Abstract
BACKGROUND: Fluoroquinolones and tetracyclines can penetrate epithelial cells, but the mechanism by which they cross the plasma membrane is unclear. In this study, a cell line derived from oral epithelium was used as a model to demonstrate a role for active transport. METHODS: Transport of ciprofloxacin and minocycline by confluent cell monolayers was assayed by measuring the increase in cell-associated fluorescence. RESULTS: Uptake of both agents was saturable and was inhibited at low temperatures. At 37 degrees C, the cells transported ciprofloxacin and minocycline with Km values of 351 and 133 microg/ml, respectively, and maximum velocities of 5.11 and 13.4 ng/min/microg cell protein, respectively. When ciprofloxacin and minocycline were removed from the extracellular medium, the intracellular levels of both agents decreased. Ciprofloxacin efflux from loaded cells occurred more rapidly than with minocycline. Cells accumulated intracellular drug levels that were at least 8-fold higher than extracellular levels for ciprofloxacin and at least 40-fold higher for minocycline. Transport of ciprofloxacin and minocycline was significantly influenced by pH and was most favorable at pH 7.7 and 7.2, respectively. While ciprofloxacin transport was Na+ independent, minocycline transport was strongly inhibited when sodium in the medium was replaced with choline. Transport of both agents was inhibited by a variety of organic cations, but the pattern of inhibition was different. Papaverine, phenylephrine, and doxycycline competitively inhibited minocycline transport, but inhibited ciprofloxacin transport by a non-competitive mechanism. CONCLUSIONS: Epithelial cells take up ciprofloxacin and minocycline via different active transport systems. These transporters may play an important role in enhancing the effectiveness of these agents against invasive pathogens.