In cell membranes, the functional constituents such as peptides, proteins, and polysaccharides diffuse in a sea of lipids as single molecules and molecular aggregates. Thus, the fluidity of the heterogeneous multicomponent membrane is important for understanding the roles of the membrane in cell functionality. Recently, Henle and Levine described the hydrodynamics of molecular diffusion in a spherical membrane. A tangential point force at the north pole induces a pair of vortices whose centers lie on a line perpendicular to the point force and are symmetrical with respect to the point force. The position of the vortex center depends on ηm/Rηw, where R is the radius of the spherical membrane, and ηm and ηw are the viscosities of the membrane and the surrounding medium, respectively. Based on this theoretical prediction, we applied a point force to a phase-separated spherical vesicle composed of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine/1,2-dioleoyl-sn-glycero-3-phosphocholine/cholesterol by means of a microinjection technique. The pathlines were visualized by trajectories of microdomains. We determined the position of the vortex center and estimated the membrane viscosity using the dependence of the position of the vortex center on ηm/Rηw. The obtained apparent membrane viscosities for various compositions are mapped on the phase diagram. The membrane viscosity is almost constant in the range of 0 <φLo ≤ 0.5 (φLo: area fraction of the liquid ordered phase), whereas that in the range of 0.5 ≤ φLo < 1.0 exponentially increases with increase of φLo. The obtained viscosity landscape provides a basic understanding of the fluidity of heterogeneous multicomponent membranes.

中文翻译：

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相分离脂质膜的粘度景观。从流体速度场估计


在细胞膜中，肽、蛋白质和多糖等功能成分以单分子和分子聚集体的形式扩散在脂质海洋中。因此，异质多组分膜的流动性对于理解膜在细胞功能中的作用非常重要。最近，亨利和莱文描述了球形膜中分子扩散的流体动力学。北极处的切向点力引起一对涡旋，其中心位于垂直于点力的直线上并且关于点力对称。涡流中心的位置取决于 ηm/Rηw，其中 R 是球形膜的半径，ηm 和 ηw 分别是膜和周围介质的粘度。基于这一理论预测，我们对由 1,2-二棕榈酰-sn-甘油-3-磷酸胆碱/1,2-二油酰-sn-甘油-3-磷酸胆碱/胆固醇组成的相分离球形囊泡施加点力：显微注射技术的手段。路径通过微域的轨迹可视化。我们确定了涡流中心的位置，并利用涡流中心位置对 ηm/Rηw 的依赖性来估计膜粘度。所获得的各种组合物的表观膜粘度被绘制在相图上。膜粘度在 0 < φLo ≤ 0.5（φLo：液体有序相的面积分数）范围内几乎恒定，而在 0.5 ≤ φLo < 1.0 范围内，膜粘度随着 φLo 的增加呈指数增加。获得的粘度景观提供了对异质多组分膜的流动性的基本了解。