Noma A
Jpn J Physiol. 1976;26(6):619-30. doi: 10.2170/jjphysiol.26.619.
To determine the effect of high extracellular potassium concentration ([K]o) on the membrane current of the sinoatrial node cell, voltage clamp experiments were conducted using the double microelectrode technique. When depolarizing clamp pulses were applied, a transient inward current was followed by an outward current and an outward current tail flowed after the pulse. The amplitude of both the transient inward current and the outward current tail were markedly reduced with increasing [K]o, but the magnitude of the outward current during depolarization scarcely changed. The inward current during hyperpolarizing clamp pulses increased in magnitude at higher [K]o and the reversal potential for the inward current change decreased with increasing [K]o. From these results it was concluded that the suppression of the sinoatrial node automaticity at higher [K]o was due to the decrease in magnitude of both the transient inward current and the outward current tail. As the cause of the depression of the transient inward current, its inactivation through depolarization, increased outward leak current and some direct inhibitory effect of K were proposed. The reduction of the outward current tail was attributed to the decrease in the driving force of the K current.
为了确定高细胞外钾浓度（[K]o）对窦房结细胞膜电流的影响，采用双微电极技术进行了电压钳实验。当施加去极化钳制脉冲时，会出现一个瞬时内向电流，随后是一个外向电流，并且在脉冲后有一个外向电流尾。随着[K]o升高，瞬时内向电流和外向电流尾的幅度均显著降低，但去极化期间外向电流的大小几乎不变。在超极化钳制脉冲期间，内向电流的大小在较高的[K]o时增加，并且内向电流变化的反转电位随着[K]o升高而降低。从这些结果得出结论，在较高的[K]o时窦房结自律性的抑制是由于瞬时内向电流和外向电流尾的幅度均降低。作为瞬时内向电流降低的原因，提出了其通过去极化的失活、外向漏电流增加以及钾的一些直接抑制作用。外向电流尾的降低归因于钾电流驱动力的降低。
