||P.1457 right column bottom paragraph:"The puzzling feature of the ion filter is its very key properties: permeation and selectivity. A K+ channel can pass some 10^7 K+ per second and discriminate against the smaller Na+ at the same time (PK+ : PNa+ > 1,000 : 1). These properties challenge our common intuition about binding energy and binding specificity. The structure of the bacterial K+-channel, KcsA, readily explains these properties. The puzzling feature of the gate is how it can be controlled, and, in different channels, apparently controlled by all the known stimuli including ligands, second messengers, voltage, heat, and mechanical force. To more clearly summarize our current knowledge of cation channels, this review will first give a global view of the KcsA channel and then proceed with the description of its filter, its gate, and its lipid environment."