Keynes R D, Meves H, Hof D
Physiological Laboratory, University of Cambridge, U.K.
Proc Biol Sci. 1992 Jul 22;249(1324):101-6. doi: 10.1098/rspb.1992.0090.
Voltage-clamp recordings of INa in squid axons dialysed with Cs or TMA, and bathed in low Na choline seawater, showed that, except close to threshold, the initial peak of fast-inactivating current was invariably decreased by TMA, whereas the non-inactivating current in the steady state was simultaneously increased. The results suggest that although TMA does not act directly on the movements of the voltage sensors that activate the sodium system, it blocks single-channel conductance in a voltage-dependent fashion in both the open states of the Na channel, while it has an entirely different type of action by increasing the probability of late openings in the steady state. Another difference between the two open states was that the sodium permeability coefficient had a Q10 of 1.8 in the initial open state, whereas in the steady state the effect of temperature was much smaller or even negative.
在以铯或四甲基铵透析并浸浴在低钠胆碱海水中的枪乌贼轴突上进行的钠电流电压钳记录显示，除了接近阈值时，快速失活电流的初始峰值总是被四甲基铵降低，而稳态下的非失活电流同时增加。结果表明，虽然四甲基铵并不直接作用于激活钠系统的电压传感器的运动，但它在钠通道的开放状态下以电压依赖性方式阻断单通道电导，同时它通过增加稳态下后期开放的概率具有完全不同类型的作用。两种开放状态之间的另一个差异是，钠通透系数在初始开放状态下的Q10为1.8，而在稳态下温度的影响要小得多甚至为负。
