THE STIMULATIVE EFFECT OF DIFFUSION POTENTIAL ON ENOXACIN UPTAKE ACROSS RAT INTESTINAL BRUSH-BORDER MEMBRANES

Evidence of a membrane potential dependence for enoxacin uptake by rat intestinal brush-border membrane vesicles has been found. The transie nt overshooting uptake of enoxacin disappeared in the voltage-clamped brush-border membrane vesicles in the presence of an outward H+-gradie nt. Momentary dissipation of the H+-gradient itself by carbonyl cyanid e p-(trifluoromethoxy)phenylhydrazone (FCCP) did not affect the uptake of enoxacin. In contrast, enoxacin uptake was depressed by an interio r positive K+-diffusion potential induced by valinomycin. Furthermore, not only the outward H+-gradient but also an inward Cl--gradient caus ed a stimulating effect on enoxacin uptake, and the stimulation by the Cl--gradient was dissipated by using voltage-clamped membrane vesicle s. These results indicate that enoxacin transportation across the brus h-border membrane is dependent on the ionic diffusion potential. On th e other hand, neither Gly-Gly nor guanidine had any effect on enoxacin uptake by the membrane vesicles in the presence of an inward (for Gly -Gly) or outward (for guanidine) H+-gradient as a driving force for ea ch transport system. Therefore, it seems that enoxacin transport throu gh the intestinal epithelia does not participate in the carrier-mediat ed transport systems for Gly-Gly and guanidine.