Severely impaired neuromuscular synaptic transmission causes muscle weakness in the Cacna1a-mutant mouse rolling Nagoya
Severely impaired neuromuscular synaptic transmission causes muscle weakness in the Cacna1a-mutant mouse rolling Nagoya
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DOI：
10.1111/j.1460-9568.2007.05438.x
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发表时间：
2007-04-01
影响因子：
3.4
通讯作者：
Plomp, Jaap J.
中科院分区：
文献类型：
--
作者：
Kaja, Simon;van de Ven, Rob C. G.;Plomp, Jaap J.
共济失调小鼠rolling名古屋（RN）在Cacna 1a基因中携带错义突变，该基因编码神经元Ca（v）2.1（P/Q型）Ca 2+通道的成孔亚基。Ca（v）2.1通道除了是小脑中主要的Ca-v通道类型外，还介导周围神经肌肉接头（NMJ）处的乙酰胆碱（ACh）释放。因此，RN突变诱导的Ca（v）2.1功能障碍可能会干扰NMJ的ACh释放。功能障碍可能类似于Lambert-Eaton肌无力综合征（LEMS）的情况，其中自身抗体靶向NMJ处的Ca（v）2.1通道，诱导ACh释放严重减少并导致肌无力。我们测试了RN小鼠的神经肌肉功能，并表征了膈肌、比目鱼肌和趾短屈肌中NMJ的递质释放特性。临床肌无力和疲劳表现为重复神经刺激肌电图，握力测试和倒网格悬挂试验。肌肉收缩实验显示神经肌肉传递的安全系数受损。在离体电生理实验中，我们发现严重受损的乙酰胆碱释放。与野生型相比，RN NMJ的神经刺激诱发的递质释放降低了50-75%，解释了观察到的肌肉无力。令人惊讶的是，诱发释放的减少伴随着类似的3倍增加自发乙酰胆碱释放。这种突触表型表明RN突变对不同功能性Ca（v）2.1通道参数的复杂影响，推测激活电位的正向偏移是主要特征。总之，我们的研究表明，RN小鼠的步态异常是由于共济失调和肌无力的组合，RN模型LEMS中的NMJ功能障碍的方面。
The ataxic mouse rolling Nagoya (RN) carries a missense mutation in the Cacna1a gene, encoding the pore-forming subunit of neuronal Ca(v)2.1 (P/Q-type) Ca2+ channels. Besides being the predominant type of Ca-v channel in the cerebellum, Ca(v)2.1 channels mediate acetylcholine (ACh) release at the peripheral neuromuscular junction (NMJ). Therefore, Ca(v)2.1 dysfunction induced by the RN mutation may disturb ACh release at the NMJ. The dysfunction may resemble the situation in Lambert-Eaton myasthenic syndrome (LEMS), in which autoantibodies target Ca(v)2.1 channels at NMJs, inducing severely reduced ACh release and resulting in muscle weakness. We tested neuromuscular function of RN mice and characterized transmitter release properties at their NMJs in diaphragm, soleus and flexor digitorum brevis muscles. Clinical muscle weakness and fatigue were demonstrated using repetitive nerve-stimulation electromyography, grip strength testing and an inverted grid hanging test. Muscle contraction experiments showed a compromised safety factor of neuromuscular transmission. In ex vivo electrophysiological experiments we found severely impaired ACh release. Compared to wild-type, RN NMJs had 50-75% lower nerve stimulation-evoked transmitter release, explaining the observed muscle weakness. Surprisingly, the reduction in evoked release was accompanied by an similar to 3-fold increase in spontaneous ACh release. This synaptic phenotype suggests a complex effect of the RN mutation on different functional Ca(v)2.1 channel parameters, presumably with a positive shift in activation potential as a prevailing feature. Taken together, our studies indicate that the gait abnormality of RN mice is due to a combination of ataxia and muscle weakness and that RN models aspects of the NMJ dysfunction in LEMS.