Yanagisawa Miho, Imai Masayuki, Masui Tomomi, Komura Shigeyuki, Ohta Takao
Department of Physics, Ochanomizu University, Bunkyo, Tokyo 112-8610, Japan.
Biophys J. 2007 Jan 1;92(1):115-25. doi: 10.1529/biophysj.106.087494. Epub 2006 Oct 6.
We have studied the growth dynamics of domains on ternary fluid vesicles composed of saturated (dipalmitoylphosphatidylcholine), unsaturated (dioleoylphosphatidylcholine) phosphatidylcholine lipids, and cholesterol using a fluorescence microscopy. The domain coarsening processes are classified into two types: normal coarsening and trapped coarsening. For the normal coarsening, the domains having flat circular shape grow in a diffusion-and-coalescence manner and phenomenologically the mean size grows as a power law of approximately t(2/3). The observed growth law is not described by a two-dimensional diffusion-and-coalescence growth mechanism following the Saffman and Delbrück theory, which may originate from the two-body hydrodynamic interactions between domains. For trapped coarsening, on the other hand, the domain coarsening is suppressed at a certain domain size because the repulsive interdomain interactions obstruct the coalescence of domains. The two-color imaging of the trapped domains reveals that the repulsive interactions are induced by the budding of domains. The model free energy consisting of the bending energy of domains, the bending energy of matrix, the line energy of domain boundary, and the translation energy of domains can describe the observed trapped coarsening. The trapping of domains is caused by the coupling between the phase separation and the membrane elasticity under the incompressibility constraint.
我们使用荧光显微镜研究了由饱和（二棕榈酰磷脂酰胆碱）、不饱和（二油酰磷脂酰胆碱）磷脂酰胆碱脂质和胆固醇组成的三元流体囊泡上畴的生长动力学。畴的粗化过程分为两种类型：正常粗化和捕获粗化。对于正常粗化，具有扁平圆形形状的畴以扩散和聚结的方式生长，从现象学上看，平均尺寸以约t(2/3)的幂律增长。观察到的生长规律不能用遵循萨夫曼和德尔布吕克理论的二维扩散和聚结合并生长机制来描述，这可能源于畴之间的两体流体动力学相互作用。另一方面，对于捕获粗化，由于畴间排斥相互作用阻碍了畴的聚结，畴粗化在一定畴尺寸下受到抑制。对捕获畴的双色成像表明，排斥相互作用是由畴的出芽诱导的。由畴的弯曲能、基质的弯曲能、畴边界的线能和畴的平移能组成的模型自由能可以描述观察到的捕获粗化。畴的捕获是由不可压缩性约束下相分离和膜弹性之间的耦合引起的。
