重症肌无力
骨骼肌
钠通道
神经肌肉接头
神经肌肉传递
乙酰胆碱受体
下调和上调
内分泌学
自身抗体
内科学
肌肉无力
电生理学
化学
生物
神经科学
医学
受体
抗体
免疫学
钠
生物化学
基因
有机化学
作者
Olena Butenko,Stine Marie Jensen,Yvonne E. Fillié‐Grijpma,Robyn Verpalen,Jan J.G.M. Verschuuren,Silvère M. van der Maarel,Maartje G. Huijbers,Jaap J. Plomp
摘要
Abstract Muscle‐specific kinase myasthenia gravis (MuSK MG) is caused by autoantibodies against MuSK in the neuromuscular junction (NMJ). MuSK MG patients have fluctuating, fatigable skeletal muscle weakness, in particular of bulbar muscles. Severity differs greatly between patients, in spite of comparable autoantibody levels. One explanation for inter‐patient and inter‐muscle variability in sensitivity might be variations in compensatory muscle responses. Previously, we developed a passive transfer mouse model for MuSK MG. In preliminary ex vivo experiments, we observed that muscle contraction of some mice, in particular those with milder myasthenia, had become partially insensitive to inhibition by μ‐Conotoxin‐GIIIB, a blocker of skeletal muscle Na V 1.4 voltage‐gated sodium channels. We hypothesised that changes in Na V channel expression profile, possibly co‐expression of (μ‐Conotoxin‐GIIIB insensitive) Na V 1.5 type channels, might lower the muscle fibre's firing threshold and facilitate neuromuscular synaptic transmission. To test this hypothesis, we here performed passive transfer in immuno‐compromised mice, using ‘high’, ‘intermediate’ and ‘low’ dosing regimens of purified MuSK MG patient IgG4. We compared myasthenia levels, μ‐Conotoxin‐GIIIB resistance and muscle fibre action potential characteristics and firing thresholds. High‐ and intermediate‐dosed mice showed clear, progressive myasthenia, not seen in low‐dosed animals. However, diaphragm NMJ electrophysiology demonstrated almost equal myasthenic severities amongst all regimens. Nonetheless, low‐dosed mouse diaphragms showed a much higher degree of μ‐Conotoxin‐GIIIB resistance. This was not explained by upregulation of Scn5a (the Na V 1.5 gene), lowered muscle fibre firing thresholds or histologically detectable upregulated Na V 1.5 channels. It remains to be established which factors are responsible for the observed μ‐Conotoxin‐GIIIB insensitivity and whether the Na V repertoire change is compensatory beneficial or a bystander effect.
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