Chao N M, Young S H, Poo M M
Biophys J. 1981 Oct;36(1):139-53. doi: 10.1016/S0006-3495(81)84721-2.
Randomly distributed cell membrane components may become localized toward a specific region of the surface as a results of cell-cell contact or the cell's exposure to extracellular ligands. The mechanism for this localization process is unknown. In the present study, we investigated the plausibility of a passive mechanisms, namely that a local region of the cell surface serves as a "trap" for diffusing membrane proteins. Based on a model of spherical cell with a single circular trap on the surface, we derived the equation describing the surface density distribution and the average lifetime of the trappable molecules in the trap-free region of the membrane. This surface-trap theory was then used to analyze our experimental finding on the rapid localization of muscle surface soybean agglutinin receptors induced by cell-cell contact in culture. THe result indicates that the rate of localization of these receptors toward the cell-cell contact site can be accounted for by assuming that the receptors possess a diffusion coefficient of about 2.5 X10(-9) cm2/s (range: 1.2-9.3X10(-9) cm2/s) before they are trapped at the contact site. Independent measurement of the rate of lateral diffusion of these receptors yielded a lateral diffusion coefficient of about 1.9 X 10(-9) cm2/s (range 1.2-2.7 X10(-9) cm2/s), a value within the range of that predicted by the rate of localization. We thus conclude that lateral diffusion of mobile membrane components toward a local trap is a plausible mechanism for their localization induced by local surface modulation.
随机分布的细胞膜成分可能会由于细胞间接触或细胞暴露于细胞外配体而向表面的特定区域定位。这种定位过程的机制尚不清楚。在本研究中，我们研究了一种被动机制的合理性，即细胞表面的局部区域作为扩散膜蛋白的“陷阱”。基于一个表面有单个圆形陷阱的球形细胞模型，我们推导了描述表面密度分布以及膜无陷阱区域中可捕获分子平均寿命的方程。然后，这个表面陷阱理论被用于分析我们关于培养中细胞间接触诱导肌肉表面大豆凝集素受体快速定位的实验发现。结果表明，这些受体向细胞间接触位点的定位速率可以通过假设受体在被捕获到接触位点之前具有约2.5×10⁻⁹平方厘米/秒的扩散系数（范围：1.2 - 9.3×10⁻⁹平方厘米/秒）来解释。对这些受体横向扩散速率的独立测量得出横向扩散系数约为1.9×10⁻⁹平方厘米/秒（范围1.2 - 2.7×10⁻⁹平方厘米/秒），该值在由定位速率预测的范围内。因此，我们得出结论，可移动膜成分向局部陷阱的横向扩散是由局部表面调节诱导其定位的一种合理机制。
