Das S, Reusch R N
Department of Microbiology, Michigan State University, East Lansing, MI 48824, USA.
J Membr Biol. 1999 Jul 15;170(2):135-45. doi: 10.1007/s002329900543.
Nonproteinaceous calcium channel complexes from Escherichia coli, composed of poly-(R)-3-hydroxybutyrate (PHB) and inorganic polyphosphate (polyP), exhibit two distinct gating modes (modes 1 and 2) in planar lipid bilayers. Here we report the kinetic characterization of the channel in mode 2, a mode characterized by two well-defined conductance levels, a fully open state (87 +/- 3 pS), and a major subconductance state (56 +/- 2 pS). Other subconductance states and full closures are rare (<0.5% of total time). Several kinetic properties of the channel showed asymmetric voltage-dependence indicating an asymmetry in the channel structure. Accordingly, single channels responded to potential change in one of two mirror-image patterns, postulated to arise from opposite orientations of the asymmetrical channel complex in the bilayer. The fraction of time spent in each conductance level was strongly voltage-sensitive. For channels reported in this study, presumably all oriented in the same direction, residence time in the fully open state increased as clamping potentials became more positive whereas residence time in the major subconductance state increased at more negative potentials. Analysis of open time distributions revealed existence of two kinetically distinct states for each level. The shorter time constants for both conductance states exhibited weak voltage-sensitivity; however, the longer time constants were strongly voltage-sensitive. A kinetic scheme, consistent with the complex voltage dependence of the channel, is proposed.
来自大肠杆菌的非蛋白质钙通道复合物，由聚（R）-3-羟基丁酸酯（PHB）和无机多聚磷酸盐（聚P）组成，在平面脂质双层中表现出两种不同的门控模式（模式1和模式2）。在此，我们报告模式2通道的动力学特征，该模式的特征是有两个明确的电导水平，一个完全开放状态（87±3 pS）和一个主要的亚电导状态（56±2 pS）。其他亚电导状态和完全关闭状态很少见（占总时间的<0.5%）。通道的几个动力学特性显示出不对称的电压依赖性，表明通道结构存在不对称性。因此，单通道以两种镜像模式之一对电位变化做出反应，推测这是由双层中不对称通道复合物的相反取向引起的。在每个电导水平所花费的时间比例对电压非常敏感。对于本研究中报道的通道，推测所有通道都朝同一方向取向，随着钳制电位变得更正，在完全开放状态下的停留时间增加，而在主要亚电导状态下的停留时间在更负的电位下增加。对开放时间分布的分析揭示了每个水平存在两种动力学上不同的状态。两种电导状态的较短时间常数表现出较弱的电压敏感性；然而，较长的时间常数对电压非常敏感。提出了一个与通道复杂的电压依赖性一致的动力学方案。
