Department of Physiology, University of Maryland School of Medicine, Baltimore, MD 21201, USA.
Proc Natl Acad Sci U S A. 2012 Nov 13;109(46):18997-9002. doi: 10.1073/pnas.1205573109. Epub 2012 Oct 29.
Large-conductance calcium-activated potassium channels (BK) are potent negative regulators of excitability in neurons and muscle, and increasing BK current is a novel therapeutic strategy for neuro- and cardioprotection, disorders of smooth muscle hyperactivity, and several psychiatric diseases. However, in some neurons, enhanced BK current is linked with seizures and paradoxical increases in excitability, potentially complicating the clinical use of agonists. The mechanisms that switch BK influence from inhibitory to excitatory are not well defined. Here we investigate this dichotomy using a gain-of-function subunit (BK(R207Q)) to enhance BK currents. Heterologous expression of BK(R207Q) generated currents that activated at physiologically relevant voltages in lower intracellular Ca(2+), activated faster, and deactivated slower than wild-type currents. We then used BK(R207Q) expression to broadly augment endogenous BK currents in vivo, generating a transgenic mouse from a circadian clock-controlled Period1 gene fragment (Tg-BK(R207Q)). The specific impact on excitability was assessed in neurons of the suprachiasmatic nucleus (SCN) in the hypothalamus, a cell type where BK currents regulate spontaneous firing under distinct day and night conditions that are defined by different complements of ionic currents. In the SCN, Tg-BK(R207Q) expression converted the endogenous BK current to fast-activating, while maintaining similar current-voltage properties between day and night. Alteration of BK currents in Tg-BK(R207Q) SCN neurons increased firing at night but decreased firing during the day, demonstrating that BK currents generate bidirectional effects on neuronal firing under distinct conditions.
大电导钙激活钾通道（BK）是神经元和肌肉兴奋性的有效负调节剂，增加 BK 电流是神经和心脏保护、平滑肌过度活跃障碍以及几种精神疾病的新的治疗策略。然而，在一些神经元中，增强的 BK 电流与癫痫发作和兴奋性的反常增加有关，这可能使激动剂的临床应用复杂化。将 BK 影响从抑制性转变为兴奋性的机制尚未明确。在这里，我们使用一种功能获得亚基（BK（R207Q））来增强 BK 电流，从而研究这种二分法。异源表达的 BK（R207Q）产生的电流在生理相关的电压下在较低的细胞内 Ca2+中激活，比野生型电流更快地激活和更缓慢地失活。然后，我们使用 BK（R207Q）表达在体内广泛增强内源性 BK 电流，从生物钟控制的 Period1 基因片段（Tg-BK（R207Q））生成转基因小鼠。兴奋性的特定影响在下丘脑视交叉上核（SCN）的神经元中进行评估，BK 电流在昼夜不同条件下调节自发性放电，而这些条件是由不同的离子电流组成定义的。在 SCN 中，Tg-BK（R207Q）表达将内源性 BK 电流转换为快速激活，同时保持昼夜之间相似的电流-电压特性。Tg-BK（R207Q）SCN 神经元中 BK 电流的改变增加了夜间的放电，但减少了白天的放电，表明在不同条件下，BK 电流对神经元放电产生双向影响。
