Thiamin uptake by rat isolated enterocytes: relationship between transport and phosphorylation.

The membrane and intracellular steps of thiamin (T) uptake were studied in rat isolated enterocytes. The membrane step was investigated by using enterocytes deenergized with 25 microM rotenone and a short (30 s) incubation time, while the intracellular metabolic step was assessed by using normoenergized (normal) cells incubated for a longer (30 min) time. Evaluation of Km, Jmax and KD (apparent passive permeability coefficient) values, at 30 s incubation, indicated that deenergization slightly reduced both the affinity and the capacity of the saturable component of T uptake, as well as the capacity of the non-saturable component. At 30 min incubation, deenergization suppressed completely the saturable component, without affecting the non-saturable component. Comparison of the Km and Jmax values of the saturable components in normoenergized enterocytes at 30 s and 30 min indicated that intracellular metabolic phosphorylation is probably the event responsible for the active process involved in T uptake.