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Binding and transport of methotrexate and its derivative, MX‐68, across the brush‐border membrane in rat kidney
Author(s) -
Han YongHae,
Kato Yukio,
Sugiyama Yuichi
Publication year - 1999
Publication title -
biopharmaceutics and drug disposition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.419
H-Index - 58
eISSN - 1099-081X
pISSN - 0142-2782
DOI - 10.1002/1099-081x(199911)20:8<361::aid-bdd202>3.0.co;2-o
Subject(s) - brush border , osmotic concentration , chemistry , reabsorption , cotransporter , biochemistry , folic acid , biophysics , membrane , vesicle , sodium , biology , medicine , organic chemistry
Binding and transport properties of methotrexate (MTX) and its novel derivative, MX‐68, were examined in brush‐border membrane vesicles (BBMVs) isolated from rat kidneys. The uptake of MTX, MX‐68 and folic acid by BBMVs was stimulated by an inwardly‐directed H + gradient. Such H + ‐dependent uptake of folic acid is compatible with a previous report (Bhandari et al. , Biochim Biophys Acta 1988; 937: 211). The MTX uptake exhibits saturation with a K m of 0.834 µM. Although the uptake of these three compounds at optimal pH depended on the osmolarity of the medium, a substantial portion of the uptake was osmolarity‐insensitive. By changing the medium osmolarity, the uptake by BBMVs could be separately discriminated as osmolarity‐sensitive and insensitive portions, representing transport into the intravesicular space and binding to the surface of BBMVs, respectively. For all three compounds, the binding increased in a time‐dependent manner, while the amount transported reached a maximum after a relatively short incubation period. The transport of folic acid, but not its binding, exhibited an overshoot phenomenon under conditions of an inward H + gradient. The present results suggest that reabsorption of MTX and MX‐68 in the kidney is governed by both their binding and transport mechanisms, with a similar kinetic profile to that of folic acid. The involvement of a transport system seems to make a relatively small contribution to the reabsorption of MTX assessed in BBMVs compared with MX‐68 and folic acid. Copyright © 1999 John Wiley & Sons, Ltd.