Kinetic structure of large-conductance Ca2+-activated K+ channels suggests that the gating includes transitions through intermediate or secondary states. A mechanism for flickers.
Kinetic structure of large-conductance Ca2+-activated K+ channels suggests that the gating includes transitions through intermediate or secondary states. A mechanism for flickers.
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DOI：
10.1085/jgp.111.6.751
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发表时间：
1998-06
期刊：
影响因子：
--
通讯作者：
Magleby KL
中科院分区：
文献类型：
--
作者：
Rothberg BS;Magleby KL
用膜片钳技术记录了大鼠骨骼肌大电导钙激活钾通道的单通道电流，并对其进行了二维分析，探讨了钙依赖性门控的机制。为了提取和显示基本的动力学信息，动力学结构，从单通道电流，相邻的开放和封闭的间隔分组为对，并绘制为二维停留时间分布，和过度和赤字的间隔对超过预期的独立配对绘制为依赖图。动力学结构的基本特征是一般相同的单个大电导钙激活的K+通道，但通道特异性差异是显而易见的，这表明在门控的异质性。从Monod-Wyman-Changeux（MWC）模型中提取的简单门控方案可以近似动力学结构的Ca 2+依赖性的基本特征。然而，观察到的和预测的依赖图之间的一致差异表明，额外的短暂的生命周期封闭状态不包括在MWC型模型中涉及门控。添加这些额外的简短的封闭状态的MWC型模型，无论是超出激活途径（二级封闭状态）或激活途径内（中间封闭状态），改善了动力学结构的钙依赖性的描述。次级关闭状态与次级门或通道阻断的关闭一致。中间闭合状态与通道通过在更稳定的开放和闭合状态之间经过一系列中间构象而激活的机制一致。正是附加的次级或中间关闭状态引起了门控中的大多数短暂关闭（闪烁）。
Mechanisms for the Ca2+-dependent gating of single large-conductance Ca2+-activated K+ channels from cultured rat skeletal muscle were developed using two-dimensional analysis of single-channel currents recorded with the patch clamp technique. To extract and display the essential kinetic information, the kinetic structure, from the single channel currents, adjacent open and closed intervals were binned as pairs and plotted as two-dimensional dwell-time distributions, and the excesses and deficits of the interval pairs over that expected for independent pairing were plotted as dependency plots. The basic features of the kinetic structure were generally the same among single large-conductance Ca2+-activated K+ channels, but channel-specific differences were readily apparent, suggesting heterogeneities in the gating. Simple gating schemes drawn from the Monod- Wyman-Changeux (MWC) model for allosteric proteins could approximate the basic features of the Ca2+ dependence of the kinetic structure. However, consistent differences between the observed and predicted dependency plots suggested that additional brief lifetime closed states not included in MWC-type models were involved in the gating. Adding these additional brief closed states to the MWC-type models, either beyond the activation pathway (secondary closed states) or within the activation pathway (intermediate closed states), improved the description of the Ca2+ dependence of the kinetic structure. Secondary closed states are consistent with the closing of secondary gates or channel block. Intermediate closed states are consistent with mechanisms in which the channel activates by passing through a series of intermediate conformations between the more stable open and closed states. It is the added secondary or intermediate closed states that give rise to the majority of the brief closings (flickers) in the gating.