Allender David W, Schick M
Department of Physics, University of Washington, Seattle, WA 98195, USA.
Department of Physics, Kent State University, Kent, OH 44242, USA.
Membranes (Basel). 2020 Jul 28;10(8):167. doi: 10.3390/membranes10080167.
It is widely, but not universally, believed that the lipids of the plasma membrane are not uniformly distributed, but that "rafts" of sphingolipids and cholesterol float in a "sea" of unsaturated lipids. The physical origin of such heterogeneities is often attributed to a phase coexistence between the two different domains. We argue that this explanation is untenable for several reasons. Further, we note that the results of recent experiments are inconsistent with this picture. However, they are quite consistent with an alternate explanation, namely, that the plasma membrane is a microemulsion of the two kinds of regions. To show this, we briefly review a simplified version of this theory and its phase diagram. We also explicate the dependence of the predicted domain size on four physical parameters. They are the energy cost of gradients in the composition, the spontaneous curvature of the membrane, its bending modulus and its surface tension. Taking values of the latter two from experiment, we obtain domain sizes for several different cell types that vary from 58 to 88 nm.
人们普遍（但并非一致）认为，质膜中的脂质并非均匀分布，而是鞘脂和胆固醇的“筏”漂浮在不饱和脂质的“海洋”中。这种异质性的物理起源通常归因于两个不同区域之间的相共存。我们认为这种解释由于几个原因是站不住脚的。此外，我们注意到最近实验的结果与这种情况不一致。然而，它们与另一种解释相当一致，即质膜是这两种区域的微乳液。为了说明这一点，我们简要回顾一下该理论的简化版本及其相图。我们还阐述了预测的区域大小对四个物理参数的依赖性。它们是组成梯度的能量成本、膜的自发曲率、其弯曲模量和表面张力。根据实验得出的后两个参数的值，我们获得了几种不同细胞类型的区域大小，范围从58到88纳米。
