Selectivity and permeation in calcium release channel of cardiac muscle: Alkali metal ions
Selectivity and permeation in calcium release channel of cardiac muscle: Alkali metal ions
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DOI：
10.1016/s0006-3495(99)77297-8
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发表时间：
1999-03-01
影响因子：
3.4
通讯作者：
Eisenberg, B
中科院分区：
文献类型：
--
作者：
Chen, DP;Xu, L;Eisenberg, B
在碱金属离子Li+、K+、Na+、Rb+、Cs+的纯溶液和混合溶液(如双离子条件)中，从心肌肌浆网钙释放通道(CRC)的单个开放通道(在+/-180 mV范围内)测量电流。通过扩展Poisson-Nernst-Planck(PNP)电扩散公式分析电流-电压(I-V)关系，其中包括由化学势偏移量描述的局部化学相互作用，这可能反映了渗透进入/退出步骤中脱水/溶剂化/再水化能量的差异。该理论适用于所有数据，但只需很少的可调参数：每个离子物种的扩散系数，孔壁上的平均有效电荷分布，以及锂离子和钠离子的化学势偏移量。特别是，该理论解释了在双离子条件下，由电导序列定义的“选择性”和由渗透率(即反转电位)确定的“选择性”之间的差异。扩展的PNP配方似乎提供了选择性和渗透性的成功组合处理。这种通道的电导选择性主要是由摩擦引起的：不同种类的离子在通道中的扩散系数不同。离子的渗透选择性由其电化学势梯度和与通道的局部化学相互作用决定。这两种选择性(在CRC中)似乎都不涉及不同离子与通道蛋白的不同静电相互作用，即使这些离子的直径差别很大。
Current was measured from single open channels of the calcium release channel (CRC) of cardiac sarcoplasmic reticulum (over the range +/-180 mV) in pure and mixed solutions (e.g., biionic conditions) of the alkali metal ions Li+, K+, Na+, Rb+, Cs+, ranging in concentration from 25 mM to 2 M. The current-voltage (I-V) relations were analyzed by an extension of the Poisson-Nernst-Planck (PNP) formulation of electrodiffusion, which includes local chemical interaction described by an offset in chemical potential, which likely reflects the difference in dehydration/solvation/rehydration energies in the entry/exit steps of permeation. The theory fits all of the data with few adjustable parameters: the diffusion coefficient of each ion species, the average effective charge distribution on the wall of the pore, and an offset in chemical potential for lithium and sodium ions. In particular, the theory explains the discrepancy between "selectivities" defined by conductance sequence and "selectivities" determined by the permeability ratios (i.e., reversal potentials) in biionic conditions. The extended PNP formulation seems to offer a successful combined treatment of selectivity and permeation. Conductance selectivity in this channel arises mostly from friction: different species of ions have different diffusion coefficients in the channel. Permeability selectivity of an ion is determined by its electrochemical potential gradient and local chemical interaction with the channel. Neither selectivity (in CRC) seems to involve different electrostatic interaction of different ions with the channel protein, even though the ions have widely varying diameters.