Many neurons including vasopressin (VP) magnocellular neurosecretory cells (MNCs) of the hypothalamic supraoptic nucleus (SON) generate afterhyperpolarizations (AHPs) during spiking to slow firing, a phenomenon known as spike frequency adaptation. The AHP is underlain by Ca²⁺-activated K⁺ currents, and while slow component (sAHP) features are well described, its mechanism remains poorly understood. Previous work demonstrated that Ca²⁺ influx through N-type Ca²⁺ channels is a primary source of sAHP activation in SON oxytocin neurons, but no obvious channel coupling was described for VP neurons. Given this, we tested the possibility of an intracellular source of sAHP activation, namely, the Ca²⁺-handling organelles endoplasmic reticulum (ER) and mitochondria in male and female Wistar rats. We demonstrate that ER Ca²⁺ depletion greatly inhibits sAHPs without a corresponding decrease in Ca²⁺ signal. Caffeine sensitized AHP activation by Ca²⁺. In contrast to ER, disabling mitochondria with CCCP or blocking mitochondria Ca²⁺ uniporters (MCUs) enhanced sAHP amplitude and duration, implicating mitochondria as a vital buffer for sAHP-activating Ca²⁺. Block of mitochondria Na⁺-dependent Ca²⁺ release via triphenylphosphonium (TPP⁺) failed to affect sAHPs, indicating that mitochondria Ca²⁺ does not contribute to sAHP activation. Together, our results suggests that ER Ca²⁺-induced Ca²⁺ release activates sAHPs and mitochondria shape the spatiotemporal trajectory of the sAHP via Ca²⁺ buffering in VP neurons. Overall, this implicates organelle Ca²⁺, and specifically ER–mitochondria-associated membrane contacts, as an important site of Ca²⁺ microdomain activity that regulates sAHP signaling pathways. Thus, this site plays a major role in influencing VP firing activity and systemic hormonal release.

许多神经元，包括下丘脑视上核 (SON) 的加压素 (VP) 大细胞神经分泌细胞 (MNC)，在尖峰放电至缓慢放电期间产生后超极化 (AHP)，这种现象称为尖峰频率适应。 AHP 的基础是 Ca ²⁺激活的 K ⁺电流，虽然慢分量 (sAHP) 特征已得到很好的描述，但其机制仍知之甚少。先前的工作表明，通过N型Ca ²⁺通道的Ca ²⁺流入是SON催产素神经元中sAHP激活的主要来源，但对于VP神经元没有描述明显的通道耦合。鉴于此，我们在雄性和雌性 Wistar 大鼠中测试了 sAHP 激活的细胞内来源的可能性，即 Ca ²⁺处理细胞器内质网 (ER) 和线粒体。我们证明，ER Ca ²⁺耗竭会极大地抑制 sAHP，而 Ca ²⁺信号不会相应降低。咖啡因使 Ca ²⁺的 AHP 激活变得敏感。与 ER 相比，用 CCCP 禁用线粒体或阻断线粒体 Ca ²⁺单向转运蛋白 (MCU) 可增强 sAHP 幅度和持续时间，这表明线粒体是 sAHP 激活 Ca ²⁺的重要缓冲液。通过三苯基膦 (TPP ⁺ ) 阻断线粒体 Na ⁺依赖性 Ca ²⁺释放未能影响 sAHP，表明线粒体 Ca ²⁺对 sAHP 激活没有贡献。总之，我们的结果表明，ER Ca ²⁺诱导的 Ca ²⁺释放激活 sAHP，线粒体通过 VP 神经元中的 Ca ²⁺缓冲塑造 sAHP 的时空轨迹。 总体而言，这表明细胞器 Ca ²⁺ ，特别是内质网线粒体相关膜接触，是调节 sAHP 信号通路的 Ca ²⁺微域活性的重要位点。因此，该位点在影响 VP 放电活动和全身激素释放方面发挥着重要作用。