title: Mechanism for attenuated outward conductance induced by mutations in the cytoplasmic pore of Kir2.1 channels.
abstract: Outward currents through Kir2.1 channels regulate the electrical properties of excitable cells. These currents are subject to voltage-dependent attenuation by the binding of polyamines to high- and low-affinity sites, which leads to inward rectification, thereby controlling cell excitability. To examine the effects of positive charges at the low-affinity site in the cytoplasmic pore on inward rectification, we studied a mutant Kir channel (E224K/H226E) and measured single-channel currents and streaming potentials (Vstream), the latter provide the ratio of water to ions queued in a single-file permeation process in the selectivity filter. The water-ion coupling ratio was near one at a high K(+) concentration ([K(+)]) for the wild-type channel and increased substantially as [K(+)] decreased. On the other hand, fewer ions occupied the selectivity filter in the mutant at all [K(+)]. A model for the Kir channel involving a K(+) binding site in the wide pore was introduced. Model analyses revealed that the rate constants associated with the binding and release to and from the wide-pore K(+) binding site was modified in the mutant. These effects lead to the reduced contribution of a conventional two-ion permeation mode to total conductance, especially at positive potentials, thereby inward rectification.
authors.affiliation: Institute of Biomedical Sciences, Academia Sinica, Taipei 11529, Taiwan, ROC.
authors.forename: Hsueh-Kai
authors.initials: HK
authors.lastname: Chang
authors.affiliation: Department of Molecular Physiology and Biophysics, University of Fukui Faculty of Medical Sciences, Eiheiji-cho, Yoshida-gun, Fukui 910-1193, Japan.
authors.forename: Masayuki
authors.initials: M
authors.lastname: Iwamoto
authors.affiliation: Department of Molecular Physiology and Biophysics, University of Fukui Faculty of Medical Sciences, Eiheiji-cho, Yoshida-gun, Fukui 910-1193, Japan.
authors.forename: Shigetoshi
authors.initials: S
authors.lastname: Oiki
authors.affiliation: Institute of Biomedical Sciences, Academia Sinica, Taipei 11529, Taiwan, ROC.
authors.forename: Ru-Chi
authors.initials: RC
authors.lastname: Shieh
mesh_terms: D000200:Action Potentials; D000818:Animals; D001665:Binding Sites; D002463:Cell Membrane Permeability; D003593:Cytoplasm / Q000737:chemistry / Q000378:metabolism*; D007477:Ions / Q000737:chemistry / Q000378:metabolism; D008390:Markov Chains; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D009865:Oocytes / Q000378:metabolism; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism; D024661:Potassium Channels, Inwardly Rectifying / Q000235:genetics* / Q000378:metabolism*; D014981:Xenopus / Q000254:growth & development / Q000378:metabolism
chemical_list: D007477:Ions; C489461:Kir2.1 channel; D024661:Potassium Channels, Inwardly Rectifying; D011188:Potassium