title: Transport and metabolism of thiamin in isolated rat hepatocytes.
abstract: This study examines thiamin transport in isolated rat hepatocytes and its relationship to thiamin phosphorylation. In an Na+ medium, [35S]thiamin, 3 microM, was accumulated rapidly by the cells, and a near study state intra-/extracellular distribution ratio of 3 was attained in 1 min. However, the uptake of radioactivity continued to increase with time owing principally to the accumulation of [35S]thiamin pyrophosphate (TPP). In a choline, Li+ or K+ medium, the steady state intra-/extracellular distribution ratio of [35S]thiamin was decreased to less than or equal to 1.1. Accordingly, the rate of formation of [35S]TPP also decreased. Ouabain and uncouplers of oxidative phosphorylation significantly lowered the distribution ratio of intra-/extracellular [35S]thiamin. These data indicate that thiamin transport in liver is concentrative, Na+-dependent, and dependent on biological energy. Additionally, they suggest that thiamin transport plays a significant role in governing the rate of synthesis of TPP. Neither pyrithiamin, an inhibitor of thiamin pyrophosphokinase nor o-benzoylthiamin disulfide, a permeable thiamin analog, affected the distribution ratio of intra-/extracellular [35S]thiamin, but preferentially inhibited the phosphorylation of [35S]thiamin. By contrast, amprolium primarily inhibited uptake. These data suggest that thiamin transport and phosphorylation can be differentiated by the action of appropriate inhibitors.
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002794:Choline / Q000494:pharmacology; D066298:In Vitro Techniques; D007700:Kinetics; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D011745:Pyrithiamine / Q000494:pharmacology; D051381:Rats; D012964:Sodium / Q000494:pharmacology; D013831:Thiamine / Q000031:analogs & derivatives / Q000378:metabolism* / Q000494:pharmacology; D013835:Thiamine Pyrophosphate / Q000378:metabolism; D014475:Uncoupling Agents / Q000494:pharmacology
chemical_list: D014475:Uncoupling Agents; D011745:Pyrithiamine; D012964:Sodium; D002794:Choline; D013835:Thiamine Pyrophosphate; D013831:Thiamine