Ion binding in the open HCN pacemaker channel pore: fast mechanisms to shape "slow" channels.
Ion binding in the open HCN pacemaker channel pore: fast mechanisms to shape "slow" channels.
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DOI：
10.1085/jgp.200709868
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发表时间：
2008-03
期刊：
影响因子：
--
通讯作者：
Tibbs GR
中科院分区：
文献类型：
--
作者：
Lyashchenko AK;Tibbs GR
IH起搏器通道携带一种混合的单价阳离子电流，在生理离子梯度下，该电流在10 - 34 mV时反转，反映出对K的选择性为4：1。然而，IH通道相对于渗透性离子显示出异常行为，使得（a）开放通道不表现出假定独立性所预期的向外整流;（B）门控和选择性对外部呈现的渗透性离子的身份和浓度敏感;（c）通道携带内向Na电流的能力需要外部K的存在，即使K在负电压下是次要的电荷载流子。在这里，我们表明，开放的HCN通道（超极化激活，环核苷酸敏感孔形成亚基的IH）进行快速，电压依赖性块细胞内镁的方式，表明离子结合接近，或内，选择性过滤器。消除内部二价离子阻断揭示了（a）传导的K依赖性是通过孔内位点的K占据介导的，并且这些位点的不对称占据和/或与通量的偶联进一步形成离子流，和（B）孔的K-空位和K-占据状态之间平衡的动力学（10-20 μs或更快）接近于孔被K单独占据时的离子渡越时间（约0.5-3 μs），这一发现表明，任一离子：涉及Na的离子排斥足以支持通量（尽管速率低于我们的检测阈值）和/或孔在非导电和导电构型之间经历快速的渗透离子敏感平衡。生物药理学上，进一步探索Mg位点和孔内Na和K的相互作用将告诉我们很多关于这个不寻常的孔的结构和操作。从生理学上讲，这些结果表明，“慢”起搏通道可能有助于动态塑造快速过程，如钠-钾或钙动作电位。
IH pacemaker channels carry a mixed monovalent cation current that, under physiological ion gradients, reverses at ∼−34 mV, reflecting a 4:1 selectivity for K over Na. However, IH channels display anomalous behavior with respect to permeant ions such that (a) open channels do not exhibit the outward rectification anticipated assuming independence; (b) gating and selectivity are sensitive to the identity and concentrations of externally presented permeant ions; (c) the channels' ability to carry an inward Na current requires the presence of external K even though K is a minor charge carrier at negative voltages. Here we show that open HCN channels (the hyperpolarization-activated, cyclic nucleotide sensitive pore forming subunits of IH) undergo a fast, voltage-dependent block by intracellular Mg in a manner that suggests the ion binds close to, or within, the selectivity filter. Eliminating internal divalent ion block reveals that (a) the K dependence of conduction is mediated via K occupancy of site(s) within the pore and that asymmetrical occupancy and/or coupling of these sites to flux further shapes ion flow, and (b) the kinetics of equilibration between K-vacant and K-occupied states of the pore (10–20 μs or faster) is close to the ion transit time when the pore is occupied by K alone (∼0.5–3 μs), a finding that indicates that either ion:ion repulsion involving Na is adequate to support flux (albeit at a rate below our detection threshold) and/or the pore undergoes rapid, permeant ion-sensitive equilibration between nonconducting and conducting configurations. Biophysically, further exploration of the Mg site and of interactions of Na and K within the pore will tell us much about the architecture and operation of this unusual pore. Physiologically, these results suggest ways in which “slow” pacemaker channels may contribute dynamically to the shaping of fast processes such as Na-K or Ca action potentials.
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DOI：
10.1085/jgp.200609638
发表时间：
2006-11
期刊：
The Journal of general physiology
影响因子：
--
作者：
Blunck R;Cordero-Morales JF;Cuello LG;Perozo E;Bezanilla F
通讯作者：
Bezanilla F
影响因子：
5.3
作者：
Bruening-Wright, Andrew;Larsson, H. Peter
通讯作者：
Larsson, H. Peter
DOI：
10.1152/physiologyonline.2002.17.1.32
发表时间：
2002-02-01
期刊：
NEWS IN PHYSIOLOGICAL SCIENCES
影响因子：
--
作者：
Accili, EA;Proenza, C;DiFrancesco, D
通讯作者：
DiFrancesco, D
影响因子：
5.5
作者：
Elinder, Fredrik;Mannikko, Roope;Larsson, H. Peter
通讯作者：
Larsson, H. Peter
影响因子：
5.3
作者：
Fogle, Keri J.;Lyashchenko, Alex K.;Tibbs, Gareth R.
通讯作者：
Tibbs, Gareth R.