Low pHo boosts burst firing and catecholamine release by blocking TASK-1 and BK channels while preserving Cav1 channels in mouse chromaffin cells
Low pHo boosts burst firing and catecholamine release by blocking TASK-1 and BK channels while preserving Cav1 channels in mouse chromaffin cells
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DOI：
10.1113/jp273735
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发表时间：
2017-04-15
影响因子：
5.5
通讯作者：
Carbone, Emilio
中科院分区：
文献类型：
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作者：
Guarina, Laura;Vandael, David H. F.;Carbone, Emilio
小鼠染色质细胞（mcc）产生动作电位（AP）放电，调节Ca2+依赖性儿茶酚胺（CAs）的释放。最近的研究结果表明，mcc具有多种自发放电模式，从常见的“音调不规则”到不太频繁的“突发”放电。后者在一小部分mcc中很明显，但当Nav1.3/1.7通道可用性降低或负责BK通道失活的Slo1 β 2亚基被删除时，通常会发生这种情况。突发放电导致Ca2+进入大量增加，并使CA释放增强约3.5倍，因此可能是调节mcc功能的关键机制。为了揭示爆发的生理作用，我们研究了酸中毒对mcc活性的影响。将细胞外pH值（pHo）从7.4降低到7.0和6.6，可诱导10- 15mv的细胞去极化，并产生重复的脉冲。pHo 6.6下的脉冲持续时间约为330 ms，发生频率为1 ~ 2 Hz，导致CA累积释放增加7倍。突发放电源于ph敏感的TASK-1/TASK-3通道受到抑制，以及pHo 7.0时BK通道电导降低40%。同样的pHo对mcc中支持AP发射的Nav、Cav、Kv和SK通道几乎没有影响。TASK-1阻滞剂A1899 （300 nM）和BK阻滞剂paxilline （300 nM）的混合物可以模拟pHo 6.6的爆发，并且可以通过添加3 μ M硝苯地平阻断l型通道来阻止。这两种阻滞剂的混合物使ca的累积分泌量比低ph时增加了12倍，这表明质子对囊泡释放的作用主要是离子电导变化的结果，离子电导变化增加了爆发时eca（2+）的进入。我们的数据提供了直接证据，表明mcc对低pHo的反应是持续去极化、爆发放电和ca分泌增强，从而模仿了cc对剧烈运动和肌肉疲劳时产生的急性酸中毒和高钾血症的生理反应。
Mouse chromaffin cells (MCCs) generate action potential (AP) firing that regulates the Ca2+-dependent release of catecholamines (CAs). Recent findings indicate that MCCs possess a variety of spontaneous firing modes that span from the common `tonic-irregular' to the less frequent `burst' firing. This latter is evident in a small fraction of MCCs but occurs regularly when Nav1.3/1.7 channels aremade less available or when the Slo1 beta 2-subunit responsible for BK channel inactivation is deleted. Burst firing causes large increases of Ca2+-entry and potentiates CA release by similar to 3.5-fold and thusmay be a key mechanism for regulatingMCCfunction. With the aim to uncover a physiological role for burst-firing we investigated the effects of acidosis onMCC activity. Lowering the extracellular pH(pHo) from7.4 to 7.0 and 6.6 induces cell depolarizations of 10-15mVthat generate repeated bursts. Bursts at pHo 6.6 lasted similar to 330 ms, occurred at 1-2 Hz and caused an similar to 7-fold increase of CA cumulative release. Burst firing originates fromthe inhibition of the pH-sensitive TASK-1/TASK-3 channels and from a 40% BK channel conductance reduction at pHo 7.0. The same pHo had little or no effect on Nav, Cav, Kv and SK channels that support AP firing in MCCs. Burst firing of pHo 6.6 could be mimicked by mixtures of the TASK-1 blocker A1899 (300 nM) and BK blocker paxilline (300 nM) and could be prevented by blocking L-type channels by adding 3 mu M nifedipine. Mixtures of the two blockers raised cumulative CA-secretion even more than lowpHo (similar to 12-fold), showing that the action of protons on vesicle release is mainly a result of the ionic conductance changes that increaseCa(2+)-entry during bursts. Our data provide direct evidence suggesting that MCCs respond to low pHo with sustained depolarization, burst firing and enhanced CA-secretion, thus mimicking the physiological response of CCs to acute acidosis and hyperkalaemia generated during heavy exercise and muscle fatigue.