Zheng J, Buxbaum R E, Heidemann S R
Department of Physiology, Michigan State University, E. Lansing 48824.
J Cell Biol. 1994 Dec;127(6 Pt 2):2049-60. doi: 10.1083/jcb.127.6.2049.
Neurons were grown on plastic surfaces that were untreated, or treated with polylysine, laminin, or L1 and their growth cones were detached from their culture surface by applying known forces with calibrated glass needles. This detachment force was taken as a measure of the force of adhesion of the growth cone. We find that on all surfaces, lamellipodial growth cones require significantly greater detachment force than filopodial growth cones, but this differences is, in general, due to the greater area of lamellipodial growth cones compared to filopodial growth cones. That is, the stress (force/unit area) required for detachment was similar for growth cones of lamellipodial and filopodial morphology on all surfaces, with the exception of lamellipodial growth cones on L1-treated surfaces, which had a significantly lower stress of detachment than on other surfaces. Surprisingly, the forces required for detachment (760-3,340 mudynes) were three to 15 times greater than the typical resting axonal tension, the force exerted by advancing growth cones, or the forces of retraction previously measured by essentially the same method. Nor did we observe significant differences in detachment force among growth cones of similar morphology on different culture surfaces, with the exception of lamellipodial growth cones on L1-treated surfaces. These data argue against the differential adhesion mechanism for growth cone guidance preferences in culture. Our micromanipulations revealed that the most mechanically resistant regions of growth cone attachment were confined to quite small regions typically located at the ends of filopodia and lamellipodia. Detached growth cones remained connected to the substratum at these regions by highly elastic retraction fibers. The closeness of contact of growth cones to the substratum as revealed by interference reflection microscopy (IRM) did not correlate with our mechanical measurements of adhesion, suggesting that IRM cannot be used as a reliable estimator of growth cone adhesion.
神经元生长在未经处理、或用聚赖氨酸、层粘连蛋白或L1处理过的塑料表面上，然后用校准的玻璃针施加已知力，将其生长锥从培养表面分离。这种分离力被用作生长锥粘附力的一种度量。我们发现，在所有表面上，片状伪足生长锥所需的分离力明显大于丝状伪足生长锥，但一般来说，这种差异是由于片状伪足生长锥比丝状伪足生长锥的面积更大。也就是说，除了在L1处理过的表面上的片状伪足生长锥外，所有表面上片状伪足和丝状伪足形态的生长锥分离所需的应力（力/单位面积）是相似的，L1处理过的表面上的片状伪足生长锥的分离应力明显低于其他表面。令人惊讶的是，分离所需的力（760 - 3340微达因）比典型的静息轴突张力、前进生长锥施加的力或以前用基本相同方法测量的回缩力大三到十五倍。除了L1处理过的表面上的片状伪足生长锥外，我们也未观察到不同培养表面上形态相似的生长锥在分离力上有显著差异。这些数据反驳了培养中生长锥导向偏好的差异粘附机制。我们的显微操作显示，生长锥附着的机械抗性最强的区域局限于通常位于丝状伪足和片状伪足末端的相当小的区域。分离的生长锥通过高弹性回缩纤维在这些区域与基质保持连接。干涉反射显微镜（IRM）显示的生长锥与基质的接触紧密程度与我们对粘附的力学测量不相关，这表明IRM不能用作生长锥粘附的可靠估计器。
