Smith M J, Berg E L, Lawrence M B
Department of Biomedical Engineering, University of Virginia School of Medicine and School of Engineering and Applied Science, Charlottesville, Virginia 22908, USA.
Biophys J. 1999 Dec;77(6):3371-83. doi: 10.1016/S0006-3495(99)77169-9.
Leukocyte capture and rolling on the vascular endothelium is mediated principally by the selectin family of cell adhesion receptors. In a parallel plate flow chamber, neutrophil rolling on purified selectins or a selectin-ligand substrate was resolved by high speed videomicroscopy as a series of ratchet-like steps with a characteristic time constant (Kaplanski, G., C. Farnarier, O. Tissot, A. Pierres, A.-M. Benoliel, M. C. Alessi, S. Kaplanski, and P. Bongrand. 1993. Biophys. J. 64:1922-1933; Alon, R., D. A. Hammer, and T. A. Springer. 1995. Nature (Lond.). 374:539-542). Under shear, neutrophil arrests due to bond formation events were as brief as 4 ms. Pause time distributions for neutrophils tethering on P-, E-, L-selectin, or peripheral node addressin (PNAd) were compared at estimated single bond forces ranging from 37 to 250 pN. Distributions of selectin mediated pause times were fit to a first order exponential, resulting in a molecular dissociation constant (k(off)) for the respective selectin as a function of force. At estimated single bond forces of 125 pN and below, all three selectin dissociation constants fit the Bell and Hookean spring models of force-driven bond breakage equivalently. Unstressed k(off) values based on the Bell model were 2.4, 2.6, 2.8, 3.8 s(-1) for P-selectin, E-selectin, L-selectin, and PNAd, respectively. Bond separation distances (reactive compliance) were 0.39, 0.18, 1.11, 0.59 A for P-selectin, E-selectin, L-selectin, and PNAd, respectively. Dissociation constants for L-selectin and P-selectin at single bond forces above 125 pN were considerably lower than either Bell or Hookean spring model predictions, suggesting the existence of two regimes of reactive compliance. Additionally, interactions between L-selectin and its leukocyte ligand(s) were more labile in the presence of flow than the L-selectin endothelial ligand, PNAd, suggesting that L-selectin ligands may have different molecular and mechanical properties. Both types of L-selectin bonds had a higher reactive compliance than P-selectin or E-selectin bonds.
白细胞在血管内皮上的捕获和滚动主要由细胞粘附受体的选择素家族介导。在平行板流动腔中，通过高速视频显微镜观察到中性粒细胞在纯化的选择素或选择素配体底物上滚动，呈现出一系列类似棘轮的步骤，并具有特征性的时间常数（卡普朗斯基，G.，C. 法尔纳里尔，O. 蒂索，A. 皮埃尔，A.-M. 贝诺利埃尔，M. C. 阿莱西，S. 卡普朗斯基，和 P. 邦格兰德。1993.《生物物理杂志》。64:1922 - 1933；阿隆，R.，D. A. 哈默，和 T. A. 斯普林格。1995.《自然》（伦敦）。374:539 - 542）。在剪切力作用下，由于键形成事件导致的中性粒细胞停滞时间短至4毫秒。在估计的单键力范围为37至250皮牛的情况下，比较了中性粒细胞在P - 选择素、E - 选择素、L - 选择素或外周淋巴结地址素（PNAd）上系留的暂停时间分布。选择素介导的暂停时间分布拟合为一阶指数函数，得出各个选择素的分子解离常数（k(off)）作为力的函数。在估计的125皮牛及以下的单键力下，所有三种选择素解离常数均等效地符合力驱动键断裂的贝尔模型和胡克弹簧模型。基于贝尔模型的无应力k(off)值对于P - 选择素、E - 选择素、L - 选择素和PNAd分别为2.4、2.6、2.8、3.8 s(-1)。P - 选择素、E - 选择素、L - 选择素和PNAd的键分离距离（反应性顺应性）分别为0.39、0.18、1.11、0.59埃。在单键力高于125皮牛时，L - 选择素和P - 选择素的解离常数远低于贝尔模型或胡克弹簧模型的预测值，这表明存在两种反应性顺应性状态。此外，在有流动的情况下，L - 选择素与其白细胞配体之间的相互作用比L - 选择素内皮配体PNAd更不稳定，这表明L - 选择素配体可能具有不同的分子和机械特性。两种类型的L - 选择素键都比P - 选择素或E - 选择素键具有更高的反应性顺应性。
