H+ coupled transport of orally active cephalosporins lacking an α-amino group across brush-border membrane vesicles from rat small intestine

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Abstract
The effect of an inwardly directed H+ gradient on the transport characteristics of ceftibuten, cefixime and analogues of ceftibuten in rat intestinal brush-border membrane vesicles have been investigated. In the presence of a transmembrane H+ gradient, ceftibuten and its analogues exhibited a peak to equilibrium overshoot and an accumulation in the vesicles against the concentration gradient. However, the uptake of cefixime and S-1006 [(6R, 7R)-(7-[(Z)-2-(2-aminothiazol-4-yl)-2-pentenoylamino]-8-oxo-3-carba-moyloxy-methyl-5-thia-1-azabicyclo[4,2,0]oct-2-ene-2-carboxylic acid), which lacks a carboxyl group at position 4 of carboxyethylidene structure, exhibited no overshoot, although the equilibrium uptake was increased by a H+ gradient. The equilibrium uptake was dependent on the pH of the final incubation medium and the H + gradient. These data suggested that the orally active cephalosporins were transported into rat intestinal brush-border membrane by the transmembrane H+ gradient and the pH of the medium.

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