Levitt D G
Department of Physiology, University of Minnesota, Minneapolis 55455.
Biophys J. 1989 Mar;55(3):489-98. doi: 10.1016/S0006-3495(89)82842-5.
It is assumed that the conformational change of the voltage-gated channel is continuous, characterized by movement along a generalized one-dimensional reaction coordinate, x, varying from 0 to 1. This large conformational change is coupled to the movement of most of the gating charge. Superimposed on this large movement is a smaller, very fast conformational change that opens or closes the channel. The large conformational change perturbs the channel so that opening is favored near x = 1 and closing is favored near x = 0. The movement along the x axis is described by a generalized Nernst-Planck equation, whereas the open-close transition is modeled as a discrete reaction-rate process. The macroscopic conductance, gating current, and single-channel behavior of a simple, linearized version of the model is described. Although the model has only seven adjustable constants (about the same as would be required for a conventional three-state model), it can mimic the behavior of the delayed rectified K+ channel with 12 or more closed states. The single-channel behavior of the model can have bursts of rapid openings and closings, separated by long closed times. If the conformational change is assumed to correspond to the rotation and translation of charged helices, then this model can be used to estimate the effective rotational diffusion coefficient of the helix. Such calculations for the delayed rectifier K+ channel indicate that the motion must be very restricted.
假定电压门控通道的构象变化是连续的，其特征是沿着广义的一维反应坐标x移动，x的取值范围是0到1。这种大的构象变化与大部分门控电荷的移动相耦合。叠加在这种大的移动之上的是一个较小的、非常快速的构象变化，它打开或关闭通道。大的构象变化使通道受到扰动，因此在x = 1附近有利于通道开放，而在x = 0附近有利于通道关闭。沿着x轴的移动由广义能斯特 - 普朗克方程描述，而开放 - 关闭转变则被建模为一个离散的反应速率过程。描述了该模型简单线性化版本的宏观电导、门控电流和单通道行为。尽管该模型只有七个可调常数（与传统三态模型所需的常数数量大致相同），但它可以模拟具有12个或更多关闭状态的延迟整流钾通道的行为。该模型的单通道行为可以有快速开放和关闭的爆发，中间间隔较长的关闭时间。如果假定构象变化对应于带电螺旋的旋转和平移，那么这个模型可以用来估计螺旋的有效旋转扩散系数。对延迟整流钾通道的此类计算表明，这种运动必须受到非常严格的限制。
