title: KcsA: it's a potassium channel.
abstract: Ion conduction and selectivity properties of KcsA, a bacterial ion channel of known structure, were studied in a planar lipid bilayer system at the single-channel level. Selectivity sequences for permeant ions were determined by symmetrical solution conductance (K(+) > Rb(+), NH(4)(+), Tl(+) >> Cs(+), Na(+), Li(+)) and by reversal potentials under bi-ionic or mixed-ion conditions (Tl(+) > K(+) > Rb(+) > NH(4)(+) >> Na(+), Li(+)). Determination of reversal potentials with submillivolt accuracy shows that K(+) is over 150-fold more permeant than Na(+). Variation of conductance with concentration under symmetrical salt conditions is complex, with at least two ion-binding processes revealing themselves: a high affinity process below 20 mM and a low affinity process over the range 100-1,000 mM. These properties are analogous to those seen in many eukaryotic K(+) channels, and they establish KcsA as a faithful structural model for ion permeation in eukaryotic K(+) channels.
authors.affiliation: Department of Biochemistry, Howard Hughes Medical Institute, Brandeis University, Waltham, MA 02454, USA.
authors.forename: M
authors.initials: M
authors.lastname: LeMasurier
authors.forename: L
authors.initials: L
authors.lastname: Heginbotham
authors.forename: C
authors.initials: C
authors.lastname: Miller
mesh_terms: D000465:Algorithms; D001426:Bacterial Proteins; D002412:Cations / Q000378:metabolism; D004594:Electrophysiology; D004926:Escherichia coli / Q000378:metabolism; D007700:Kinetics; D011188:Potassium / Q000378:metabolism; D015221:Potassium Channels / Q000302:isolation & purification / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D002412:Cations; D015221:Potassium Channels; C107790:prokaryotic potassium channel; D011188:Potassium