Intracellular Mg2+ is a voltage-dependent pore blocker of HCN channels.
Intracellular Mg2+ is a voltage-dependent pore blocker of HCN channels.
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细胞内 Mg2 是 HCN 通道的电压依赖性孔阻断剂。
DOI：
10.1152/ajpcell.00154.2008
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发表时间：
2008
期刊：
影响因子：
--
通讯作者：
Larsson,HPeter
中科院分区：
文献类型：
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作者：
Vemana,Sriharsha;Pandey,Shilpi;Larsson,HPeter
超极化激活的环核苷酸门控 (HCN) 通道由膜超极化激活，膜超极化产生时间依赖性内向整流电流，由内在电压传感器 S4 的运动门控。然而，HCN 电流的内向整流不仅在时间相关的 HCN 电流中观察到，而且在瞬时 HCN 尾电流中也观察到。内向整流也可以在主要具有与时间无关的电流的突变型 HCN 通道中看到。在本研究中，我们表明细胞内 Mg2+ 作为 HCN 通道的电压依赖性阻断剂发挥作用，起到减少外向电流的作用。 HCN 通道对 Mg2+ 的亲和力处于生理范围内，+50 mV 时，Mg2+ 结合的 IC50 在 HCN2 通道中为 0.53 mM，在 HCN1 通道中为 0.82 mM。 HCN1 通道的 Mg2+ 结合位点的有效电距离为 0.19，表明结合位点位于孔中。去除 HCN1 通道选择性过滤器中的半胱氨酸会降低对 Mg2+ 的亲和力，表明该残留物形成孔内深处结合位点的一部分。我们的结果表明 Mg2+ 充当电压依赖性孔阻滞剂，因此减少通过 HCN 通道的外向电流。 Mg2+的孔阻塞作用可能发挥重要的生理作用，特别是对于缓慢门控的HCN2和HCN4通道。 Mg2+ 可能会阻止动作电位平台处的向外超极化 HCN 电流，从而防止动作电位过早终止。
Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels are activated by membrane hyperpolarization that creates time-dependent, inward rectifying currents, gated by the movement of the intrinsic voltage sensor S4. However, inward rectification of the HCN currents is not only observed in the time-dependent HCN currents, but also in the instantaneous HCN tail currents. Inward rectification can also be seen in mutant HCN channels that have mainly time-independent currents . In the present study, we show that intracellular Mg2+functions as a voltage-dependent blocker of HCN channels, acting to reduce the outward currents. The affinity of HCN channels for Mg2+is in the physiological range, with Mg2+binding with an IC50of 0.53 mM in HCN2 channels and 0.82 mM in HCN1 channels at +50 mV. The effective electrical distance for the Mg2+binding site was found to be 0.19 for HCN1 channels, suggesting that the binding site is in the pore. Removing a cysteine in the selectivity filter of HCN1 channels reduced the affinity for Mg2+, suggesting that this residue forms part of the binding site deep within the pore. Our results suggest that Mg2+acts as a voltage-dependent pore blocker and, therefore, reduces outward currents through HCN channels. The pore-blocking action of Mg2+may play an important physiological role, especially for the slowly gating HCN2 and HCN4 channels. Mg2+could potentially block outward hyperpolarizing HCN currents at the plateau of action potentials, thus preventing a premature termination of the action potential.