Antibiotic translocation through membrane channels: temperature-dependent ion current fluctuation for catching the fast events.

Temperature-dependent facilitated permeation of antibiotics through membrane channels was investigated. Here we reconstituted single OmpF trimers from the outer membrane of Escherichia coli (E. coli) into a planar lipid bilayer. The penetration of ampicillin through OmpF causes fluctuation in the ion current, and analysis of the fluctuations at different temperatures allows us to determine the mode of permeation. The residence time of the drug inside the channel decays strongly with temperature, reaching the resolution limit of the instrument at 30 degrees C. The number of events increases exponentially with temperature up to 30 degrees C and then gradually decreases as temperature increases. At room temperature, we observe about 25 events per second per monomer of the trimeric channel and an extrapolation to 37 degrees C gives roughly 50 events. The activation energy for ampicillin translocation through OmpF is estimated to be around 13 kT. Temperature-dependent study gives new insights into the faster translocation of small substrates through biological nanopores.