Two modes of polyamine block regulating the cardiac inward rectifier K+ current IK1 as revealed by a study of the Kir2.1 channel expressed in a human cell line
Two modes of polyamine block regulating the cardiac inward rectifier K+ current IK1 as revealed by a study of the Kir2.1 channel expressed in a human cell line
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DOI：
10.1113/jphysiol.2003.055434
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发表时间：
2004-04-01
影响因子：
5.5
通讯作者：
Ehara, T
中科院分区：
文献类型：
--
作者：
Ishihara, K;Ehara, T
强内向整流K+电流I-K1在接近反转电位的电压范围内显示出显著的外向电流幅度，从而在心脏动作电位的最后阶段引起快速复极。然而，产生外向I-K1的机制还不清楚。我们记录了电流从内向外补丁的HEK 293 T细胞，表达强内向整流K+通道Kir2.1和研究细胞质多胺，即精胺和亚精胺引起的电流的阻断。用5-10 μ m精胺或10-100 μ m亚精胺获得的Kir2.1的外向电流-电压（I-V）关系与I-K1的稳态外向I-V关系相似，在比反转电位正20 mV的水平处显示峰值，在更正的电压处具有负斜率。的关系表现出高原或双峰形状与1妈妈精胺/亚精胺或0.1妈妈精胺，分别。在弦电导-电压关系式中，在正电压范围内存在额外电导，不能用Boltzmann关系式来描述。额外的电导，其中产生的5-10妈妈精胺或10-100妈妈亚精胺的存在下，大部分的外向电流，定量解释了一个模型，认为两个群体的Kir2.1通道，这是由多胺阻断在一个高亲和力模式（模式1通道）或低亲和力模式（模式2通道）。测试脉冲后的内向尾电流的分析表明，从Kir2.1的精胺块的救济包括一个指数分量和一个几乎瞬时的分量。两种组分的含量与模型计算的模式1和模式2中的堵塞物含量基本一致。模式1通道的总通道的估计比例为0.9与0.1-10妈妈精胺，0.75与1-100妈妈亚精胺，和0.75和0.9之间时，精胺和亚精胺共存。精胺/亚精胺与通道在细胞内的网站的相互作用出现修改的两个构象通道状态，允许不同模式的阻塞的平衡。我们的研究结果表明，外向I-K1主要是由多胺的亲和力较低的通道产生的。多胺可以调节外向I-K1的幅度，不仅通过阻断通道，而且通过改变对多胺阻断表现出不同敏感性的通道的比例。
The strong inward rectifier K+ current, I-K1, shows significant outward current amplitude in the voltage range near the reversal potential and thereby causes rapid repolarization at the final phase of cardiac action potentials. However, the mechanism that generates the outward I-K1 is not well understood. We recorded currents from the inside-out patches of HEK 293T cells that express the strong inward rectifier K+ channel Kir2.1 and studied the blockage of the currents caused by cytoplasmic polyamines, namely, spermine and spermidine. The outward current-voltage (I-V) relationships of Kir2.1, obtained with 5-10 mum spermine or 10-100 mum spermidine, were similar to the steady-state outward I-V relationship of I-K1, showing a peak at a level that is similar to20 mV more positive than the reversal potential, with a negative slope at more positive voltages. The relationships exhibited a plateau or a double-hump shape with 1 mum spermine/spermidine or 0.1 mum spermine, respectively. In the chord conductance-voltage relationships, there were extra conductances in the positive voltage range, which could not be described by the Boltzmann relations fitting the major part of the relationships. The extra conductances, which generated most of the outward currents in the presence of 5-10 mum spermine or 10-100 mum spermidine, were quantitatively explained by a model that considered two populations of Kir2.1 channels, which were blocked by polyamines in either a high-affinity mode (Mode 1 channel) or a low-affinity mode (Mode 2 channel). Analysis of the inward tail currents following test pulses indicated that the relief from the spermine block of Kir2.1 consisted of an exponential component and a virtually instantaneous component. The fractions of the two components nearly agreed with the fractions of the blockages in Mode 1 and Mode 2 calculated by the model. The estimated proportion of Mode 1 channels to total channels was 0.9 with 0.1-10 mum spermine, 0.75 with 1-100 mum spermidine, and between 0.75 and 0.9 when spermine and spermidine coexisted. An interaction of spermine/spermidine with the channel at an intracellular site appeared to modify the equilibrium of the two conformational channel states that allow different modes of blockage. Our results suggest that the outward I-K1 is primarily generated by channels with lower affinities for polyamines. Polyamines may regulate the amplitude of the outward I-K1, not only by blocking the channels but also by modifying the proportion of channels that show different sensitivities to the polyamine block.