Kurachi Y, Noma A, Irisawa H
Pflugers Arch. 1981 Oct;391(4):261-6. doi: 10.1007/BF00581504.
Electrogenicity of the Na pump was demonstrated in rabbit A-V node cells by analyzing the K-induced hyperpolarization occurring after a short period of K-free perfusion. The transient hyperpolarization was abolished completely by strophanthidin (10(-5)M). The membrane slope conductance remained unchanged during the transient hyperpolarization. On perfusion of 50 mM K and K-free incubation the transient hyperpolarization reached --69 mV which was more negative than the expected EK (about --28 mV). The order of potencies of monovalent cations to activate the K site of the Na pump was Tl greater than Rb equal to K greater than NH4 equal to Cs greater than Li, which was similar to the sequence reported in the literature. Michaelis-Menten type activation of the K site of the Na pump was suggested from the relationship between the decay rate constant of the K-induced outward current transient and [K]o. These findings obviously indicate that the Na pump in the A-V node cells shares common characteristics with those of other excitable tissues. Direct contribution of the pump activity to the membrane potential under physiological conditions was suggested by a significant depolarization occurring immediately after application of strophanthidin.
通过分析在短时间无钾灌注后出现的钾诱导超极化，在兔房室结细胞中证实了钠泵的电生性。短暂超极化被毒毛花苷（10⁻⁵M）完全消除。在短暂超极化期间，膜斜率电导保持不变。在灌注50 mM钾并进行无钾孵育时，短暂超极化达到-69 mV，比预期的钾平衡电位（约-28 mV）更负。单价阳离子激活钠泵钾位点的效力顺序为铊＞铷 = 钾＞铵 = 铯＞锂，这与文献报道的序列相似。从钾诱导外向电流瞬变的衰减速率常数与细胞外钾浓度[K]o的关系中，提示钠泵钾位点存在米氏型激活。这些发现明显表明，房室结细胞中的钠泵与其他可兴奋组织的钠泵具有共同特征。毒毛花苷应用后立即出现的显著去极化提示，在生理条件下泵活动对膜电位有直接贡献。
