PDF(Pubmed)
Abstract：
The toxin AaH-II, from the scorpion Androctonus australis Hector venom, is a 64 amino acid peptide that targets voltage-gated Na+ channels (VGNCs) and slows their inactivation. While at macroscopic cellular level AaH-II prolongs the action potential (AP), a functional analysis of the effect of the toxin in the axon initial segment (AIS), where VGNCs are highly expressed, was never performed so far. Here, we report an original analysis of the effect of AaH-II on the AP generation in the AIS of neocortical layer-5 pyramidal neurons from mouse brain slices. After determining that AaH-II does not discriminate between Nav1.2 and Nav1.6, i.e. between the two VGNC isoforms expressed in this neuron, we established that 7 nM was the smallest toxin concentration producing a minimal detectable deformation of the somatic AP after local delivery of the toxin. Using membrane potential imaging, we found that, at this minimal concentration, AaH-II substantially widened the AP in the AIS. Using ultrafast Na+ imaging, we found that local application of 7 nM AaH-II caused a large increase in the slower component of the Na+ influx in the AIS. Finally, using ultrafast Ca2+ imaging, we observed that 7 nM AaH-II produces a spurious slow Ca2+ influx via Ca2+-permeable VGNCs. Molecules targeting VGNCs, including peptides, are proposed as potential therapeutic tools. Thus, the present analysis in the AIS can be considered a general proof-of-principle on how high-resolution imaging techniques can disclose drug effects that cannot be observed when tested at the macroscopic level.
摘要：
毒素AaH-II,蝎子AndroctonusaustralisHector毒液，是一种64个氨基酸的肽,其靶向电压门控Na+通道(VGNC)并减缓其失活。虽然在宏观细胞水平AaH-II延长动作电位（AP），对毒素在轴突初始片段（AIS）中的作用进行功能分析，VGNC高度表达，到目前为止从未表演过。这里,我们报告了AaH-II对小鼠脑片新皮层5锥体神经元AIS中AP生成的影响的原始分析。在确定AaH-II不区分Nav1.2和Nav1.6之后，即在该神经元中表达的两个VGNC同工型之间，我们确定7nM是最小的毒素浓度,在局部递送毒素后产生最小的可检测的体细胞AP变形。使用膜电位成像，我们发现,在这个最低浓度下，AaH-II大幅扩大了AIS中的AP。使用超快Na+成像，我们发现，局部应用7nMAaH-II会导致AIS中Na内流的较慢成分大量增加。最后,使用超快Ca2+成像，我们观察到7nMAaH-II通过可透Ca2+的VGNC产生虚假的缓慢Ca2+流入。靶向VGNC的分子，包括肽，被提议作为潜在的治疗工具。因此，AIS中的当前分析可以被认为是高分辨率成像技术如何揭示在宏观水平上无法观察到的药物作用的一般原理证明.
