Department of Physiology and Biophysics, University of Miami Miller School of Medicine Miami, FL, USA.
Department of Physiology and Biophysics, University of Miami Miller School of Medicine Miami, FL, USA ; Neuroscience Program, University of Miami Miller School of Medicine Miami, FL, USA.
Front Physiol. 2015 Jan 21;5:532. doi: 10.3389/fphys.2014.00532. eCollection 2014.
Single-channel kinetics has proven a powerful tool to reveal information about the gating mechanisms that control the opening and closing of ion channels. This introductory review focuses on the gating of large conductance Ca(2+)- and voltage-activated K(+) (BK or Slo1) channels at the single-channel level. It starts with single-channel current records and progresses to presentation and analysis of single-channel data and the development of gating mechanisms in terms of discrete state Markov (DSM) models. The DSM models are formulated in terms of the tetrameric modular structure of BK channels, consisting of a central transmembrane pore-gate domain (PGD) attached to four surrounding transmembrane voltage sensing domains (VSD) and a large intracellular cytosolic domain (CTD), also referred to as the gating ring. The modular structure and data analysis shows that the Ca(2+) and voltage dependent gating considered separately can each be approximated by 10-state two-tiered models with five closed states on the upper tier and five open states on the lower tier. The modular structure and joint Ca(2+) and voltage dependent gating are consistent with a 50 state two-tiered model with 25 closed states on the upper tier and 25 open states on the lower tier. Adding an additional tier of brief closed (flicker states) to the 10-state or 50-state models improved the description of the gating. For fixed experimental conditions a channel would gate in only a subset of the potential number of states. The detected number of states and the correlations between adjacent interval durations are consistent with the tiered models. The examined models can account for the single-channel kinetics and the bursting behavior of gating. Ca(2+) and voltage activate BK channels by predominantly increasing the effective opening rate of the channel with a smaller decrease in the effective closing rate. Ca(2+) and depolarization thus activate by mainly destabilizing the closed states.
单通道动力学已被证明是一种强大的工具，可以揭示控制离子通道开启和关闭的门控机制的信息。本综述重点介绍了大电导钙（Ca2+）和电压激活钾（K+）（BK 或 Slo1）通道在单通道水平下的门控机制。它从单通道电流记录开始，逐步介绍和分析单通道数据，并根据离散状态马尔可夫（DSM）模型来发展门控机制。DSM 模型是根据 BK 通道的四聚体模块结构来构建的，该结构由中央跨膜孔门控域（PGD）与四个周围的跨膜电压感应域（VSD）和一个大的细胞内胞质域（CTD）组成，也称为门控环。模块结构和数据分析表明，分别考虑的 Ca2+和电压依赖性门控可以分别用 10 状态双层模型来近似，上层有五个关闭状态，下层有五个开放状态。模块结构和联合 Ca2+和电压依赖性门控与具有上层 25 个关闭状态和下层 25 个开放状态的 50 状态双层模型一致。在 10 状态或 50 状态模型中添加额外的短暂关闭（闪烁状态）层可以改善门控的描述。在固定的实验条件下，通道只会在潜在状态数的一个子集中门控。检测到的状态数和相邻间隔持续时间之间的相关性与分层模型一致。所检查的模型可以解释单通道动力学和门控的突发行为。Ca2+和电压主要通过增加通道的有效开启率，同时减小有效关闭率来激活 BK 通道。因此，Ca2+和去极化主要通过使关闭状态失稳来激活。
