Yang Lewen, Kindt James T
Emory University , 1515 Dickey Drive, Atlanta, Georgia 30033, United States.
Langmuir. 2015 Feb 24;31(7):2187-95. doi: 10.1021/la504269t. Epub 2015 Feb 10.
When a range of lipid bilayers are melted to the disordered fluid phase from the (much less permeable) ordered gel phase, their permeability to a variety of permeants shows a peak at the transition temperature and drops off with increasing temperature, rather than just rising as melting proceeds. To explore this anomalous behavior, a simulated coarse-grained lipid membrane model that exhibits a phase transition upon expansion or compression was studied to determine how the permeation rate of a simple particle depends on the phase composition in the two-phase region and on particle size. The permeation rate and each phase's area fraction and area density could be directly calculated, along with the probability that the permeant would cross in either phase or in interfacial regions. For large permeants and system sizes, conditions could be found where permeability increases upon compression of the bilayer. Permeation was negligible in the gel phase and, in contrast to the predictions of the "leaky interface" hypothesis, was not enriched in interfacial regions. The anomalous effect could instead be attributed to an increase in the area per lipid of fluid-phase domains. This result motivated a model for the decrease in effective permeability barrier through fluid-phase domains arising from a decrease in the length of the gel/fluid interface at the midpoint of a permeation event.
当一系列脂质双层从（渗透性低得多的）有序凝胶相熔化为无序流体相时，它们对各种渗透物的渗透性在转变温度处出现峰值，并随温度升高而下降，而不是随着熔化的进行而仅仅上升。为了探究这种异常行为，研究了一种模拟的粗粒度脂质膜模型，该模型在膨胀或压缩时会发生相变，以确定简单粒子的渗透速率如何取决于两相区域中的相组成和粒子大小。可以直接计算渗透速率、各相的面积分数和面积密度，以及渗透物在任一相或界面区域穿过的概率。对于大的渗透物和系统尺寸，可以找到双层压缩时渗透率增加的条件。在凝胶相中渗透可忽略不计，并且与“渗漏界面”假说的预测相反，在界面区域中渗透并不富集。相反，这种异常效应可归因于流体相域中每个脂质面积的增加。这一结果促使我们建立了一个模型，用于解释在渗透事件中点处凝胶/流体界面长度的减小导致通过流体相域的有效渗透屏障降低的现象。
