Structural Specificities for the Active Transport System of Thiamine in Rat Small Intestine

Komai, Toru; Shindo, Hideyo

doi:10.3177/jnsv.20.179

Cited by 22 publications

(12 citation statements)

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“…The competitive inhibition of thiamine analogues on the transport of thiamine has been reported in various biological systems (6,7,11,18,21). The present observation that hepatic thiamine uptake was significantly reduced in the presence of pyrithiamine, and, to a lesser degree, in the presence of oxythiamine (Table 1) was in complete agreement with previous reports.…”

Section: Discussionsupporting

confidence: 82%

“…Similar results were also obtained in other preparations (4,11,18). The nature of the transport system is similar to that demonstrated in the small intestine (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14), central nervous system (15)(16)(17)(18) and microorganisms (20)(21)(22)(23). The transport system for thiamine requires the presence of oxygen and is sodium dependent.…”

Section: Discussionmentioning

confidence: 61%

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Active transport of thiamine by freshly isolated rat hepatocytes.

Chen

1978

Journal of Nutritional Science and Vitaminology, J Nutr Sci Vit

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SummaryRat hepatocytes were freshly prepared from adult animals using the collagenase-perfusion technique. The hepatic transport of thiamine was studied in isolated liver cells. The process was found to be saturable with an apparent Kt of 0.31mM and a Vmax of 0.7 umoles/ml intracellular fluid/5 minutes. However, at higher substrate concentrations, the process proceeded in a linear fashion. Both pyrithiamine and oxythiamine were inhibitory on the hepatic uptake of thiamine, the latter showed much weaker activity than the former. The system required the presence of sodium ions and was sensitive to ouabain. Anaerobic condition and metabolic inhibitors, e.g., 2,4-dinitrophenol, cyanide, and iodoacetate suppressed the uptake rate of thiamine. Addition of ethanol in the incubation medium also caused significant reduction of thiamine uptake. Efflux studies indicated that a portion of intracellular thiamine is readily available for exodus. Chromatographic analyses showed that thiamine was only slightly metabolically altered during the transport process. It is suggested that thiamine is transported into isolated hepatic cells by an active, sodium-dependent process.

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Section: Discussionsupporting

confidence: 82%

Section: Discussionmentioning

confidence: 61%

Active transport of thiamine by freshly isolated rat hepatocytes.

Chen

1978

Journal of Nutritional Science and Vitaminology, J Nutr Sci Vit

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“…Another feature of the erythrocyte transport of thiamin, which dissociates as a monovalent cation at pH 7.4 (Komai & Shindo, 1974b), is that the uptake is not affected by a relatively negative intracellular space (Fig. 9), suggesting that transport is most probably an electroneutral process.…”

Section: Discussionmentioning

confidence: 99%

Thiamin transport by human erythrocytes and ghosts

et al. 1990

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Thiamin transport in human erythrocytes and resealed pink ghosts was evaluated by incubating both preparations at 37 or 20 degrees C in the presence of [3H]-thiamin of high specific activity. The rate of uptake was consistently higher in erythrocytes than in ghosts. In both preparations, the time course of uptake was independent from the presence of Na+ and did not reach equilibrium after 60 min incubation. At concentrations below 0.5 microM and at 37 degrees C, thiamin was taken up predominantly by a saturable mechanism in both erythrocytes and ghosts. Apparent kinetic constants were: for erythrocytes, Km = 0.12, 0.11 and 0.10 microM and Jmax = 0.01, 0.02 and 0.03 pmol.microliter-1 intracellular water after 3, 15, and 30 min incubation times, respectively; for ghosts, Km = 0.16 and 0.51 microM and Jmax = 0.01 and 0.04 pmol.microliter-1 intracellular water after 15 and 30 min incubation times, respectively. At 20 degrees C, the saturable component disappeared in both preparations. Erythrocyte thiamin transport was not influenced by the presence of D-glucose or metabolic inhibitors. In both preparations, thiamin transport was inhibited competitively by unlabeled thiamin, pyrithiamin, amprolium and, to a lesser extent, oxythiamin, the inhibiting effect being always more marked in erythrocytes than in ghosts. Only approximately 20% of the thiamin taken up by erythrocytes was protein- (probably membrane-) bound. A similar proportion was esterified to thiamin pyrophosphate. Separate experiments using valinomycin and SCN- showed that the transport of thiamin, which is a cation at pH 7.4, is unaffected by changes in membrane potential in both preparations.

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“…Thiamine is a physiologically charged monovalent cation that requires BBB carrier-mediated transport (2,4,5) to supply concentrations necessary for physiologic glucose utilization in neuron and glia (6,7). Similarly, choline transport at the BBB has been demonstrated (3,(8)(9)(10) to be carrier-mediated and saturable.…”

Section: Introductionmentioning

confidence: 97%