Multiplicity of the H⁺-dependent transport mechanism of dipeptide and anionic β-lactam antibiotic ceftibuten in rat intestinal brush-border membrane

To elucidate the transport characteristics of the H⁺/dipeptide carrier that recognizes the orally active β-lactam antibiotic ceftibuten, the uptake behaviors were compared of ceftibuten and Gly-Sar by rat intestinal brush- border membrane vesicles. The results show that 1) both the uptake of ceftibuten and that of Gly-Sar were dependent on an inwardly directed H⁺ gradient; 2) anionic compounds such as hippurylphenyllactic acid competitively inhibited ceftibuten uptake in the presence of H⁺ gradient, whereas this anion did not inhibit Gly-Sar uptake; and 3) the carrier- mediated uptake of ceftibuten did not disappear even in the presence of 20 mM Gly-Sar. The results provide an evidence that several transporters with different features are potentially responsible for the uptake of β-lactam antibiotics into the intestinal cells. It is suggested that the dianionic β- lactam antibiotics that carry a net negative charge such as ceftibuten use multiple H⁺-dependent transport systems for absorption.