面肌和骨骼肌对肌松药敏感性差异的机制及受损后发生的改变

Muscle relaxant is one of the most important ingredients in general anesthesia to ensure the absolute immobility of the patient, while the influence of muscle relaxants on facial nerve evoked electromyographic (EEMG) monitoring limits their usage in the related surgeries. Therefore, there is important significance to investigate the way to selectively reduce the influence of muscle relaxants on facial neuromuscular transmission while keep the limb skeletal muscle relaxing. Our previous research indicated that differences in sensitivities to muscle relaxants existed between facial-nerve-innervated muscles and somatic-nerve-innervated muscles, which might be related to the affinity of acetylcholine receptors (AChR) to muscle relaxant, the destity of AChR at end-plates, and the presynaptic quantal release of acetylcholine, and the later two factors were altered when the facial nerve had been injured. The current research is designed to investigate the hypothesis as follows: First, whether the different affinity of AChR at end-plates to muscle rlaxants between the facial-nerve-innervated muscles and somatic-nerve-innervated muscles is related to the different composition of AChR subunits. Second, whether the changes in EEMG responses in facial nerves under different extents of injuries is related to the composition of AChR subunits and the character of their expressions. Finally, whether the sensitization of the inhibition on acetylcholine release in injured facial nerves by muscle relaxants is mediated by the changes of the patterns of presynaptic acetylcholine release. The results of the study are of significant importance to determine a proper strategy for rational usage of muscle relaxants in general anesthesia for the surgeries requiring EEMG monitoring.

肌松药是全麻方案中确保患者绝对制动的重要组成部分，然而肌松药对面神经诱发肌电位（EEMG）监测的影响限制了它们在面神经相关手术中的应用。因此，研究如何选择性减少肌松药对面神经-肌肉神经信号传导的影响，而保留肌松药对四肢骨骼肌的肌肉松弛作用具有重要的意义。我们前期研究发现：面肌和肢体骨骼肌对肌松药敏感性存在差异，造成这种差异的机制包括肌肉终板区乙酰胆碱受体（AChR）对肌松药亲和力、AChR密度以及突触前膜乙酰胆碱释放的差异,并且在受损时后两者也发生了改变。本项目拟进一步研究面肌和骨骼肌AChR对肌松药亲和力的差异是否与AChR亚基构成比相关；不同损伤程度面神经支配的肌肉AChR亚基构成比、表达特征与其EEMG反应的关系；受损面神经突触前膜乙酰胆碱释放机制的改变是否介导了肌松药对乙酰胆碱释放抑制的敏化。本项目对临床上实施面神经监测的手术中肌松药的合理使用具有重要的意义。

术中面神经诱发肌电位（EEMG）监测是避免医源性面神经损伤的重要手段，全麻方案必要成分的肌松药是影响面神经监测的关键因素。因此，研究如何选择性减少肌松药对面神经-肌肉神经信号传导的影响，而保留肌松药对四肢骨骼肌的肌肉松弛作用具有重要的意义。. 我们的研究证明，受损面神经支配的口轮匝肌的诱发肌电位（EEMG）反应与面神经受损程度呈负相关，面神经损伤越严重，所支配肌肉的EEMG反应越减弱。采用离体药效学研究证实，正常口轮匝肌罗库溴铵IC50大于腓肠肌，提示两种肌肉对罗库溴铵的敏感性不同，面神经受损后，口轮匝肌罗库溴铵IC50增加，并随观察时间呈动态变化。受损面神经的突触前膜ACh量子式释放数目与神经损伤程度也呈负相关，提示神经损伤导致的ACh量子式释放减少可能成为所支配肌肉EEMG反应减弱的原因之一。采用RT-PCR和Western blot检测证实，面神经受损后，其突触后膜a1、β1、δ和ε各亚基表达均增加，并出现胚胎型γ亚基大量表达，所有亚基表达量均与损伤程度呈正相关，而且随时间呈动态变化。提示这种亚基表达构成比的变化可能造成对乙酰胆碱的亲和力改变，从而导致相对应肌肉EEMG反应减弱。采用免疫荧光染色证实，面神经受损后，不仅口轮匝肌运动终板处a1、β1、δ和ε各亚基表达均增加并出现胚胎型γ亚基大量表达，同时增加的亚基也表达于终板外区的肌纤维膜上，这种亚基构成比和亚基空间位置的变化可能造成对乙酰胆碱的结合率改变，导致相对应肌肉EEMG反应减弱。采用RT-PCR检测证实，面神经受损后，口轮匝肌肌源性调节因子Myogenin和MRF4的表达增加，表达量与损伤程度呈正相关，并随观察时间呈动态变化。Myogenin和MRF4的表达优先或同步于乙酰胆碱受体a1亚基的表达，且损伤程度越重，Myogenin、MRF4和a1亚基的表达上调出现得越早，持续表达时间越长。. 以上研究成果已在J Surg Res和Int J Clin Exp Pathol发表两篇SCI文章，另有三篇SCI文章已完成待发表。