderson
G I
GI
Department of Medicine, University of Texas Health Science Center, San Antonio 78284.
Frosto
T A
TA
Heitman
D W
DW
Schenker
S
S
D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002478:Cells, Cultured; D000431:Ethanol / Q000494:pharmacology*; D005333:Fetus; D007700:Kinetics; D007930:Leucine / Q000378:metabolism*; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000494:pharmacology
D000431:Ethanol; D012964:Sodium; D007930:Leucine