COMPARISON OF THE TRANSPORT CHARACTERISTICS OF CEFTIBUTEN IN RAT RENAL AND INTESTINAL BRUSH-BORDER MEMBRANES

The transport characteristics of ceftibuten, a dianionic cephem antibiotic, in rat renal and intestinal brush-border membranes were compared. Ceftibuten transport was mediated by two transport systems in the renal brush-border membrane and by one transport system in the intestinal brush-border membrane. The apparent kinetic parameters for the uptake of ceftibuten by the renal brush-border membrane vesicles, respectively, were: K-m1, K-m2 values of 26 and 1946 mu M and V-max1, V-max2 values of 105 and 1400 pmol/mg protein per 30 s. The apparent kinetic parameters for the uptake by the intestinal brush-border membrane vesicles were: K-m of 425 mu M and V-max of 1701 pmol/mg protein per 30 s. In the renal brush-border membrane, L-Ala-L-Pro was partially competitive and competitive inhibitor for the uptake by the high and low affinity systems, respectively. However, L-Ala-L-Pro was a non-competitive inhibitor for the uptake by the intestinal brush-border membrane vesicles. L-Carnosine was a specific and competitive inhibitor for the high affinity system in the renal brush-border membrane, while it had no effect on the low affinity system of the kidney or on the transport system of the intestine. It was concluded that the transport characteristics of ceftibuten in the renal and intestinal brush-border membranes are similar in some aspects but they are not identical.