Linearity, saturation and blocking in a large multiionic channel: Divalent cation modulation of the OmpF porin conductance

► Divalent cations in the OmpF channel give rise to effects not found in salts of monovalent cations. ► Discrimination of the different roles of the electrolyte and the protein channel. ► Current saturation and blocking may also be observed in large channels. ► Satisfactory comparison of conductance measurements with electrodiffusion calculations.