Representative sections of current traces of a single OmpF porin recorded at −100 mV (A–D) and +100 mV (E–H) measured in an asymmetrical LPS membrane. Traces were obtained without antibiotic (A and E), with 0.1 mM (B and F) and 0.3 mM enrofloxacin (C and G) on the trans side and 0.3 mM enrofloxacin on the cis side (D and H). The level of full current (all three pores open) is not affected in the presence of enrofloxacin at negative potentials (B–D), regardless of whether it is applied at the trans (B and C) or cis (D) side. At +100 mV, enrofloxacin causes apparent current reduction and a strong increase in noise which is smaller when given at the cis side (H) than at the trans side (F and G). Enrofloxacin given at the cis side at −100 mV causes pronounced slow blocking events (D). All measurements of this and the following graphs were performed at 37°C.