Hahin R
Biological Sciences Department, Northern Illinois University, DeKalb 60115.
J Gen Physiol. 1988 Sep;92(3):331-50. doi: 10.1085/jgp.92.3.331.
The kinetic properties of the closing of Na channels were studied in frog skeletal muscle to obtain information about the dependence of channel closing on the past history of the channel. Channel closing was studied in normal and modified channels. Chloramine-T was used to modify the channels so that inactivation was virtually removed. A series of depolarizing prepulse potentials was used to activate Na channels, and a -140-mV postpulse was used to monitor the closing of the channels. Unmodified channels decay via a biexponential process with time constants of 72 and 534 microseconds at 12 degrees C. The observed time constants do not depend upon the potential used to activate the channels. The contribution of the slow component to the total decay increases as the activating prepulse is lengthened. After inactivation is removed, the biexponential character of the decay is retained, with no change in the magnitude of the time constants. However, increases in the duration of the activating prepulse over the range where the current is maximal 1-75 ms) produce identical biexponential decays. The presence of biexponential decays suggests that either two subtypes of Na channels are found in muscle, or Na channels can exist in one of two equally conductive states. The time-invariant decays observed suggest that channel closure does not depend upon their past history.
为了获取有关钠通道关闭对其过去经历的依赖性的信息，研究了青蛙骨骼肌中钠通道关闭的动力学特性。在正常通道和经过修饰的通道中研究了通道关闭情况。使用氯胺-T修饰通道，使得失活几乎被消除。一系列去极化预脉冲电位用于激活钠通道，而-140 mV的后脉冲用于监测通道的关闭。在12℃时，未修饰的通道通过双指数过程衰减，时间常数分别为72和534微秒。观察到的时间常数不取决于用于激活通道的电位。随着激活预脉冲的延长，慢成分对总衰减的贡献增加。失活消除后，衰减的双指数特征得以保留，时间常数的大小没有变化。然而，在电流最大的范围内（1 - 75毫秒），激活预脉冲持续时间的增加会产生相同的双指数衰减。双指数衰减的存在表明，要么在肌肉中发现了两种亚型的钠通道，要么钠通道可以存在于两种同等传导状态之一。观察到的时间不变衰减表明通道关闭不取决于它们的过去经历。
