Barzan Ruxandra, Pfeiffer Friederike, Kukley Maria
Group of Neuron Glia Interaction, Werner Reichardt Centre for Integrative Neuroscience, University of Tübingen Tübingen, Germany.
Front Cell Neurosci. 2016 Jun 2;10:135. doi: 10.3389/fncel.2016.00135. eCollection 2016.
In the peripheral nervous system (PNS) a vast number of axons are accommodated within fiber bundles that constitute peripheral nerves. A major function of peripheral axons is to propagate action potentials along their length, and hence they are equipped with Na(+) and K(+) channels, which ensure successful generation, conduction and termination of each action potential. However little is known about Ca(2+) ion channels expressed along peripheral axons and their possible functional significance. The goal of the present study was to test whether voltage-gated Ca(2+) channels (VGCCs) are present along peripheral nerve axons in situ and mediate rapid activity-dependent Ca(2+) elevations under physiological circumstances. To address this question we used mouse sciatic nerve slices, Ca(2+) indicator Oregon Green BAPTA-1, and 2-photon Ca(2+) imaging in fast line scan mode (500 Hz). We report that transient increases in intra-axonal Ca(2+) concentration take place along peripheral nerve axons in situ when axons are stimulated electrically with single pulses. Furthermore, we show for the first time that Ca(2+) transients in peripheral nerves are fast, i.e., occur in a millisecond time-domain. Combining Ca(2+) imaging and pharmacology with specific blockers of different VGCCs subtypes we demonstrate that Ca(2+) transients in peripheral nerves are mediated mainly by N-type and L-type VGCCs. Discovery of fast Ca(2+) entry into the axonal shafts through VGCCs in peripheral nerves suggests that Ca(2+) may be involved in regulation of action potential propagation and/or properties in this system, or mediate neurotransmitter release along peripheral axons as it occurs in the optic nerve and white matter of the central nervous system (CNS).
在周围神经系统（PNS）中，大量轴突容纳在构成周围神经的纤维束内。周围轴突的一个主要功能是沿其长度传播动作电位，因此它们配备有Na(+)和K(+)通道，以确保每个动作电位的成功产生、传导和终止。然而，关于沿周围轴突表达的Ca(2+)离子通道及其可能的功能意义，人们知之甚少。本研究的目的是测试电压门控Ca(2+)通道（VGCCs）是否原位存在于周围神经轴突上，并在生理情况下介导快速的活动依赖性Ca(2+)升高。为了解决这个问题，我们使用了小鼠坐骨神经切片、Ca(2+)指示剂 Oregon Green BAPTA-1以及快速线扫描模式（500 Hz）下的双光子Ca(2+)成像技术。我们报告称，当轴突被单脉冲电刺激时，原位周围神经轴突会出现轴突内Ca(2+)浓度的短暂升高。此外，我们首次表明周围神经中的Ca(2+)瞬变很快，即在毫秒时域内发生。通过将Ca(2+)成像和药理学与不同VGCCs亚型的特异性阻滞剂相结合，我们证明周围神经中的Ca(2+)瞬变主要由N型和L型VGCCs介导。通过VGCCs快速进入周围神经轴突干的Ca(2+)的发现表明，Ca(2+)可能参与该系统中动作电位传播和/或特性的调节，或者像在中枢神经系统（CNS）的视神经和白质中那样介导沿周围轴突的神经递质释放。
