Transport mechanisms of nucleosides and the derivative, 6-mercaptopurine riboside across rat intestinal brush-border membranes

Na +-driven nucleoside transport processes across rat intestinal brush-border membrane vesicles were investigated. 6-Mercaptopurine riboside (6-MPR), an analogue of purine-nucleoside such as adenosine and inosine, was recognized by its purine- and pyrimidine-nucleosides transport system, but their n...

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Bibliographic Details
Published in:	Biochimica et biophysica acta. Biomembranes Vol. 1278; no. 1; pp. 105 - 110
Main Authors:	Iseki, Ken, Sugawara, Mitsuru, Fujiwara, Toshie, Naasani, Imad, Kobayashi, Michiya, Miyazaki, Katsumi
Format:	Journal Article
Language:	English
Published:	Elsevier B.V 01-01-1996
Subjects:	6-Mercaptopurine riboside Brush-border membrane Nucleoside transport Rat Small intestine Sodium ion dependence Mes, 2-( N-morpholino)ethanesulfonic acid Sodium ion dependence Rat Brush-border membrane Hepes, N-2-hydroxyethylpiperazine- N′-2-ethane-sulfonic acid 6-MPR Nucleoside transport Small intestine 6-Mercaptopurine riboside
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Summary:	Na +-driven nucleoside transport processes across rat intestinal brush-border membrane vesicles were investigated. 6-Mercaptopurine riboside (6-MPR), an analogue of purine-nucleoside such as adenosine and inosine, was recognized by its purine- and pyrimidine-nucleosides transport system, but their nucleo-bases did not entirely inhibit the 6-MPR transport. The analysis according to the Hill equation of the curve for Na + activation of 6-MPR uptake was consistent with the notion of a Na +/6-MPR coupling stoichiometry of 1:1. The expressed transport activities of adenosine, uridine, and 6-MPR were Na +-dependent and saturable, and their affinity constants ( K mvalue) obtained by Eadie-Hofstee analysis were approx. 20, 15 and 100 μM. Moreover, the uptake of radiolabeled adenosine and uridine was trans-stimulated by 6-MPR inside vesicles in the absence of an inwardly directed Na +-gradient. On the other hand, uridine did not exhibit any inhibitory effects on the uptake of adenosine despite the fact that adenosine was a potent inhibitor for uridine uptake by intestinal brush-border membrane vesicles. These differences in the inhibition may be explained by the multiplicity of the nucleoside transport systems.
ISSN:	0005-2736 1879-2642
DOI:	10.1016/0005-2736(95)00198-0