Shi R, Asano T, Vining N C, Blight A R
Division of Neurosurgery, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, USA.
J Neurophysiol. 2000 Oct;84(4):1763-9. doi: 10.1152/jn.2000.84.4.1763.
The process of sealing of damaged axons was examined in isolated strips of white matter from guinea pig spinal cord by recording the "compound membrane potential," using a sucrose-gap technique, and by examining uptake of horseradish peroxidase (HRP). Following axonal transection, exponential recovery of membrane potential occurred with a time constant of 20 +/- 5 min, at 37 degrees C, and extracellular calcium activity (Ca(2+)) of 2 mM. Most axons excluded HRP by 30 min following transection. The rate of sealing was reduced by lowering calcium and was effectively blocked at Ca(2+) </= 0.5 mM, under which condition most axons continued to take up HRP for more than 1 h. Sealing at higher Ca(2+) was blocked by calpain inhibitors (calpeptin and calpain inhibitor-1) indicating a requirement for type II (mM) calpain in the sealing process. Following compression injury, the amplitude of the maximal compound action potential conducted through the injury site was reduced. The extent of amplitude reduction was increased when the tract was superfused with calcium-free Krebs' solution (Ca(2+) replaced by Mg(2+)). These results suggest that the fall in Ca(2+) seen following injury in vivo is sufficient to prevent membrane sealing and may paradoxically contribute to axonal dieback, retrograde cell death, and "secondary" axonal disruption.
通过使用蔗糖间隙技术记录“复合膜电位”，并检测辣根过氧化物酶（HRP）的摄取情况，对豚鼠脊髓白质分离条带中受损轴突的封闭过程进行了研究。轴突横断后，在37℃、细胞外钙活性（Ca(2+)）为2 mM的条件下，膜电位呈指数恢复，时间常数为20±5分钟。大多数轴突在横断后30分钟时排斥HRP。降低钙浓度会降低封闭速率，当Ca(2+)≤0.5 mM时封闭被有效阻断，在此条件下大多数轴突会持续摄取HRP超过1小时。在较高Ca(2+)时的封闭被钙蛋白酶抑制剂（钙肽素和钙蛋白酶抑制剂-1）阻断，表明在封闭过程中需要II型（毫摩尔）钙蛋白酶。压缩损伤后，通过损伤部位传导的最大复合动作电位的幅度降低。当束状组织用无钙的克雷布斯溶液（Ca(2+)被Mg(2+)取代）灌注时，幅度降低的程度会增加。这些结果表明，体内损伤后Ca(2+)的下降足以阻止膜封闭，并且可能反常地导致轴突回缩、逆行性细胞死亡和“继发性”轴突破坏。
