Non-Michaelis-Menten kinetics model for conductance of low-conductance potassium ion channels

作     者：Igor S. Tolokh Illya I. Tolokh Hee Cheol Cho Nazzareno D’Avanzo Peter H. Backx Saul Goldman C. G. Gray 

作者机构：Guelph-Waterloo Physics Institute University of Guelph Guelph Ontario Canada N1G 2W1 Department of Physiology and Medicine Heart and Stroke/Richard Lewar Center University of Toronto Toronto Ontario Canada M5S 3E2 Division of Cardiology University Health Network Toronto Ontario Canada M5G 2C4 Guelph-Waterloo Center for Graduate Work in Chemistry University of Guelph Guelph Ontario Canada N1G 2W1 

出 版 物：《Physical Review E》 (物理学评论E辑：统计、非线性和软体物理学)

年 卷 期：2005年第71卷第2期

页      面：021912-021912页

核心收录：

学科分类：07[理学] 070203[理学-原子与分子物理] 0702[理学-物理学] 

主　　题：SINGLE-FILE PORES K+ CHANNEL SELECTIVITY FILTER CRYSTAL-STRUCTURE MOLECULAR-BASIS PERMEATION SIMULATION TRANSPORT STATE KCSA 

摘      要：A reduced kinetics model is proposed for ion permeation in low-conductance potassium ion channels with zero net electrical charge in the selectivity filter region. The selectivity filter is assumed to be the only conductance-determining part of the channel. Ion entry and exit rate constants depend on the occupancy of the filter due to ion-ion interactions. The corresponding rates are assumed slow relative to the rates of ion motion between binding sites inside the filter, allowing a reduction of the kinetics model of the filter by averaging the entry and exit rate constants over the states with a particular occupancy number. The reduced kinetics model for low-conductance channels is described by only three states and two sets of effective rate constants characterizing transitions between these states. An explicit expression for the channel conductance as a function of symmetrical external ion concentration is derived under the assumption that the average electrical mobility of ions in the selectivity filter region in a limited range of ion concentrations does not depend on these concentrations. The simplified conductance model is shown to provide a good description of the experimentally observed conductance-concentration curve for the low-conductance potassium channel Kir2.1, and also predicts the mean occupancy of the selectivity filter of this channel. We find that at physiological external ion concentrations this occupancy is much lower than the value of two ions observed for one of the high-conductance potassium channels, KcsA.