Chronic hypoxia up-regulates α1H T-type channels and low-threshold catecholamine secretion in rat chromaffin cells
Chronic hypoxia up-regulates α1H T-type channels and low-threshold catecholamine secretion in rat chromaffin cells
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DOI：
10.1113/jphysiol.2007.132274
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发表时间：
2007-10-01
影响因子：
5.5
通讯作者：
Carbone, E.
中科院分区：
文献类型：
--
作者：
Carabelli, V.;Marcantoni, A.;Carbone, E.
在大鼠嗜铬细胞(RCC)中，β(1)-肾上腺素能刺激所招募的α(1H)T型通道与快速胞吐相偶联，具有与高阈值钙通道相同的钙依赖性。在这里，我们发现，RCC暴露在3%O-2中的慢性缺氧(CH)12-18小时，表达类似密度的功能性T型通道，使静止细胞去极化，并有助于低电压胞吐。慢性低氧后，大多数RCC在-50 mV时已具有T型钙通道，具有与α(1H)亚型相同的门控、药理和分子特征。慢性低氧对细胞大小和高阈值钙电流密度无影响，但可通过与铁络合剂去铁胺(DFX)过夜孵育来模拟，提示低氧诱导因子(HIF)参与其中。T型通道募集独立于PKA激活和细胞外钙离子的存在。低氧招募的T型通道在静息状态下部分开放(T型“窗口电流”)，有助于将静息电位提高到更多的正值。50mU的Ni2+阻断引起5-8 mV的超极化。与T型通道相关的分泌反应可以在轻微的细胞去极化后被检测到，要么是阶跃去极化引起的电容增加，要么是[KCl]增加引起的电流尖峰。在后一种情况下，即使用2-4 mM的KCl也能诱发出胞吐爆发，50mU的M-Ni2+可使放电频率显著降低。慢性低氧不改变棘波的形状，提示低氧招募的T型通道在低电压下增加了分泌小泡的数量，而不改变儿茶酚胺的释放机制和释放的分子的量子含量。
alpha(1H) T-type channels recruited by beta(1)-adrenergic stimulation in rat chromaffin cells (RCCs) are coupled to fast exocytosis with the same Ca2+ dependence of high-threshold Ca2+ channels. Here we show that RCCs exposed to chronic hypoxia (CH) for 12-18 h in 3% O-2 express comparable densities of functional T-type channels that depolarize the resting cells and contribute to low-voltage exocytosis. Following chronic hypoxia, most RCCs exhibited T-type Ca2+ channels already available at -50 mV with the same gating, pharmacological and molecular features as the alpha(1H) isoform. Chronic hypoxia had no effects on cell size and high-threshold Ca2+ current density and was mimicked by overnight incubation with the iron-chelating agent desferrioxamine (DFX), suggesting the involvement of hypoxia-inducible factors (HIFs). T-type channel recruitment occurred independently of PKA activation and the presence of extracellular Ca2+. Hypoxia-recruited T-type channels were partially open at rest (T-type 'window-current') and contributed to raising the resting potential to more positive values. Their block by 50 mu M Ni2+ caused a 5-8 mV hyperpolarization. The secretory response associated with T-type channels could be detected following mild cell depolarizations, either by capacitance increases induced by step depolarizations or by amperometric current spikes induced by increased [KCl]. In the latter case, exocytotic bursts could be evoked even with 2-4 mM KCl and spike frequency was drastically reduced by 50 mu M Ni2+. Chronic hypoxia did not alter the shape of spikes, suggesting that hypoxia-recruited T-type channels increase the number of secreted vesicles at low voltages, without altering the mechanism of catecholamine release and the quantal content of released molecules.