Two Kir2.1 channel populations with different sensitivities to Mg2+ and polyamine block: a model for the cardiac strong inward rectifier K+ channel
Two Kir2.1 channel populations with different sensitivities to Mg2+ and polyamine block: a model for the cardiac strong inward rectifier K+ channel
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DOI：
10.1113/jphysiol.2004.079186
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发表时间：
2005-03
期刊：
影响因子：
--
通讯作者：
Ding-Hong Yan;K. Ishihara
中科院分区：
文献类型：
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作者：
Ding-Hong Yan;K. Ishihara
全细胞 Kir2.1 电流的强烈内向整流与心脏内向整流 K+ 电流 (IK1) 非常相似，是由细胞内多胺精胺和亚精胺对外向电流的电压依赖性阻断引起的。我们最近表明，在存在不同浓度的细胞质多胺的情况下，从内向外斑块获得的宏观 Kir2.1 电流可以通过对多胺阻断表现出不同敏感性的两个通道群的电流总和来很好地解释。用 5-10 μm 细胞质精胺获得的外向电流显示出与 IK1 类似的电流-电压关系，并且被认为主要流经表现出较低精胺敏感性的一小群通道。在这里，我们使用由内而外的贴片来检查在细胞质精胺不存在和存在的情况下细胞质 Mg2+ 对宏观 Kir2.1 电流的阻断。外向电流被 0.6 和 1.1 mm Mg2+ 以浓度依赖性方式阻断，但一小部分 (~0.1) 宏观电导在这些浓度下对 Mg2+ 具有抵抗力，表明存在两个对 Mg2+ 具有不同敏感性的 Kir2.1 通道群。此外，在这些浓度下，Mg2+通过诱导浅阻挡态来阻挡内向电流，该浅阻挡态与引起内向整流的深层阻挡态不同。在存在 1.1 mm Mg2++ 5 μm 精胺的情况下，Mg2+ 在去极化脉冲期间阻断了大量电流分量，并产生瞬态向外分量，这与早期全细胞实验的结果一致。在稳定状态下，Mg2+阻断了反转电位附近和负电压处的电流，并感应出持续的向外分量。稳态和时间依赖性电流幅度以及精胺和 Mg2+ 引起的部分阻断可以通过一个模型定量解释，其中 Mg2+ 与精胺竞争阻断高亲和力通道并诱导三种电导状态。目前的结果表明，外向 IK1 流经对细胞质阻断剂具有不同敏感性的两个通道群。
The strong inward rectification of the whole cell Kir2.1 current, which is very similar to the cardiac inward rectifier K+ current (IK1), is caused by voltage‐dependent blockade of outward currents by the intracellular polyamines spermine and spermidine. We recently showed that macroscopic Kir2.1 currents obtained from inside‐out patches in the presence of various concentrations of cytoplasmic polyamines are well explained by the sum of the currents through two populations of channels that show differing susceptibilities to polyamine blockade. The outward currents obtained with 5–10 μm cytoplasmic spermine showed current–voltage relationships similar to those of IK1 and were considered to flow mostly through a small population of channels exhibiting lower spermine sensitivity. Here we used inside‐out patches to examine the blockade of macroscopic Kir2.1 currents by cytoplasmic Mg2+ in the absence and presence of cytoplasmic spermine. Outward currents were blocked by 0.6 and 1.1 mm Mg2+ in a concentration‐dependent manner, but a small fraction (∼0.1) of the macroscopic conductance was resistant to Mg2+ at those concentrations, suggesting there are two populations of Kir2.1 channels with different sensitivities to Mg2+. Furthermore, at those concentrations, Mg2+ blocked inward currents by inducing a shallow blocked state that differed from the deeper state causing the inward rectification. In the presence of 1.1 mm Mg2++ 5 μm spermine, Mg2+ blocked a substantial current component during depolarizing pulses and generated transient outward components, which is consistent with findings from earlier whole‐cell experiments. In the steady state, Mg2+ blocked the currents at voltages around and negative to the reversal potential and induced sustained outward components. The steady‐state and time‐dependent current amplitudes and the fractional blockades caused by spermine and Mg2+ could be quantitatively explained by a model in which Mg2+ competes with spermine to block the high‐affinity channel and induces three conductance states. The present results suggest that the outward IK1 flows through two populations of channels with different sensitivities to cytoplasmic blockers.