蛙皮毒素修饰的枪乌贼巨轴突中钠离子通道的门控动力学。电压和温度效应。
Gating kinetics of batrachotoxin-modified Na+ channels in the squid giant axon. Voltage and temperature effects.
作者信息
Correa A M, Bezanilla F, Latorre R
机构信息
Department of Physiology, Ahmanson Laboratory of Neurobiology, University of California, Los Angeles 90024.
出版信息
Biophys J. 1992 May;61(5):1332-52. doi: 10.1016/S0006-3495(92)81941-0.
The gating kinetics of batrachotoxin-modified Na+ channels were studied in outside-out patches of axolemma from the squid giant axon by means of the cut-open axon technique. Single channel kinetics were characterized at different membrane voltages and temperatures. The probability of channel opening (Po) as a function of voltage was well described by a Boltzmann distribution with an equivalent number of gating particles of 3.58. The voltage at which the channel was open 50% of the time was a function of [Na+] and temperature. A decrease in the internal [Na+] induced a shift to the right of the Po vs. V curve, suggesting the presence of an integral negative fixed charge near the activation gate. An increase in temperature decreased Po, indicating a stabilization of the closed configuration of the channel and also a decrease in entropy upon channel opening. Probability density analysis of dwell times in the closed and open states of the channel at 0 degrees C revealed the presence of three closed and three open states. The slowest open kinetic component constituted only a small fraction of the total number of transitions and became negligible at voltages greater than -65 mV. Adjacent interval analysis showed that there is no correlation in the duration of successive open and closed events. Consistent with this analysis, maximum likelihood estimation of the rate constants for nine different single-channel models produced a preferred model (model 1) having a linear sequence of closed states and two open states emerging from the last closed state. The effect of temperature on the rate constants of model 1 was studied. An increase in temperature increased all rate constants; the shift in Po would be the result of an increase in the closing rates predominant over the change in the opening rates. The temperature study also provided the basis for building an energy diagram for the transitions between channel states.
采用切开轴突技术，在鱿鱼巨大轴突轴膜的外向膜片中研究了蛙毒素修饰的Na⁺通道的门控动力学。在不同膜电压和温度下对单通道动力学进行了表征。通道开放概率（Po）作为电压的函数，用等效门控粒子数为3.58的玻尔兹曼分布能很好地描述。通道在50%时间开放时的电压是[Na⁺]和温度的函数。内部[Na⁺]的降低导致Po与V曲线向右移动，表明激活门附近存在一个积分负固定电荷。温度升高会降低Po，这表明通道关闭构型的稳定，也表明通道开放时熵的降低。在0℃下对通道关闭和开放状态下的驻留时间进行概率密度分析，发现存在三个关闭状态和三个开放状态。最慢的开放动力学成分仅占总跃迁数的一小部分，在电压大于 -65 mV时可忽略不计。相邻间隔分析表明，连续开放和关闭事件的持续时间之间没有相关性。与此分析一致，对九个不同单通道模型的速率常数进行最大似然估计，得到一个优选模型（模型1），该模型具有线性的关闭状态序列和从最后一个关闭状态出现的两个开放状态。研究了温度对模型1速率常数的影响。温度升高会增加所有速率常数；Po的移动将是关闭速率增加占主导地位，超过开放速率变化的结果。温度研究还为构建通道状态之间跃迁的能量图提供了基础。
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