The Journal of General Physiology
Scientifica: Experts in Electrophysiology
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Published 1 September 2001. doi:10.1085/jgp.118.3.303
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© The Rockefeller University Press, 0022-1295/2001//303/ $5.00
Journal of General Physiology, Volume 118, Number 3, 2001


Original Article

Kcsa

It's a Potassium Channel



Meredith LeMasuriera, Lise Heginbothama, and Christopher Millera

a Department of Biochemistry, Howard Hughes Medical Institute, Brandeis University, Waltham, MA 02454
Department of Biochemistry, Howard Hughes Medical Institute, Brandeis University, Waltham, MA 02454.(781) 736-2365

cmiller{at}brandeis.edu

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+, NH4+, Tl+ >> Cs+, Na+, Li+) and by reversal potentials under bi-ionic or mixed-ion conditions (Tl+ > K+ > Rb+ > NH4+ >> 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.

Key Words: ion conductivity • selectivity


© 2001 The Rockefeller University Press


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