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Inactivation and recovery in Kv1.4 K + channels: lipophilic interactions at the intracellular mouth of the pore
Author(s) -
Bett Glenna C. L.,
Rasmusson Randall L.
Publication year - 2004
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2003.055012
Subject(s) - chemistry , alanine , biophysics , intracellular , quinidine , valine , binding site , kcsa potassium channel , potassium channel , stereochemistry , point mutation , biochemistry , amino acid , mutation , ion channel , biology , receptor , gene , pharmacology
C‐type inactivation is present in many voltage‐gated potassium channels and is probably related to ‘slow’ inactivation in calcium and sodium channels. The mechanisms underlying C‐type inactivation are unclear, but it is sensitive to mutations on both the extra‐ and intracellular sides of the channel. We used an N‐terminal deleted channel with a valine to alanine point mutation at the intracellular side of S6 (fKv1.4[V561A]ΔN). This construct alters recovery from inactivation and inverts the relationship between C‐type inactivation and [K + ] o . We used this inverted relationship to examine C‐type inactivation and coupling mechanisms between N‐ and C‐type inactivation. The valine to alanine mutation reduces the channel's affinity for both quinidine and the N‐terminal domain. However, binding of the N‐terminal or quinidine restores normal recovery from inactivation. This suggests that coupling between N‐ and C‐type inactivation is dominated by allosteric mechanisms. The permeation mechanism, driven by a reduction in permeant [K + ] o following pore block (which would retard C‐type inactivation), contributes minimally to coupling in these channels. We propose that the cytoplasmic half of S6 forms part of the N‐terminal binding site, as previously predicted from X‐ray crystallography studies in the distantly related KcsA channel. Binding of the N‐terminal domain or a positively charged lipophilic compound such as quinidine interacts with the hydrophobic moieties on S6 in the bound state. This binding can orientate S6 into a conformation which resembles the normal C‐type inactivated state. This is the probable mechanism by which drug or N‐terminal binding increases the rate of C‐type inactivation via an allosteric mechanism.