Thiamin uptake by rat isolated enterocytes: Relationship between transport and phosphorylation

Abstract

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 μM rotenone and a short (30 s) incubation time, while the intracellular metabolic step was assessed by using nor-moenergized (normal) cells incubated for a longer (30 min) time. Evaluation of K_m, J_max and K_D (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 K_m and J_max values of the saturable components in nor-moenergized 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.

Key Words:

• thiamin uptake
• isolated enterocytes
• transport kinetics
• tandem process