Kwan Daniel C H, Eduljee Cyrus, Lee Logan, Zhang Shetuan, Fedida David, Kehl Steven J
Department of Physiology, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z3.
Biophys J. 2004 Apr;86(4):2238-50. doi: 10.1016/S0006-3495(04)74282-4.
By examining the consequences both of changes of [K+]o and of point mutations in the outer pore mouth, our goal was to determine if the mechanism of the block of Kv1.5 ionic currents by external Ni2+ is similar to that for proton block. Ni2+ block is inhibited by increasing [K+]o, by mutating a histidine residue in the pore turret (H463Q) or by mutating a residue near the pore mouth (R487V) that is the homolog of Shaker T449. Aside from a slight rightward shift of the Q-V curve, Ni2+ had no effect on gating currents. We propose that, as with Ho+, Ni2+ binding to H463 facilitates an outer pore inactivation process that is antagonized by Ko+ and that requires R487. However, whereas Ho+ substantially accelerates inactivation of residual currents, Ni2+ is much less potent, indicating incomplete overlap of the profiles of these two metal ions. Analyses with Co2+ and Mn2+, together with previous results, indicate that for the first-row transition metals the rank order for the inhibition of Kv1.5 in 0 mM Ko+ is Zn2+ (KD approximately 0.07 mM) > or = Ni2+) (KD approximately 0.15 mM) > Co2+ (KD approximately 1.4 mM) > Mn2+ (KD > 10 mM).
通过研究细胞外钾离子浓度（[K⁺]o）变化以及外孔口点突变的后果，我们的目标是确定细胞外镍离子（Ni²⁺）阻断Kv1.5离子电流的机制是否与质子阻断机制相似。增加[K⁺]o、将孔壁上的组氨酸残基突变（H463Q）或使孔口附近与Shaker T449同源的残基突变（R487V），均可抑制Ni²⁺阻断。除了Q-V曲线略有右移外，Ni²⁺对门控电流没有影响。我们提出，与H⁺一样，Ni²⁺与H463结合促进了一种外孔失活过程，该过程受到K⁺的拮抗且需要R487参与。然而，虽然H⁺能显著加速残余电流的失活，但Ni²⁺的作用要弱得多，这表明这两种金属离子的作用模式并不完全重叠。用Co²⁺和Mn²⁺进行的分析以及先前的结果表明，对于第一排过渡金属，在0 mM K⁺条件下抑制Kv1.5的能力排序为：Zn²⁺（KD约为0.07 mM）≥Ni²⁺（KD约为0.15 mM）＞Co²⁺（KD约为1.4 mM）＞Mn²⁺（KD＞10 mM）。
