Multiple inward channels provide flexibility in Na+/K+ discrimination at the plasma membrane of barley suspension culture cells
Multiple inward channels provide flexibility in Na+/K+ discrimination at the plasma membrane of barley suspension culture cells
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DOI：
10.1093/jxb/48.special_issue.481
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发表时间：
1997-03-01
影响因子：
6.9
通讯作者：
Sanders, D
中科院分区：
文献类型：
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作者：
Amtmann, A;Laurie, S;Sanders, D
在低盐（15 mM KCl）和高盐（另外150 mM NaCl）条件下研究了来自未成熟大麦胚的悬浮培养细胞质膜的离子转运，以了解植物在离子吸收过程中如何区分K+和Na+。在两种培养基中，约50%的细胞表现出静息电位比任何被动扩散电位更负。在全细胞膜片钳实验中，膜超极化激活了大的内向电流。虽然瞬时电流分量不区分K+和Na+，但时间依赖性电流I-in对K+的选择性超过Na+。进一步分析I-in具有以下性质：双指数电流激活（时间常数0.03 s和0.3 s，半激活电位类似于171 mV）;无灭活; Ba 2+完全阻断（30 mM，溶于100 mM KCl中），并被TEA部分阻断（+）（20 mM时最大50%）;依赖于细胞质ATP的毫摩尔浓度;不受外部或细胞质Na+的阻断。通过测定可逆电位和相对稳态电流，确定了选择性顺序为K+ >> Rb+ > NH 4 +> Na+ >> Cl-和K+ >> NH 4 + > Na+ > Rb+。P-NA：P-K为0.07+/-0.02（来自逆转电位），I-Na：I-K为0.17+/-0.05（来自相对电流）。所观察到的渗透率比之间的差异很大，这表明具有不同离子选择性的几个通道有助于时间依赖性的全细胞电流。在单通道实验中，发现了几种具有不同性质的内向通道，主要通道为电压门控的K+选择性通道（12 pS），ATP激活的非选择性阳离子通道（7 pS）和内向整流阴离子通道（150 pS，均为100 mM KCl的单位电导）。没有显着差异，发现在全细胞电流或单通道特性之间的细胞，已适应高盐生长培养基（150 mM NaCl）和非适应细胞。的想法，质膜离子通道的差异调节引起的生理灵活性，允许细胞在不同的外部条件下控制Na+的吸收，进行了讨论。
Ion transport across the plasma membrane of suspension-culture cells derived from immature barley embryos has been studied in low (15 mM KCl) and high (additional 150 mM NaCl) salt conditions to understand how plants discriminate between K+ and Na+ during ion uptake. In both media about 50% of the cells exhibited resting potentials more negative than any of the passive diffusion potentials. In whole-cell patch clamp experiments membrane hyperpolarization activated large inward currents. Whilst the instantaneous current components did not discriminate between K+ and Na+, the time-dependent current, I-in, was selective for K+ over Na+. Further analysis of I-in revealed the following properties: double exponential current activation (time-constants 0.03 s and 0.3 s, half activation potential similar to 171 mV); no inactivation; complete block by Ba2+ (30 mM in 100 mM KCl) and part block by TEA(+) (maximum 50% with 20 mM); dependence on millimolar concentrations of cytoplasmic ATP; no block by external or cytoplasmic Na+. The selectivity sequences K+ >> Rb+ > NH4+ > Na+ >> Cl- and K+ >> NH4+ > Na+ > Rb+ were determined from measurements of reversal potentials and relative steady-state currents respectively. P-NA:P-K was 0.07+/-0.02 (from reversal potentials) and I-Na:I-K was 0.17+/-0.05 (from relative currents). A high variance among the observed permeability ratios suggested that several channels with different ion-selectivities contributed to the time-dependent whole-cell currents. In single channel experiments, several inward channels with distinct properties were found. The major channels were voltage-gated, K+-selective channel (12 pS), (ii) an ATP-activated non-selective cation channel (7 pS) and (iii) an inward-rectifying anion-channel (150 pS, all unitary conductances given for 100 mM KCl). No significant differences were found in whole-cell currents or single-channel characteristics between cells that had been adapted to a high-salt growth-medium (150 mM NaCl) and non-adapted cells. The idea that differential regulation of plasma membrane ion channels gives rise to a physiological flexibility, allowing the cells to control Na+ uptake under varying external conditions, is discussed.