The human adult subtype ACh receptor channel has high Ca2+ permeability and predisposes to endplate Ca2+ overloading
The human adult subtype ACh receptor channel has high Ca2+ permeability and predisposes to endplate Ca2+ overloading
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DOI：
10.1113/jphysiol.2006.108092
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发表时间：
2006-05-15
影响因子：
5.5
通讯作者：
Engel, Andrew G.
中科院分区：
文献类型：
--
作者：
Fucile, Sergio;Sucapane, Antonietta;Engel, Andrew G.
慢通道先天性肌无力综合征，由终板乙酰胆碱受体（AChR）亚基突变引起，导致突触电流延长和Ca2+超载对突触后区域的兴奋性毒性损伤。Ca2+超载可能完全是由于AChR通道的开放时间延长，或者可能是由突变通道的Ca2+通透性增强引起的。因此，我们测量了含有α G153S或α V249F慢通道突变的achr和P-f尚未确定的野生型人类achr的分数Ca2+电流，定义为Ca2+离子携带的总ach诱发电流（P-f）的百分比。实验在瞬时转染的GH4C1细胞和人肌管中进行，同时记录ach诱发的全细胞电流和fura-2荧光信号。我们发现野生型人终板AChR的P-f异常高（P-f接近7%），但α V249F和α G153S突变均未改变P-f。含有野生型或突变α亚基的胎儿人achr的P-f要低得多（2-3%）。我们得出结论，人类终板AChR的Ca2+通透性高于其他任何人类尼古丁AChR，除了含有α 7的AChR (p - f> 10%)；α G153S和α V249F突变均不影响胎儿或成人终板achr的P-f。然而，当AChR通道的打开事件被改变的AChR通道动力学延长时，人类AChR固有的高Ca2+通透性可能易导致终板肌病的发展。
Slow-channel congenital myasthenic syndrome, caused by mutations in subunits of the endplate ACh receptor (AChR), results in prolonged synaptic currents and excitotoxic injury of the postsynaptic region by Ca2+ overloading. The Ca2+ overloading could be due entirely to the prolonged openings of the AChR channel or could be abetted by enhanced Ca2+ permeability of the mutant channels. We therefore measured the fractional Ca2+ current, defined as the percentage of the total ACh-evoked current carried by Ca2+ ions (P-f), for AChRs harbouring the alpha G153S or the alpha V249F slow-channel mutation, and for wild-type human AChRs in which P-f has not yet been determined. Experiments were performed in transiently transfected GH4C1 cells and human myotubes with simultaneous recording of ACh-evoked whole-cell currents and fura-2 fluorescence signals. We found that the P-f of the wild-type human endplate AChR was unexpectedly high (P-f similar to 7%), but neither the alpha V249F nor the alpha G153S mutation altered P-f. Fetal human AChRs containing either the wild-type or the mutated alpha subunit had a much lower P-f (2-3%). We conclude that the Ca2+ permeability of human endplate AChRs is higher than that reported for any other human nicotinic AChR, with the exception of alpha 7-containing AChRs (P-f > 10%); and that neither the alpha G153S nor the alpha V249F mutations affect the P-f of fetal or adult endplate AChRs. However, the intrinsically high Ca2+ permeability of human AChRs probably predisposes to development of the endplate myopathy when opening events of the AChR channel are prolonged by altered AChR-channel kinetics.