title: H+ gradient-dependent and carrier-mediated transport of cefixime, a new cephalosporin antibiotic, across brush-border membrane vesicles from rat small intestine.
abstract: 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.
mesh_terms: D000596:Amino Acids / Q000494:pharmacology; D000818:Animals; D001693:Biological Transport, Active; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone / Q000494:pharmacology; D020682:Cefixime; D002439:Cefotaxime / Q000031:analogs & derivatives* / Q000378:metabolism; D004151:Dipeptides / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007421:Intestine, Small / Q000378:metabolism / Q000648:ultrastructure*; D007700:Kinetics; D008297:Male; D008433:Mathematics; D008564:Membrane Potentials / Q000187:drug effects; D008871:Microvilli / Q000378:metabolism; D009842:Oligopeptides / Q000494:pharmacology; D009994:Osmolar Concentration; D051381:Rats; D011919:Rats, Inbred Strains; D013696:Temperature
chemical_list: D000596:Amino Acids; D004151:Dipeptides; D009842:Oligopeptides; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; C015248:glycylproline; D020682:Cefixime; D002439:Cefotaxime