Thiamine transport by basolateral rat liver plasma membrane vesicles.
Hepatic thiamine transport is thought to be a saturable, Na(+)- and energy-dependent process. However, the transport of this organic cation has not been examined in experimental models that allow direct characterization of carrier-mediated processes. Recently, a sinusoidal organic cation/H+ antiport was identified, using N1-methylnicotinamide as a marker. To determine whether thiamine is a substrate for this antiport, the characteristics of thiamine uptake were examined in rat liver basolateral membrane vesicles. An inwardly directed Na+ gradient had no effect on thiamine uptake as compared with an identical K+ gradient. An outwardly directed H+ gradient stimulated thiamine uptake as compared with pH-equilibrated conditions, and H(+)-dependent uptake was not the result of an H+ diffusion potential. Identical pH gradients stimulated uptake under voltage-clamped conditions, consistent with electroneutral thiamine/H+ exchange. Unlabeled intravesicular thiamine trans-stimulated [3H]thiamine uptake. Choline and imipramine cis-inhibited thiamine/H+ exchange; a series of other organic cations and thiamine analogues had no effect. Carrier-mediated [3H]thiamine uptake showed two saturable systems. In conclusion, a thiamine/H+ antiport is present on the sinusoidal membrane, distinct from Na+/H+ and NMN+/H+ exchange.
Moseley
R H
RH
Department of Internal Medicine, Veterans Affairs Medical Center, Ann Arbor, Michigan.
Vashi
P G
PG
Jarose
S M
SM
Dickinson
C J
CJ
Permoad
P A
PA
D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone / Q000494:pharmacology; D002462:Cell Membrane / Q000378:metabolism; D006859:Hydrogen / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D008099:Liver / Q000378:metabolism* / Q000648:ultrastructure; D009994:Osmolar Concentration; D011188:Potassium / Q000378:metabolism; D051381:Rats; D012964:Sodium / Q000378:metabolism; D013831:Thiamine / Q000493:pharmacokinetics*; D014634:Valinomycin / Q000494:pharmacology
D014634:Valinomycin; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; D006859:Hydrogen; D012964:Sodium; D011188:Potassium; D013831:Thiamine