Brown A M, Lux H D, Wilson D L
J Gen Physiol. 1984 May;83(5):751-69. doi: 10.1085/jgp.83.5.751.
Activation and inactivation properties of Ca currents were investigated by studying the behavior of single Ca channels in snail neurons. The methods described in the previous paper were used. In addition, a zero-phase digital filter has been incorporated to improve the analysis of latencies to first opening, or waiting times. It was found that a decrease in the probability of single channel opening occurred with time. This was especially marked at 29 degrees C and paralleled the inactivation observed in macroscopic currents. The fact that a single channel was observed means that there is a significant amount of reopening from the "inactivated" state. Small depolarizations at 18 degrees C showed little inactivation. From these measurements, histograms of single channel open, closed, and waiting times were analyzed to estimate the rate constants of a three-state model of activation. Two serious discrepancies with the model were found. First, waiting time distributions at -20 mV were slower than those predicted by parameters obtained from an analysis of the single channel closed times. Second, it was shown that the time and the magnitude of the peak of the waiting time histogram were inconsistent with a three-state model. It is concluded that a minimum of four states are involved in activation. Some four-state models may be eliminated from further consideration. However, a comprehensive model of Ca channel kinetics must await further measurements.
通过研究蜗牛神经元中单个钙通道的行为，对钙电流的激活和失活特性进行了研究。采用了上一篇论文中描述的方法。此外，还加入了一个零相位数字滤波器，以改进对首次开放潜伏期或等待时间的分析。发现单通道开放概率随时间降低。这在29摄氏度时尤为明显，并且与宏观电流中观察到的失活情况相似。观察到单个通道这一事实意味着存在大量从“失活”状态重新开放的情况。18摄氏度时的小去极化显示几乎没有失活。通过这些测量，分析了单通道开放、关闭和等待时间的直方图，以估计激活三态模型的速率常数。发现了与该模型的两个严重差异。首先，-20 mV时的等待时间分布比通过分析单通道关闭时间获得的参数预测的要慢。其次，结果表明等待时间直方图峰值的时间和幅度与三态模型不一致。得出的结论是，激活过程至少涉及四个状态。一些四态模型可能无需进一步考虑。然而，钙通道动力学的综合模型必须等待进一步的测量。
