脂质膜的非线性电导、整流和机械敏感通道的形成
Nonlinear conductance, rectification and mechanosensitive channel formation of lipid membranes
摘要：
有越来越多的证据表明，脂质双层显示导电性能。然而，当解释生物膜对电压变化的电响应时，它们通常被认为是惰性绝缘体。然而，在电压钳条件下的脂质双层不仅显示电流轨迹与离散的传导步骤无法区分的蛋白质通道的存在下。在电流-电压（I-V）图中，它们也可以显示向外整流，即，电压门控令人惊讶的是，这甚至在化学对称的脂质双层中也观察到了。在这里，我们调查这种现象，使用一个理论框架，模型电压对脂膜的电致伸缩效应的存在下，自发极化，这可以通过电压偏移在电气测量中识别。它可以由膜的不对称性引起，例如由膜的非零自发曲率引起。这种弯曲可以由经由挠曲电效应的电压引起，或者由跨膜的流体静压差引起。在这里，我们描述的I-V关系形成的贴片移液器位于靠近水表面的尖端处的脂质膜。我们在相对于空气/水面的不同深度进行测量，从而导致跨膜的不同压力梯度。观察到线性和非线性I-V曲线。非线性传导始终采取向外整流电流的形式。我们解释了两种机制的电导特性：一个泄漏电流与恒定的电导没有孔，和第二个过程，这是由于电压门控孔开放与通道样传导步骤的外观相关。在某些情况下，这些非线性I-V关系显示dI/dV为负的电压状态。这也是先前在钠通道存在下观察到的。...
英文摘要：
There is mounting evidence that lipid bilayers display conductive properties. However, when interpreting the electrical response of biological membranes to voltage changes, they are commonly considered as inert insulators. However, lipid bilayers under voltage-clamp conditions do not only display current traces with discrete conduction-steps indistinguishable from those attributed to the presence of protein channels. In current-voltage (I-V) plots they may also display outward rectification, i.e., voltage-gating. Surprisingly, this has even been observed in chemically symmetric lipid bilayers. Here, we investigate this phenomenon using a theoretical framework that models the electrostrictive effect of voltage on lipid membranes in the presence of a spontaneous polarization, which can be recognized by a voltage offset in electrical measurements. It can arise from an asymmetry of the membrane, for example from a nonzero spontaneous curvature of the membrane. This curvature can be caused by voltage via the flexoelectric effect, or by hydrostatic pressure differences across the membrane. Here, we describe I-V relations for lipid membranes formed at the tip of patch pipettes situated close to an aqueous surface. We measured at different depths relative to air/water surface, resulting in different pressure gradients across the membrane. Both linear and nonlinear I-V profiles were observed. Nonlinear conduction consistently takes the form of outward rectified currents. We explain the conductance properties by two mechanisms: One leak current with constant conductance without pores, and a second process that is due to voltage-gated pore opening correlating with the appearance of channel-like conduction steps. In some instances, these nonlinear I-V relations display a voltage regime in which dI/dV is negative. This has also been previously observed in the presence of sodium channels. ...
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