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

The transport characteristics of ceftibuten, a dianionic cephem antibi otic, in rat renal and intestinal brush-border membranes were compared . Ceftibuten transport was mediated by two transport systems in the re nal brush-border membrane and by one transport system in the intestina l brush-border membrane. The apparent kinetic parameters for the uptak e of ceftibuten by the renal brush-border membrane vesicles, respectiv ely, were: K-m1, K-m2 values of 26 and 1946 mu M and V-max1, V-max2 va lues of 105 and 1400 pmol/mg protein per 30 s. The apparent kinetic pa rameters for the uptake by the intestinal brush-border membrane vesicl es were: K-m of 425 mu M and V-max of 1701 pmol/mg protein per 30 s. I n the renal brush-border membrane, L-Ala-L-Pro was partially competiti ve and competitive inhibitor for the uptake by the high and low affini ty systems, respectively. However, L-Ala-L-Pro was a non-competitive i nhibitor for the uptake by the intestinal brush-border membrane vesicl es. L-Carnosine was a specific and competitive inhibitor for the high affinity system in the renal brush-border membrane, while it had no ef fect on the low affinity system of the kidney or on the transport syst em of the intestine. It was concluded that the transport characteristi cs of ceftibuten in the renal and intestinal brush-border membranes ar e similar in some aspects but they are not identical.