Department of Physiology, The University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, San Antonio, TX 78229, USA.
Eur J Neurosci. 2011 Sep;34(5):695-704. doi: 10.1111/j.1460-9568.2011.07799.x. Epub 2011 Aug 16.
Large-conductance voltage- and calcium-activated potassium (BK) channels are large-conductance calcium- and voltage-activated potassium channels critical for neuronal excitability. Some neurons express so called fast-gated, type I BK channels. Other neurons express BK channels assembled with the accessory β4 subunit conferring slow gating of type II BK channels. However, it is not clear how protein phosphorylation modulates these two distinct BK channel types. Using β4-knockout mice, we compared fast- or slow-gated BK channels in response to changes in phosphorylation status of hippocampus dentate gyrus granule neurons. We utilized the selective PP2A/PP4 phosphatase inhibitor Fostriecin to study changes in action potential shape and firing properties of the neurons. In β4-knockout neurons, Fostriecin increases BK current, speeds up BK channel activation and reduces action potential amplitudes. Fostriecin increases spiking during early components of an action potential train. In contrast, inhibition of BK channels through β4 in wild-type neurons or by the BK channel inhibitor Paxilline opposes Fostriecin effects. Voltage clamp recordings of neurons reveal that Fostriecin increases both calcium and BK currents. However, Fostriecin does not activate BK α channels in transfected HEK293 cells lacking calcium channels. In summary, these results suggest that fast-gating, type I BK channels lacking β4 can increase neuronal excitability in response to reduced phosphatase activity and activation of calcium channels. By opposing BK channel activation, the β4 subunit plays an important role in moderating firing frequency regardless of changes in phosphorylation status.
大电导电压和钙激活钾（BK）通道是神经元兴奋性的关键大电导钙和电压激活钾通道。一些神经元表达所谓的快速门控、I 型 BK 通道。其他神经元表达与辅助β4 亚基组装的 BK 通道，赋予 II 型 BK 通道的缓慢门控。然而，目前尚不清楚蛋白磷酸化如何调节这两种不同的 BK 通道类型。使用β4 敲除小鼠，我们比较了海马齿状回颗粒神经元磷酸化状态变化时的快速或慢速门控 BK 通道。我们利用选择性 PP2A/PP4 磷酸酶抑制剂 Fostriecin 研究神经元动作电位形状和放电特性的变化。在β4 敲除神经元中，Fostriecin 增加 BK 电流，加速 BK 通道激活并降低动作电位幅度。Fostriecin 在动作电位序列的早期成分中增加了尖峰。相比之下，在野生型神经元中通过β4 抑制 BK 通道或通过 BK 通道抑制剂 Paxilline 拮抗 Fostriecin 的作用。神经元的电压钳记录显示，Fostriecin 增加钙和 BK 电流。然而，在缺乏钙通道的转染 HEK293 细胞中，Fostriecin 不会激活 BKα 通道。总之，这些结果表明，缺乏β4 的快速门控、I 型 BK 通道可以增加神经元兴奋性，以响应磷酸酶活性降低和钙通道激活。通过拮抗 BK 通道激活，β4 亚基在调节放电频率方面发挥重要作用，而与磷酸化状态的变化无关。
