Ca2+-dependent inactivation of large conductance Ca2+-activated K+ (BK) channels in rat hippocampal neurones produced by pore block from an associated particle
Ca2+-dependent inactivation of large conductance Ca2+-activated K+ (BK) channels in rat hippocampal neurones produced by pore block from an associated particle
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DOI：
10.1111/j.1469-7793.1998.721bp.x
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发表时间：
1998-05-01
影响因子：
5.5
通讯作者：
Marrion, NV
中科院分区：
文献类型：
--
作者：
Hicks, GA;Marrion, NV
1.记录从急性分离的海马CA 1切除的超过90%的由内而外的补丁的大电导钙激活的K+（BK）通道的活性。神经元的失活过程取决于至少1 μ M细胞内Ca 2+的存在。失活的特征在于从持续的高开放概率（P-o）长开放时间行为到极低P-o、短开放时间通道活性的突然告密。低P-o状态（平均P-o，0.001）包括非常短的开口（时间常数（tau），类似于0.14 ms）和罕见的较长持续时间的开口（tau，类似于3.0 ms）。通道失活发生与高度可变的时间过程被观察到之前或之后立即补丁切除，或后长达2分钟的内翻记录。失活持续而记录条件是恒定的。失活逆转膜超极化，恢复率增加进一步超极化和更高的细胞外K+。失活也逆转时，细胞内Ca 2+浓度降低到100 nM，并通过应用胰蛋白酶的内部补丁表面被永久删除。此外，通过将四乙基铵离子或Shaker（Sh）B肽应用于内膜面来干扰失活。在失活过程中，通道P-O是更大的超极化，而不是去极化电位，这部分是由于一个更大的数量较长的持续时间的开放。在较长持续时间开放期间施加的去极化电压阶跃（-40至+40 mV）仅在去极化电位下产生短持续时间事件，产生具有快速衰减（tau，类似于3.8 ms）的瞬态总体平均电流。这些数据表明，海马BK通道表现出Ca 2+依赖性失活，这是提出从相关颗粒的通道的块。失活被胰蛋白酶去除，并通过降低细胞外钾而延长，这一发现表明阻断颗粒可能作用于通道的细胞内侧。
1. Recordings of the activity of the large conductance Ca2+-activated K+ (BK) channel from over 90% of inside-out patches excised from acutely dissociated hippocampal CA 1. neurones revealed an inactivation process dependent upon the presence of at least 1 mu M intracellular Ca2+. Inactivation was characterized by a sudden snitch from sustained high open probability (P-o) long open time behaviour to extremely low P-o, short open time channel activity. The low P-o state (mean P-o, 0.001) consisted of very short openings (time constant (tau), similar to 0.14 ms) and rare longer duration openings (tau, similar to 3.0 ms).2. Channel inactivation occurred with a highly variable time course being observed either prior to or immediately upon patch excision, or after up to 2 min of inside-out recording. Inactivation persisted whilst recording conditions were constant.3. Inactivation was reversed by membrane hyperpolarization, the rate of recovery increasing with further hyperpolarization and higher extracellular K+. Inactivation was also reversed when the intracellular Ca2+ concentration was lowered to 100 nM and was permanently removed by application of trypsin to the inner patch surface. In addition, inactivation was perturbed by application of either tetraethylammonium ions or the Shaker (Sh)B peptide to the inner membrane face.4. During inactivation, channel P-o was greater at hyperpolarized rather than depolarized potentials, which was partly the result of a greater number of longer duration openings. Depolarizing voltage steps (-40 to +40 mV) applied during longer duration openings produced only short duration events at the depolarized potential, yielding a transient ensemble average current with a rapid decay (tau, similar to 3.8 ms).5. These data suggest that hippocampal BK channels exhibit a Ca2+-dependent inactivation that is proposed to result from block of the channel by an associated particle. The findings that inactivation was removed by trypsin and prolonged by decreasing extracellular potassium suggest that the blocking particle may act at the intracellular side of the channel.