title: Excess white noise to probe transport mechanisms in a membrane channel.
abstract: Current fluctuation analysis has been successfully used over the years to investigate the physical properties of different systems. Here, we perform single-channel time-resolved current experiments in a protein channel to evaluate the different transport mechanisms governing the channel function. Using different salts of monovalent and divalent cations in a wide range of concentrations and applied potentials, we analyze current fluctuations focusing on the voltage dependence of the additional white noise that appears in the low-frequency range of the spectra. We demonstrate that the channel displays two characteristic transport regimes: at low salt concentrations (10 mM to 1 M) ion permeation is controlled by the protein fixed charges that induce accumulation or exclusion of ions to preserve local electroneutrality. At high salt concentrations (>1M) adsorption processes associated to the binding of cations to the channel charges regulate the transport properties.
authors.affiliation: Laboratory of Molecular Biophysics, Department of Physics, Universitat Jaume I, 12071 Castellón, Spain.
authors.forename: María
authors.initials: M
authors.lastname: Queralt-Martín
authors.affiliation: Laboratory of Molecular Biophysics, Department of Physics, Universitat Jaume I, 12071 Castellón, Spain.
authors.forename: M
authors.initials: M
authors.lastname: Lidón López
authors.affiliation: Laboratory of Molecular Biophysics, Department of Physics, Universitat Jaume I, 12071 Castellón, Spain.
authors.forename: Antonio
authors.initials: A
authors.lastname: Alcaraz
mesh_terms: D001692:Biological Transport / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004573:Electrolytes / Q000494:pharmacology; D015640:Ion Channel Gating / Q000187:drug effects; D008954:Models, Biological; D018272:Porins / Q000378:metabolism*
chemical_list: D004573:Electrolytes; C109237:OmpF protein; D018272:Porins