Schoppa N E, Sigworth F J
Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut 06520, USA.
J Gen Physiol. 1998 Feb;111(2):271-94. doi: 10.1085/jgp.111.2.271.
The conformational changes associated with activation gating in Shaker potassium channels are functionally characterized in patch-clamp recordings made from Xenopus laevis oocytes expressing Shaker channels with fast inactivation removed. Estimates of the forward and backward rates for transitions are obtained by fitting exponentials to macroscopic ionic and gating current relaxations at voltage extremes, where we assume that transitions are unidirectional. The assignment of different rates is facilitated by using voltage protocols that incorporate prepulses to preload channels into different distributions of states, yielding test currents that reflect different subsets of transitions. These data yield direct estimates of the rate constants and partial charges associated with three forward and three backward transitions, as well as estimates of the partial charges associated with other transitions. The partial charges correspond to an average charge movement of 0.5 e0 during each transition in the activation process. This value implies that activation gating involves a large number of transitions to account for the total gating charge displacement of 13 e0. The characterization of the gating transitions here forms the basis for constraining a detailed gating model to be described in a subsequent paper of this series.
与去除快速失活的Shaker钾通道激活门控相关的构象变化，在表达Shaker通道的非洲爪蟾卵母细胞的膜片钳记录中得到功能表征。通过将指数函数拟合到极端电压下的宏观离子电流和门控电流弛豫来获得转变的正向和反向速率估计值，在此我们假设转变是单向的。通过使用包含预脉冲的电压方案将通道预加载到不同的状态分布中，从而产生反映不同转变子集的测试电流，有助于对不同速率进行赋值。这些数据直接给出了与三个正向和三个反向转变相关的速率常数和部分电荷的估计值，以及与其他转变相关的部分电荷的估计值。部分电荷对应于激活过程中每次转变时平均0.5 e0的电荷移动。该值意味着激活门控涉及大量转变以解释13 e0的总门控电荷位移。这里对门控转变的表征构成了约束本系列后续论文中将要描述的详细门控模型的基础。
