Eddleman C S, Bittner G D, Fishman H M
Department of Physiology and Biophysics, University of Texas Medical Branch, Galveston, Texas 77555-0641, USA.
Biophys J. 2000 Oct;79(4):1883-90. doi: 10.1016/S0006-3495(00)76438-1.
After axonal severance, a barrier forms at the cut ends to rapidly restrict bulk inflow and outflow. In severed crayfish axons we used the exclusion of hydrophilic, fluorescent dye molecules of different sizes (0.6-70 kDa) and the temporal decline of ionic injury current to levels in intact axons to determine the time course (0-120 min posttransection) of barrier formation and the posttransection time at which an axolemmal ionic seal had formed, as confirmed by the recovery of resting and action potentials. Confocal images showed that the posttransection time of dye exclusion was inversely related to dye molecular size. A barrier to the smallest dye molecule formed more rapidly (<60 min) than did the barrier to ionic entry (>60 min). These data show that axolemmal sealing lacks abrupt, large changes in barrier permeability that would be expected if a seal were to form suddenly, as previously assumed. Rather, these data suggest that a barrier forms gradually and slowly by restricting the movement of molecules of progressively smaller size amid injury-induced vesicles that accumulate, interact, and form junctional complexes with each other and the axolemma at the cut end. This process eventually culminates in an axolemmal ionic seal, and is not complete until ionic injury current returns to baseline levels measured in an undamaged axon.
轴突切断后，在断端形成一个屏障，迅速限制物质的大量流入和流出。在切断的小龙虾轴突中，我们利用不同大小（0.6 - 70 kDa）的亲水性荧光染料分子的排除以及离子损伤电流随时间下降至完整轴突中的水平，来确定屏障形成的时间进程（横断后0 - 120分钟）以及轴膜离子密封形成的横断后时间，静息电位和动作电位的恢复证实了这一点。共聚焦图像显示，染料排除的横断后时间与染料分子大小呈负相关。对最小染料分子的屏障形成速度比对离子进入的屏障形成速度更快（<60分钟），而对离子进入的屏障形成速度较慢（>60分钟）。这些数据表明，轴膜密封并不像之前所假设的那样，如果密封突然形成，屏障通透性会有突然的、大幅度的变化。相反，这些数据表明，屏障是通过在损伤诱导的囊泡中逐渐限制越来越小的分子的移动而逐渐缓慢形成的，这些囊泡在断端相互聚集、相互作用并与轴膜形成连接复合体。这个过程最终导致轴膜离子密封，直到离子损伤电流恢复到在未受损轴突中测量的基线水平，这个过程才算完成。
