Influence of chloride, potassium, and tetraethylammonium on the early outward current of sheep cardiac Purkinje fibers.
Influence of chloride, potassium, and tetraethylammonium on the early outward current of sheep cardiac Purkinje fibers.
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DOI：
10.1085/jgp.73.2.117
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发表时间：
1979-02
期刊：
影响因子：
--
通讯作者：
Gibbons WR
中科院分区：
文献类型：
--
作者：
Kenyon JL;Gibbons WR
在心脏浦肯野纤维的电压钳研究中，在去极化至比-20 mV更正的电压期间始终观察到大的早期外向电流。在外向电流峰值后，总膜电流缓慢下降。Dudel等人（1967. Pfluegers Arch. Eur. J.Physiol.294：197- 212）降低了细胞外氯离子浓度，并发现电流的外向峰和下降被消除。他们的结论是，在这些电压下的总膜电流在很大程度上取决于膜氯离子电导的时间和电压依赖性变化。我们重新研究了该电流的氯化物灵敏度，注意将可能的误差源降至最低。当细胞外氯离子浓度降低到对照的8.6%时，主要效应是外向电流的峰值幅度降低20%。这意味着膜氯离子电导不是这些电压下总电流的主要决定因素。在细胞外氯离子或钾离子浓度的改变后，短期条件去极化后获得的电流尾部的反转电位没有改变。我们怀疑尾电流包含内向和外向成分，净尾电流的表观反转电位在很大程度上反映了外向成分的动力学，因此本实验并不排除钾作为可能的电荷载体。钾携带大部分早期外向电流的可能性使用四乙基铵进一步研究，四乙基铵阻断神经和骨骼肌中的钾电流。这种药物大大减少了早期外向电流，这表明大部分早期外向电流是由钾离子携带的。
In voltage clamp studies of cardiac Purkinje fibers, a large early outward current is consistently observed during depolarizations to voltages more positive than -20 mV. After the outward peak of the current, the total membrane current declines slowly. Dudel et al. (1967. Pfluegers Arch. Eur. J. Physiol. 294:197--212) reduced the extracellular chloride concentration and found that the outward peak and the decline of the current were abolished. They concluded that the total membrane current at these voltages was largely determined by a time- and voltage-dependent change in the membrane chloride conductance. We reinvestigated the chloride sensitivity of this current, taking care to minimize possible sources of error. When the extracellular chloride concentration was reduced to 8.6% of control, the principal effect was a 20% decrease in the peak amplitude of the outward current. This implies that the membrane chloride conductance is not the major determinant of the total current at these voltages. The reversal potential of current tails obtained after a short conditioning depolarization was not changed by alterations in the extracellular chloride or potassium concentrations. We suspect that the tail currents contain both inward and outward components, and that the apparent reversal potential of the net tail current largely reflects the kinetics of the outward component, so that this experiment does not rule out potassium as a possible charge carrier. The possibility that potassium carries much of the early outward current was further investigated using tetraethylammonium, which blocks potassium currents in nerve and skeletal muscle. This drug substantially reduced the early outward current, which suggests that much of the early outward current is carried by potassium ions.