Recent x-ray structures of bacterial Kcsa K+ channel revolutionized the ion channel science. A widely used theoretical model, based on the conception of discrete binding sites in the channel, appears to be inconsistent with the structural data. We developed a model of multiply occupied Kcsa-like selectivity filter based on the best available data. The model explicitly considers ion-ion interactions. Parameters of the ion-ion interactions,
such as shielding constant, are determined. The model correctly describes barrierless knock-on conduction in the filter and allows to study the influence of the large-scale filter motions on its properties. It is shown that the concerted motion of multiple ions in the filter may be described as a motion of single "quasi-ion " in the effective energy profile which is easily calculated numerically.