Talukder G, Aldrich R W
Department of Molecular and Cellular Physiology, Howard Hughes Medical Institute, Stanford University School of Medicine, Stanford, California 94305, USA.
Biophys J. 2000 Feb;78(2):761-72. doi: 10.1016/S0006-3495(00)76634-3.
study and characterization of unliganded openings is of central significance for the elucidation of gating mechanisms for allosteric ligand-gated ion channels. Unliganded openings have been reported for many channel types, but their low open probability can make it difficult to study their kinetics in detail. Because the large conductance calcium-activated potassium channel mSlo is sensitive to both intracellular calcium and to membrane potential, we have been able to obtain stable unliganded single-channel recordings of mSlo with relatively high opening probability. We have found that the single-channel gating behavior of mSlo is complex, with multiple open and closed states, even when no ligand is present. Our results rule out a Monod-Wyman-Changeux allosteric mechanism with a central voltage-dependent concerted step, and they support the existence of quaternary states with less than the full number of voltage sensors activated, as has been suggested by previous work involving measurements of gating currents.
对未结合配体时通道开放的研究和特性描述对于阐明变构配体门控离子通道的门控机制至关重要。许多通道类型都有未结合配体时通道开放的报道，但它们的低开放概率使得详细研究其动力学变得困难。由于大电导钙激活钾通道mSlo对细胞内钙和膜电位都敏感，我们得以获得具有相对较高开放概率的稳定的mSlo未结合配体单通道记录。我们发现，即使不存在配体，mSlo的单通道门控行为也很复杂，具有多个开放和关闭状态。我们的结果排除了具有中心电压依赖性协同步骤的Monod-Wyman-Changeux变构机制，并且支持存在少于全部数量电压传感器被激活的四级状态，正如先前涉及门控电流测量的研究所表明的那样。
