Ligand-Gating by Ca2+ Is Rate Limiting for Physiological Operation of BKCa Channels
Ligand-Gating by Ca2+ Is Rate Limiting for Physiological Operation of BKCa Channels
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DOI：
10.1523/jneurosci.5443-12.2013
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发表时间：
2013-04-24
影响因子：
5.3
通讯作者：
Fakler, Bernd
中科院分区：
文献类型：
--
作者：
Berkefeld, Henrike;Fakler, Bernd
大电导钙离子和电压激活钾通道（BKCa）塑造神经元兴奋性和信号转导。这反映了跨膜电压和细胞内钙浓度（[Ca 2 +]（i））的综合影响，门控通道。这种双门控主要被研究为通过定义的稳态[Ca 2 +]（i）调制的电压触发门控，这是一种不接近天然条件的范例。在这里，我们使用亚毫秒的变化[Ca 2 +]（i），以研究在不同的膜电位在生理范围内的中国仓鼠卵巢细胞中表达的BKCa通道的Ca 2+触发门控的时间过程。结果表明，Ca 2+可以有效地门控BKCa通道，并且Ca 2+门控与电压驱动的门控有很大不同。最突出的是，Ca 2+门控显示出在Ca 2+应用和通道开放之间的毫秒范围内的显著延迟（开始前延迟），并且在整个[Ca 2 +]（i）-电压平面上表现出较慢的动力学。这两种特征都被共同组装的BK β 4或导致癫痫的突变选择性地改变，分别减缓失活或加速激活并减少发作前延迟。类似地，与电压激活的Ca 2+（Cav）通道的BKCa通道的共组装，反映了天然配置，将发作前延迟降低至亚毫秒值。在BKCa-Cav复合物中，超极化K+电流响应的时间过程由BKCa通道的Ca 2+门控决定。与Cav-mediated Ca 2+内流一致，门控在超极化电位下最快，但随着膜电位的去极化而降低。我们的研究结果表明，在实验范例意味着近似的生理条件下，BKCa通道主要作为配体激活的通道，由细胞内Ca 2+门控和Ca 2+门控调谐为快速响应神经元BKCa-Cav复合物。
Large conductance Ca2+- and voltage-activated potassium channels (BKCa) shape neuronal excitability and signal transduction. This reflects the integrated influences of transmembrane voltage and intracellular calcium concentration ([Ca2+](i)) that gate the channels. This dual gating has been mainly studied as voltage-triggered gating modulated by defined steady-state [Ca2+](i), a paradigm that does not approximate native conditions. Here we use submillisecond changes of [Ca2+](i) to investigate the time course of the Ca2+-triggered gating of BKCa channels expressed in Chinese hamster ovary cells at distinct membrane potentials in the physiological range. The results show that Ca2+ can effectively gate BKCa channels and that Ca2+ gating is largely different from voltage-driven gating. Most prominently, Ca2+ gating displays a pronounced delay in the millisecond range between Ca2+ application and channel opening (pre-onset delay) and exhibits slower kinetics across the entire [Ca2+](i)-voltage plane. Both characteristics are selectively altered by co-assembled BK beta 4 or an epilepsy-causing mutation that either slows deactivation or speeds activation and reduces the pre-onset delay, respectively. Similarly, co-assembly of the BKCa channels with voltage-activated Ca2+ (Cav) channels, mirroring the native configuration, decreased the pre-onset delay to submillisecond values. In BKCa-Cav complexes, the time course of the hyperpolarizing K+-current response is dictated by the Ca2+ gating of the BKCa channels. Consistent with Cav-mediated Ca2+ influx, gating was fastest at hyperpolarized potentials, but decreased with depolarization of the membrane potential. Our results demonstrate that under experimental paradigms meant to approximate the physiological conditions BKCa channels primarily operate as ligand-activated channels gated by intracellular Ca2+ and that Ca2+ gating is tuned for fast responses in neuronal BKCa-Cav complexes.