VOLTAGE-DEPENDENT MAGNESIUM BLOCK OF ADENOSINE-TRIPHOSPHATE-SENSITIVE POTASSIUM CHANNEL IN GUINEA-PIG VENTRICULAR CELLS
VOLTAGE-DEPENDENT MAGNESIUM BLOCK OF ADENOSINE-TRIPHOSPHATE-SENSITIVE POTASSIUM CHANNEL IN GUINEA-PIG VENTRICULAR CELLS
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DOI：
10.1113/jphysiol.1987.sp016572
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发表时间：
1987-06-01
影响因子：
5.5
通讯作者：
NOMA, A
中科院分区：
文献类型：
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作者：
HORIE, M;IRISAWA, H;NOMA, A
1.应用膜片钳技术的开放式细胞贴附结构，研究了豚鼠心室肌细胞内存在和不存在Mg ~（2+）或Na ~+时ATP敏感性K ~+通道的变化。2.细胞内微量Mg ~（2+）（[Mg ~（2+）]i）的存在使外向电流产生明显的波动，随着[Mg ~（2+）]i的增加，开放通道电流的幅度减小。内加钠离子也使外向电流的平均振幅降低，但电流噪声增加不明显。当膜电位从K+平衡电位（EK）向更正的方向移动时，这些效应变得更大。在电位负EK内向电流既不受内部Mg ~（2+）也不受Na ~+的影响。3.而外加Na+、Mg ~（2+）或Ca ~（2+）对单通道电流无影响。4.去除内部Mg 2+和Na+后，平均开放通道电流-电压关系几乎变为线性。参考这些未阻断的值，在不同水平的[Mg 2 +]i或[Na+]i下测定相对振幅。剂量-反应关系给出的希尔系数为. apprx。Mg 2+嵌段为1，Na+阻滞2例。Mg ~（2+）和Na ~+阻断的半峰浓度（Kh）随正电位的增加而降低。5.由内部Mg 2+诱导的开放通道电流噪声的功率密度谱显示出具有高于1 kHz的拐角频率的洛伦兹函数，这表明电流噪声是由于开放通道电流在阻断和未阻断状态之间的快速波动。角频率给出Mg 2+块和解块速率常数分别为107 M-1 s-1和104 s-1的顺序。6.随着外部K+浓度（[K+]0）从0增加到140 mM，电流波动变得不那么显著，并且Mg 2+阻断的Kh向更高的值移动。提高[K+]0增强了来自噪声分析的解阻断率，而阻断率没有显著改变。7.上述发现可以通过假设一个Mg 2+或两个Na+的结合位点位于通道内口跨膜电降的30-35%，从而导致K+通道的离子阻断来解释。在单通道电流-电压关系中观察到的明显向内整流归因于细胞内Mg 2+和/或Na+对通道的阻断。
1. The adenosine-5''-triphosphate (ATP)-sensitive K+ channel of guinea-pig ventricular cells was examined in the presence and absence of internal Mg2+ or Na+ using an open cell-attached configuration of the patch-clamp technique. 2. Millimolar concentrations of internal Mg2+ ([Mg2+]i) produced marked fluctuations in the outward current, and the amplitude of the open-channel current was reduced with increasing [Mg2+]i. Millimolar Na+ applied internally also decreased the mean amplitude of the outward current, but the increase in current noise was not obvious. These effects became larger when the membrane potential was shifted to be more positive from the K+ equilibrium potential (EK). At potentials negative to EK the inward current was affected by neither internal Mg2+ nor Na+. 3. The external application of Na+, Mg2+ or Ca2+, however, failed to affect the single-channel current. 4. After removal of both internal Mg2+ and Na+, the mean open-channel current-voltage relationship became virtually linear. Referring to these unblocked values, relative amplitudes were determined at different levels of [Mg2+]i or [Na+]i. The dose-response relations gave a Hill coefficient of .apprx. 1 for Mg2+ block and .apprx. 2 for Na+ block. The half-maximum concentrations (Kh) for both Mg2+ and Na+ block were shifted to lower values with increasing positive potentials. 5. The power-density spectrum of the open-channel current noise induced by internal Mg2+ showed a Lorentzian function with a corner frequency above 1 kHz, suggesting that the current noise is due to rapid fluctuations of open-channel current between blocked and unblocked states. The corner frequencies gave Mg2+ block and unblock rate constants which were of the order of 107 M-1 s-1 and 104 s-1, respectively. 6. With increasing external K+ concentration ([K+]0) from 0 to 140 mM the current fluctuations became less prominent, and Kh for Mg2+ block was shifted to higher values. Raising [K+]0 enhanced the unblock rate derived from the noise analysis while the block rate was not significantly altered. 7. The above findings could be explained by assuming a binding site for one Mg2+ or two Na+ located 30-35% of the electrical drop across the membrane from the inner mouth of the channel, thereby resulting in the ionic block of K+ passage. An apparent inward rectification observed in the single-channel current-voltage relation is attributable to the blockade of the channel by intracellular Mg2+ and/or Na+.