Zagotta W N, Hoshi T, Dittman J, Aldrich R W
Department of Molecular and Cellular Physiology, Howard Hughes Medical Institute, Stanford University School of Medicine, California 94305.
J Gen Physiol. 1994 Feb;103(2):279-319. doi: 10.1085/jgp.103.2.279.
Voltage-dependent gating behavior of Shaker potassium channels without N-type inactivation (ShB delta 6-46) expressed in Xenopus oocytes was studied. The voltage dependence of the steady-state open probability indicated that the activation process involves the movement of the equivalent of 12-16 electronic charges across the membrane. The sigmoidal kinetics of the activation process, which is maintained at depolarized voltages up to at least +100 mV indicate the presence of at least five sequential conformational changes before opening. The voltage dependence of the gating charge movement suggested that each elementary transition involves 3.5 electronic charges. The voltage dependence of the forward opening rate, as estimated by the single-channel first latency distribution, the final phase of the macroscopic ionic current activation, the ionic current reactivation and the ON gating current time course, showed movement of the equivalent of 0.3 to 0.5 electronic charges were associated with a large number of the activation transitions. The equivalent charge movement of 1.1 electronic charges was associated with the closing conformational change. The results were generally consistent with models involving a number of independent and identical transitions with a major exception that the first closing transition is slower than expected as indicated by tail current and OFF gating charge measurements.
研究了非洲爪蟾卵母细胞中表达的无N型失活的Shaker钾通道（ShB delta 6 - 46）的电压依赖性门控行为。稳态开放概率的电压依赖性表明，激活过程涉及相当于12 - 16个电子电荷跨膜移动。激活过程的S形动力学在高达至少 +100 mV的去极化电压下保持，表明在开放前至少存在五个连续的构象变化。门控电荷移动的电压依赖性表明每个基本转变涉及3.5个电子电荷。通过单通道首次延迟分布、宏观离子电流激活的最终阶段、离子电流再激活和导通门控电流时间进程估计的正向开放速率的电压依赖性表明，相当于0.3至0.5个电子电荷的移动与大量激活转变相关。1.1个电子电荷的等效电荷移动与关闭构象变化相关。结果总体上与涉及多个独立且相同转变的模型一致，但一个主要例外是，如尾电流和关断门控电荷测量所示，第一个关闭转变比预期慢。
