Characteristics of Uptake of Cefroxadine by Rabbit Small Intestinal Brush Border Membrane Vesicles

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Characteristics of transport of an oral aminocephalosporin, cefroxadine, in rabbit small intestinal brush border membrane vesicles were examined. Uptake rate of cefroxadine was saturable in the presence of an inward H^+ gradient, and kinetic parameters were similar to those of cephradine. However, the uptake rate was almost linear with the concentration in the absence of an inward H^+ gradient up to 5mM. Overshoot phenomenon was observed in the presence of an inward H^+ gradient at 37℃, but it disappeared with decrease of temperature. The Arrhenius plot of uptake rate constant showed a break point at approximately 30℃. Cefroxadine uptake was optimum in the vicinity of pH 5.5 at 37℃, but the dependence on extravesicular pH disappeared at 15℃. The uptake of cefroxadine in the presence of an inward H^+ gradient was markedly inhibited by other aminocephalosporins such as cephalexin, but the inhibition was only slight in the absence of an inward H^+ gradient. Alkyl alcohols such as n-hexyl alcohol also inhibited H^+-coupled uptake of cefroxadine at the concentration range at which the alcohols increased the membrane fluidity, and overshoot phenomenon diminished, suggesting that H^+-coupled transport of cefroxadine is sensitive to the alcohol-induced increase in membrane fluidity. On the other hand, the alcohols rather stimulated its uptake in the absence of an H^+ gradient.
公益社団法人日本薬学会の論文
1996-02-15