FIG. 5.
Inhibition of monocyte ciprofloxacin transport by adenine. (A) Effect of nucleobases and nucleosides on transport. Monocytes were incubated with 5 μg of ciprofloxacin per ml and 5 mM indicated compound. Transport was monitored as previously described. The data are expressed as the mean and standard error of the mean of three experiments, with the asterisk denoting a significant difference from the control (P < 0.05, Dunnett's test). (B) Mechanism of inhibition of ciprofloxacin transport by adenine. Ciprofloxacin transport was assayed for 4 min in the presence and absence of 4 mM adenine. The mechanism of inhibition was competitive, with an observed Ki of 3.8 ± 1.1 mM. V, transport velocity in nanograms per minute per 106 cells. The data are means with standard errors of the means for four experiments.