Janson L W, Ragsdale K, Luby-Phelps K
University of Texas Southwestern Medical Center at Dallas 75235-9040, USA.
Biophys J. 1996 Sep;71(3):1228-34. doi: 10.1016/S0006-3495(96)79367-0.
Subdomains of the cytoplasmic volume in tissue culture cells exclude large tracer particles relative to small. Evidence suggests that exclusion of the large particles is due to molecular sieving by the dense meshwork of microfilaments found in these compartments, but exclusion as a result of the close apposition of the dorsal and ventral plasma membrane of the cell in these regions has not been ruled out conclusively. In principle, these two mechanisms can be distinguished by the dependence of exclusion on tracer particle size. By fluorescence ratio imaging we have measured the partition coefficient (P/PO) into excluding compartments for tracer particles ranging in radius from 1 to 41 nm. The decay of P/PO as a function of particle radius is better fitted by three molecular sieving models than by a slit pore model. The sieving models predict a percolation cutoff radius of the order of 50 nm for partitioning into excluding compartments.
组织培养细胞中细胞质体积的亚结构域相对于小的示踪颗粒而言会排斥大的示踪颗粒。有证据表明，大颗粒的排斥是由于在这些区室中发现的微丝致密网络的分子筛分作用，但在这些区域中细胞背侧和腹侧质膜紧密贴附导致的排斥作用尚未被完全排除。原则上，这两种机制可以通过排斥对示踪颗粒大小的依赖性来区分。通过荧光比率成像，我们测量了半径从1到41 nm的示踪颗粒进入排斥区室的分配系数（P/PO）。与狭缝孔模型相比，P/PO随颗粒半径的衰减更好地拟合了三种分子筛分模型。筛分模型预测，进入排斥区室的渗透截止半径约为50 nm。
