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© The Rockefeller University Press, 0022-1295/1998//457/ $5.00
Journal of General Physiology, Volume 112, Number 4, 1998

Article

Intermediate Conductances during Deactivation of Heteromultimeric Shaker Potassium Channels

Jie Zheng and Fred J. Sigworth

From the Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut 06520

A previous study of the T442S mutant Shaker channel revealed activation-coupled subconductance levels that apparently represent kinetic intermediates in channel activation (Zheng, J., and F.J. Sigworth. 1997. J. Gen. Physiol. 110:101–117). We have now extended the study to heteromultimeric channels consisting of various numbers of mutant subunits as well as channels without mutant subunits, all in the background of a chimeric Shaker channel having increased conductance. It has been found that activation-coupled sublevels exist in all these channel types, and are traversed in at least 80% of all deactivation time courses. In symmetric K+ solutions, the currents in the two sublevels have a linear voltage dependence, being 23–44% and 54–70% of the fully open conductance. Sublevels in different channel types share similar voltage dependence of the mean lifetime and similar ion selectivity properties. However, the mean lifetime of each current level depends approximately geometrically on the number of mutant subunits in the channel, becoming shorter in channels having fewer mutant subunits. Each mutant subunit appears to stabilize all of the conducting states by ~0.5 kcal/mol. Consistent with previous results in the mutant channel, sublevels in channels with two or no mutant subunits also showed ion selectivities that differ from that of the fully open level, having relatively higher K+ than Rb+ conductances. A model is presented in which Shaker channels have two coupled activation gates, one associated with the selectivity filter and a second associated with the S6 helix bundle.

Key Words: ion channel gating • selectivity • subconductance • cooperativity • subunit stoichiometry

Address correspondence to F.J. Sigworth, Department of Cellular and Molecular Physiology, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06520. Fax: 203-785-4951; E-mail: fred.sigworth @yale.edu

Abbreviations: M, mutant subunit; W or WT, Shaker-mKv3.1 chimera


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B. S. Rothberg and K. L. Magleby
Gating Kinetics of Single Large-Conductance Ca2+-Activated K+ Channels in High Ca2+ Suggest a Two-Tiered Allosteric Gating Mechanism
J. Gen. Physiol., July 1, 1999; 114(1): 93 - 124.
[Abstract] [Full Text] [PDF]


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