Ionic-diffusion Potential-dependent Transport of a New Quinolone, Sparfloxacin, Across Rat Intestinal Brush-border Membrane

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Abstract
The mechanism of uptake of sparfloxacin, a new quinolone, by intestinal brush‐border membrane vesicles was investigated to clarify whether there is a common transport process for new quinolones mediated by the diffusion potential across the intestinal membrane bilayer. Sparfloxacin was taken up pH‐dependently by rat intestinal brush‐border membrane vesicles, behaviour analogous to that of organic cations including enoxacin and ciprofloxacin. Transient overshooting uptake of this quinolone was observed in the presence of an outward H+ gradient. Momentary dissipation of the H+ gradient by addition of carbonyl cyanide p‐(trifluoromethoxy)phenylhydrazone did not affect the uptake of sparfloxacin, and a marked but incomplete reduction in the H+‐sensitive overshooting uptake of sparfloxacin was apparent in the voltage‐clamped brush‐border membrane vesicles. Furthermore, a valinomycin‐induced K+‐diffusion potential (interior negative) and an inward Cl—‐diffusion potential stimulated the initial uptake of Sparfloxacin at pH 5.5. Sparfloxacin uptake was inhibited by tetracaine and imipramine. The inhibitory effect of these cations correlated well with changes in membrane surface charges induced by the presence of tetracaine or imipramine. These results indicate that sparfloxacin transport across the brush‐border membrane depends upon the inside‐negative ionic diffusion potential, that the H+‐ or K+‐diffusion‐potential‐dependent uptake of sparfloxacin by intestinal brush‐border membrane vesicles is affected by the membrane surface potential and that inhibition of sparfloxacin uptake originates from changes in the membrane surface potential caused by the organic cations.

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