Mathes C, Rosenthal J J, Armstrong G M, Gilly W F
Hopkins Marine Station, Department of Biological Sciences, Stanford University, Pacific Grove, California 93950, USA.
J Gen Physiol. 1997 Apr;109(4):435-48. doi: 10.1085/jgp.109.4.435.
Inactivation of delayed rectifier K conductance (gk) was studied in squid giant axons and in the somata of giant fiber lobe (GFL) neurons. Axon measurements were made with an axial wire voltage clamp by pulsing to VK (approximately -10 mV in 50-70 mM external K) for a variable time and then assaying available gK with a strong, brief test pulse. GFL cells were studied with whole-cell patch clamp using the same prepulse procedure as well as with long depolarizations. Under our experimental conditions (12-18 degrees C, 4 mM internal MgATP) a large fraction of gK inactivates within 250 ms at -10 mV in both cell bodies and axons, although inactivation tends to be more complete in cell bodies. Inactivation in both preparations shows two kinetic components. The faster component is more temperature-sensitive and becomes very prominent above 12 degrees C. Contribution of the fast component to inactivation shows a similar voltage dependence to that of gK, suggesting a strong coupling of this inactivation path to the open state. Omission of internal MgATP or application of internal protease reduces the amount of fast inactivation. High external K decreases the amount of rapidly inactivating IK but does not greatly alter inactivation kinetics. Neither external nor internal tetraethylammonium has a marked effect on inactivation kinetics. Squid delayed rectifier K channels in GFL cell bodies and giant axons thus share complex fast inactivation properties that do not closely resemble those associated with either C-type or N-type inactivation of cloned Kvl channels studied in heterologous expression systems.
在枪乌贼巨轴突和巨纤维叶（GFL）神经元的胞体中研究了延迟整流钾电导（gk）的失活情况。通过轴向丝电压钳对轴突进行测量，方法是向VK（在50 - 70 mM外部钾中约为-10 mV）脉冲不同时间，然后用一个强的、短暂的测试脉冲测定可用的gK。使用与轴突相同的预脉冲程序以及长时间去极化，通过全细胞膜片钳对GFL细胞进行研究。在我们的实验条件下（12 - 18℃，4 mM内部MgATP），在-10 mV时，胞体和轴突中的大部分gK在250 ms内失活，尽管胞体中的失活往往更完全。两种标本中的失活都显示出两个动力学成分。较快的成分对温度更敏感，在12℃以上变得非常显著。快速成分对失活的贡献显示出与gK相似的电压依赖性，表明这种失活途径与开放状态有很强的耦合。省略内部MgATP或应用内部蛋白酶会减少快速失活的量。高外部钾会减少快速失活的IK的量，但不会显著改变失活动力学。外部或内部四乙铵对失活动力学都没有明显影响。因此，GFL细胞胞体和巨轴突中的枪乌贼延迟整流钾通道具有复杂的快速失活特性，这些特性与在异源表达系统中研究的克隆Kvl通道的C型或N型失活不太相似。
