Schulien Anthony J, Justice Jason A, Di Maio Roberto, Wills Zachary P, Shah Niyathi H, Aizenman Elias
Department of Neurobiology.
Pittsburgh Institute for Neurodegenerative Diseases, University of Pittsburgh School of Medicine, PA, USA.
J Physiol. 2016 May 15;594(10):2647-59. doi: 10.1113/JP272117.
Increases in intracellular Zn(2+) concentrations are an early, necessary signal for the modulation of Kv2.1 K(+) channel localization and physiological function. Intracellular Zn(2+) -mediated Kv2.1 channel modulation is dependent on calcineurin, a Ca(2+) -activated phosphatase. We show that intracellular Zn(2+) induces a significant increase in ryanodine receptor-dependent cytosolic Ca(2+) transients, which leads to a calcineurin-dependent redistribution of Kv2.1 channels from pre-existing membrane clusters to diffuse localization. As such, the link between Zn(2+) and Ca(2+) signalling in this Kv2.1 modulatory pathway is established. We observe that a sublethal ischaemic preconditioning insult also leads to Kv2.1 redistribution in a ryanodine receptor-dependent fashion. We suggest that Zn(2+) may be an early and ubiquitous signalling molecule mediating Ca(2+) release from the cortical endoplasmic reticulum via ryanodine receptor activation.
Sublethal injurious stimuli in neurons induce transient increases in free intracellular Zn(2+) that are associated with regulating adaptive responses to subsequent lethal injury, including alterations in the function and localization of the delayed-rectifier potassium channel, Kv2.1. However, the link between intracellular Zn(2+) signalling and the observed changes in Kv2.1 remain undefined. In the present study, utilizing exogenous Zn(2+) treatment, along with a selective Zn(2+) ionophore, we show that transient elevations in intracellular Zn(2+) concentrations are sufficient to induce calcineurin-dependent Kv2.1 channel dispersal in rat cortical neurons in vitro, which is accompanied by a relatively small but significant hyperpolarizing shift in the voltage-gated activation kinetics of the channel. Critically, using a molecularly encoded calcium sensor, we found that the calcineurin-dependent changes in Kv2.1 probably occur as a result of Zn(2+) -induced cytosolic Ca(2+) release via activation of neuronal ryanodine receptors. Finally, we couple this mechanism with an established model for in vitro ischaemic preconditioning and show that Kv2.1 channel modulation in this process is also ryanodine receptor-sensitive. Our results strongly suggest that intracellular Zn(2+) -initiated signalling may represent an early and possibly widespread component of Ca(2+) -dependent processes in neurons.
细胞内锌离子（Zn(2+)）浓度升高是调节Kv2.1钾通道定位和生理功能的早期必要信号。细胞内锌离子介导的Kv2.1通道调节依赖于钙调神经磷酸酶，一种钙（Ca(2+)）激活的磷酸酶。我们发现细胞内锌离子会导致兰尼碱受体依赖性的胞质钙瞬变显著增加，这会导致Kv2.1通道从预先存在的膜簇向弥散定位进行钙调神经磷酸酶依赖性的重新分布。因此，在这个Kv2.1调节途径中锌离子与钙信号之间的联系得以确立。我们观察到亚致死性缺血预处理损伤也会以兰尼碱受体依赖性方式导致Kv2.1重新分布。我们认为锌离子可能是一种早期且普遍存在的信号分子，通过激活兰尼碱受体介导从皮质内质网释放钙。
神经元中的亚致死性损伤刺激会导致细胞内游离锌离子（Zn(2+)）短暂增加，这与调节对后续致死性损伤的适应性反应有关，包括延迟整流钾通道Kv2.1的功能和定位改变。然而，细胞内锌离子信号与观察到的Kv2.1变化之间的联系仍不明确。在本研究中，利用外源性锌离子处理以及一种选择性锌离子载体，我们表明细胞内锌离子浓度的短暂升高足以在体外诱导大鼠皮质神经元中钙调神经磷酸酶依赖性的Kv2.1通道分散，同时通道的电压门控激活动力学发生相对较小但显著的超极化偏移。至关重要的是，使用分子编码钙传感器，我们发现Kv2.1中钙调神经磷酸酶依赖性变化可能是由于锌离子通过激活神经元兰尼碱受体诱导胞质钙释放所致。最后，我们将此机制与已建立的体外缺血预处理模型相结合，表明该过程中Kv2.1通道调节对兰尼碱受体也敏感。我们的结果强烈表明，细胞内锌离子引发的信号可能代表神经元中钙依赖性过程的早期且可能广泛存在的组成部分。
