Purpose: Elucidating the transport characteristics of S-1090, a new orally active cephalosporin in rat small intestinal brush-border membranes.
Methods: A rapid filtration technique.
Results: The uptake of S-1090 was stimulated by an inwardly directed H(+)-gradient, but did not show overshooting uptake. To investigate the transport system, the inhibitory and countertransport effects of various compounds on S-1090 uptake were examined. Although the dipeptides and tripeptides composed of amino acids with aliphatic side chains did not inhibit the uptake of S-1090, those having histidine, proline or tryptophan as the N-terminal amino acid showed an inhibitory effect. Among the oral cephems tested, ceftibuten showed marked inhibition, while cefaclor and cephalexin had no inhibitory effect. Countertransport effects on S-1090 uptake were observed only when the vesicles were preloaded with histidyl peptides such as His-Gly or His-Ala, while other compounds which exhibited inhibition had no countertransport effect.
Conclusions: Based on the above results, there seems to be heterogeneity (multiplicity) in the oligopeptide transport system which may depend on the structure of the N-terminal amino acid. S-1090 may be dominantly transported via a system that recognizes peptides having histidine as the N-terminal amino acid.