Neuroscience Graduate Program, University of California, San Francisco, California 94158.
Neuroscience Graduate Program, University of California, San Francisco, California 94158
J Neurosci. 2021 Apr 28;41(17):3764-3776. doi: 10.1523/JNEUROSCI.2843-20.2021. Epub 2021 Mar 17.
The axon initial segment (AIS) is a specialized neuronal compartment in which synaptic input is converted into action potential (AP) output. This process is supported by a diverse complement of sodium, potassium, and calcium channels (Ca). Different classes of sodium and potassium channels are scaffolded at specific sites within the AIS, conferring unique functions, but how calcium channels are functionally distributed within the AIS is unclear. Here, we use conventional two-photon laser scanning and diffraction-limited, high-speed spot two-photon imaging to resolve AP-evoked calcium dynamics in the AIS with high spatiotemporal resolution. In mouse layer 5 prefrontal pyramidal neurons, calcium influx was mediated by a mix of Ca2 and Ca3 channels that differentially localized to discrete regions. Ca3 functionally localized to produce nanodomain hotspots of calcium influx that coupled to ryanodine-sensitive stores, whereas Ca2 localized to non-hotspot regions. Thus, different pools of Cas appear to play distinct roles in AIS function. The axon initial segment (AIS) is the site where synaptic input is transformed into action potential (AP) output. It achieves this function through a diverse complement of sodium, potassium, and calcium channels (Ca). While the localization and function of sodium channels and potassium channels at the AIS is well described, less is known about the functional distribution of Cas. We used high-speed two-photon imaging to understand activity-dependent calcium dynamics in the AIS of mouse neocortical pyramidal neurons. Surprisingly, we found that calcium influx occurred in two distinct domains: Ca3 generates hotspot regions of calcium influx coupled to calcium stores, whereas Ca2 channels underlie diffuse calcium influx between hotspots. Therefore, different Ca classes localize to distinct AIS subdomains, possibly regulating distinct cellular processes.
轴突起始段 (AIS) 是一种特殊的神经元结构，其中突触输入被转化为动作电位 (AP) 输出。这一过程由多种钠、钾和钙通道 (Ca) 支持。不同类型的钠和钾通道在 AIS 内的特定部位被支架化，赋予其独特的功能，但 Ca 通道在 AIS 内如何在功能上分布尚不清楚。在这里，我们使用传统的双光子激光扫描和衍射极限的高速点双光子成像技术，以高时空分辨率解析 AIS 中的 AP 诱发钙动力学。在小鼠皮层 5 层前额叶锥体神经元中，钙内流是由 Ca2 和 Ca3 通道混合介导的，这些通道在离散区域中具有不同的定位。Ca3 功能定位产生钙内流的纳米域热点，与ryanodine 敏感的储存器偶联，而 Ca2 定位到非热点区域。因此，不同的 Cas 池似乎在 AIS 功能中发挥不同的作用。轴突起始段 (AIS) 是将突触输入转化为动作电位 (AP) 输出的部位。它通过多种钠、钾和钙通道 (Ca) 来实现这一功能。虽然 AIS 上的钠通道和钾通道的定位和功能已经得到了很好的描述，但 Cas 的功能分布知之甚少。我们使用高速双光子成像来了解小鼠新皮层锥体神经元 AIS 中的活动依赖性钙动力学。令人惊讶的是，我们发现钙内流发生在两个不同的区域：Ca3 产生钙内流的热点区域，与钙储存偶联，而 Ca2 通道则在热点之间产生弥散的钙内流。因此，不同的 Cas 类群定位于不同的 AIS 亚区，可能调节不同的细胞过程。
