Department of Physics, Sungkyunkwan University, Suwon 440-746, Korea.
J Phys Condens Matter. 2010 Feb 17;22(6):062101. doi: 10.1088/0953-8984/22/6/062101. Epub 2010 Jan 22.
We study the mechanical properties of ternary lipid bilayers assembled in giant vesicles, formed from a saturated and an unsaturated phosphocholine (in equal proportions) and cholesterol. As a function of temperature, these systems can undergo in-plane phase separation. Using image analysis we identify the vesicle contour, and quantify the vesicle shape and the amplitude of membrane thermal fluctuations. The two lipid compositions chosen show different thermotropic behaviours. At 60 mol% cholesterol the membrane is in a uniform liquid state over the entire temperature range investigated (10-50 °C), but vesicles containing 30 mol% cholesterol undergo phase separation into two immiscible liquid phases at around 28 °C. Upon cooling below this transition temperature we observe a marked increase in the measured bending elastic modulus. Phase separation proceeds over a long time (tens of minutes), and we measure the properties of vesicles both during the domain coarsening phase and in the fully phase separated condition. Fluorescence microscopy allows us to identify the coexisting phases. We can therefore measure directly the bending moduli of each of the phases as a function of temperature, showing a strong variation which is attributed to the changing phospholipid and cholesterol composition.
我们研究了在巨大囊泡中组装的三元脂质双层的力学性质，这些囊泡由饱和和不饱和的磷酰胆碱（比例相等）和胆固醇组成。作为温度的函数，这些系统可以发生面内相分离。我们使用图像分析来确定囊泡的轮廓，并量化囊泡的形状和膜热涨落的幅度。所选择的两种脂质组成具有不同的热致性行为。在胆固醇 60mol%的情况下，膜在整个研究温度范围内（10-50°C）处于均匀液态，但含有 30mol%胆固醇的囊泡在约 28°C 时会发生相分离，形成两个不混溶的液相。在低于这个转变温度的冷却过程中，我们观察到测量的弯曲弹性模量显著增加。相分离进行了很长时间（数十分钟），我们在畴粗化阶段和完全相分离状态下测量了囊泡的性质。荧光显微镜允许我们识别共存相。因此，我们可以直接测量每个相的弯曲模量作为温度的函数，显示出强烈的变化，这归因于磷脂和胆固醇组成的变化。
