Mutations of the pore-region residue T442 in Shaker channels result in large effects on channel kinetics. We studied mutations at this position in the backgrounds of NH2-terminal–truncated Shaker H4 and a Shaker -NGK2 chimeric channel having high conductance (Lopez, G.A., Y.N. Jan, and L.Y. Jan. 1994. Nature (Lond.). 367: 179–182). While mutations of T442 to C, D, H, V, or Y resulted in undetectable expression in Xenopus oocytes, S and G mutants yielded functional channels having deactivation time constants and channel open times two to three orders of magnitude longer than those of the parental channel. Activation time courses at depolarized potentials were unaffected by the mutations, as were first-latency distributions in the T442S chimeric channel. The mutant channels show two subconductance levels, 37 and 70% of full conductance. From single-channel analysis, we concluded that channels always pass through the larger subconductance state on the way to and from the open state. The smaller subconductance state is traversed in ∼40% of activation time courses. These states apparently represent kinetic intermediates in channel gating having voltage-dependent transitions with apparent charge movements of ∼1.6 e0. The fully open T442S chimeric channel has the conductance sequence Rb+ > NH4+ > K+. The opposite conductance sequence, K+ > NH4+ > Rb+, is observed in each of the subconductance states, with the smaller subconductance state discriminating most strongly against Rb+.
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1 August 1997
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August 01 1997
Selectivity Changes during Activation of Mutant Shaker Potassium Channels
Jie Zheng,
Jie Zheng
From the Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut 06520
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Fred J. Sigworth
Fred J. Sigworth
From the Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut 06520
Search for other works by this author on:
Jie Zheng
From the Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut 06520
Fred J. Sigworth
From the Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut 06520
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: [email protected]
1
Abbreviations used in this paper: NMDG, N -methyl-d-glucamine; TEA, tetraethylammonium.
Received:
February 10 1997
Accepted:
May 20 1997
Online ISSN: 1540-7748
Print ISSN: 0022-1295
1997
J Gen Physiol (1997) 110 (2): 101–117.
Article history
Received:
February 10 1997
Accepted:
May 20 1997
Citation
Jie Zheng, Fred J. Sigworth; Selectivity Changes during Activation of Mutant Shaker Potassium Channels . J Gen Physiol 1 August 1997; 110 (2): 101–117. doi: https://doi.org/10.1085/jgp.110.2.101
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