| Autor: |
Moseley, Richard H., Vashi, Pankaj G., Jarose, Suzanne M., Dickinson, Chris J., Permoad, Patricia A. |
| Zdroj: |
Gastroenterology; September 1992, Vol. 103 Issue: 3 p1056-1065, 10p |
| Abstrakt: |
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. |
| Databáze: |
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