Lu L, Montrose-Rafizadeh C, Hwang T C, Guggino W B
Department of Physiology, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205.
Biophys J. 1990 Jun;57(6):1117-23. doi: 10.1016/S0006-3495(90)82632-1.
A delayed voltage-dependent K+ current endogenous to Xenopus oocytes has been investigated by the voltage-clamp technique. Both activation and inactivation of the K+ current are voltage-dependent processes. The K+ currents were activated when membrane potential was depolarized from a holding potential of -90 to -50 mV. The peak current was reached within 150 ms at membrane potential of +30 mV. Voltage-dependent inactivation of the current was observed by depolarizing the membrane potential from -50 to 0 mV at 10-mV increments. Voltage-dependent inactivation was a slow process with a time constant of 16.5 s at -10 mV. Removal of Ca2+ from the bath has no effect on current amplitudes, which indicates that the current is Ca2+)-insensitive. Tail current analysis showed that reversal potentials were shifted by changing external K+ concentration, as would be expected for a K(+)-selective channel. The current was sensitive to quinine, a K+ channel blocker, with a Ki of 35 microM. The blockade of quinine is voltage-independent in the range of -20 to +60 mV. Whereas oocytes from the same animal have a relatively homogeneous current distribution, average amplitude of the K+ current varied among oocytes from different animals from 30 to 400 nA at membrane potential of +30 mV. Our results indicate the presence of the endogenous K+ current in Xenopus oocytes with characteristics of the delayed rectifier found in some nerve and muscle cells.
利用电压钳技术研究了非洲爪蟾卵母细胞内源性的延迟电压依赖性钾电流。钾电流的激活和失活都是电压依赖性过程。当膜电位从 -90 mV的钳制电位去极化到 -50 mV时，钾电流被激活。在膜电位为 +30 mV时，150 ms内达到峰值电流。通过以10 mV的增量将膜电位从 -50 mV去极化到0 mV，观察到电流的电压依赖性失活。电压依赖性失活是一个缓慢的过程，在 -10 mV时时间常数为16.5 s。从浴液中去除Ca2+对电流幅度没有影响，这表明该电流对Ca2+不敏感。尾电流分析表明，反转电位会随着外部K+浓度的变化而移动，这对于K+选择性通道来说是预期的。该电流对K+通道阻滞剂奎宁敏感，其抑制常数Ki为35 μM。在 -20至 +60 mV范围内，奎宁的阻断作用与电压无关。同一动物的卵母细胞具有相对均匀的电流分布，而在膜电位为 +30 mV时，不同动物的卵母细胞中钾电流的平均幅度在30至400 nA之间变化。我们的结果表明非洲爪蟾卵母细胞中存在内源性钾电流，其具有一些神经和肌肉细胞中发现的延迟整流器的特征。
