Division of Inflammation Biology, La Jolla Institute for Allergy and Immunology, La Jolla, California, USA.
Biophys J. 2011 Apr 6;100(7):1697-707. doi: 10.1016/j.bpj.2011.02.038.
Low pulling forces applied locally to cell surface membranes produce viscoelastic cell surface protrusions. As the force increases, the membrane can locally separate from the cytoskeleton and a tether forms. Tethers can grow to great lengths exceeding the cell diameter. The protrusion-to-tether transition is known as the crossover. Here we propose a unified approach to protrusions and tethers providing, to our knowledge, new insights into their biomechanics. We derive a necessary and sufficient condition for a crossover to occur, a formula for predicting the crossover time, conditions for a tether to establish a dynamic equilibrium (characterized by constant nonzero pulling force and tether extension rate), a general formula for the tether material after crossover, and a general modeling method for tether pulling experiments. We introduce two general protrusion parameters, the spring constant and effective viscosity, valid before and after crossover. Their first estimates for neutrophils are 50 pN μm(-1) and 9 pN s μm(-1), respectively. The tether elongation after crossover is described as elongation of a viscoelastic-like material with a nonlinearly decaying spring (NLDs-viscoelastic material). Our model correctly describes the results of the published protrusion and tether pulling experiments, suggesting that it is universally applicable to such experiments.
局部施加于细胞膜表面的低拉力会产生具有粘弹性的细胞膜表面突起。随着力的增加，细胞膜可以与细胞骨架局部分离，形成连接物。连接物可以生长到超过细胞直径的极大长度。突起到连接物的转变被称为交叉。在这里，我们提出了一种统一的方法来处理突起和连接物，为它们的生物力学提供了新的见解。我们推导出了发生交叉的必要和充分条件，预测交叉时间的公式，连接物建立动态平衡的条件（以恒定的非零拉力和连接物延伸率为特征），交叉后的连接物材料的通用公式，以及连接物拉伸实验的通用建模方法。我们引入了两个一般的突起参数，即弹簧常数和有效粘度，它们分别在交叉前后有效。对于中性粒细胞，它们的初步估计值分别为 50 pN μm(-1)和 9 pN s μm(-1)。交叉后的连接物伸长被描述为具有非线性衰减弹簧（NLDs-粘弹性材料）的粘弹性材料的伸长。我们的模型正确地描述了已发表的突起和连接物拉伸实验的结果，表明它普遍适用于此类实验。
