PT  - JOURNAL ARTICLE
AU  - Tsuji, A
AU  - Terasaki, T
AU  - Tamai, I
AU  - Hirooka, H
TI  - H+ gradient-dependent and carrier-mediated transport of cefixime, a new cephalosporin antibiotic, across brush-border membrane vesicles from rat small intestine.
DP  - 1987 May 01
TA  - Journal of Pharmacology and Experimental Therapeutics
PG  - 594--601
VI  - 241
IP  - 2
4099  - http://jpet.aspetjournals.org/content/241/2/594.short
4100  - http://jpet.aspetjournals.org/content/241/2/594.full
SO  - J Pharmacol Exp Ther1987 May 01; 241
AB  - The characteristics of the transport of cefixime, a new p.o. cephalosporin, antibiotic, were studied by using brush-border membrane vesicles from the rat small intestine. The initial rate of uptake of cefixime was not affected by the presence of an inward gradient of either Na+ or other monovalent cations. With an intravesicular pHi of 7.5, optimal cefixime uptake occurred at an extravesicular pHo of 5.0, with about 6-fold acceleration compared with that in the absence of an inward proton gradient (pHi = pHo = 7.5). A protonophore, carbonyl-cyanide-4-trifluoromethoxy-phenylhydrazone, abolished the stimulating effect of low pHo. In the presence of a sufficient inward proton gradient (pHi = 7.5, pHo = 5.0), cefixime uptake showed an overshoot phenomenon and apparent saturation kinetics expressed by the Michaelis-Menten equation with the maximum rate of 2.67 +/- 0.06 nmol/30 sec/mg of protein and a Michaelis constant of 0.83 +/- 0.04 mM. Cefixime uptake was inhibited competitively by glycyl-L-proline and stimulated by the countertransport effect of this dipeptide. The other peptides also inhibited cefixime uptake significantly. A valinomycin-induced inside-negative K+-diffusion potential had a dramatic reducing effect on the uptake of dianionic cefixime. All the data obtained in this study demonstrate that cefixime transport across the brush-border membrane vesicles is carrier-mediated, independent of Na+ and dependent on a H+ gradient via the peptide transport systems.