Voltage-dependence of virus-encoded miniature K+ channel Kcv
Voltage-dependence of virus-encoded miniature K+ channel Kcv
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DOI：
10.1007/s00232-001-0147-5
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发表时间：
2002-05-01
影响因子：
2.4
通讯作者：
Moroni, A
中科院分区：
文献类型：
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作者：
Gazzarrini, S;Van Etten, JL;Moroni, A
Kcv 是由草履虫小球藻病毒 1 (PBVC-1) 编码的 K+ 选择性通道。这种蛋白质是迄今为止已知的最小的功能性 K+ 通道，在非洲爪蟾卵母细胞中的表达揭示了电压钳步骤期间的瞬时和时间依赖性成分。这两种成分对抑制剂金刚烷胺具有相同的敏感性，这意味着它们反映了同一通道的不同动力学特征。大约70%的通道始终畅通；在超极化电压下，时间依赖性通道 (30%) 以电压依赖性方式打开，在约 -70 mV 时达到半最大激活。在极端的正电压和负电压下，开路电导以电压依赖性方式降低。为了检查 Kcv 电压依赖性的机制，我们中和了亲脂性 N 末端的两个带电氨基酸。然而，这种双重突变对通道的电压依赖性没有影响，从而否定了这些带电氨基酸代表膜嵌入电压传感器的可能性。我们考虑了外部二价阳离子的阻断是否与通道的电压依赖性有关。外部 Ca2+ 浓度降低十倍时，Kcv 电流增加约 4 倍。这种电流的显着增加是在降低 Ca2+ 时观察到的，但不是在降低 Mg2+ 时观察到的，并且与电压无关。这些数据表明了一种 Ca2+ 选择性但与电压无关的通道电导调节机制。
Kcv is a K+-selective channel encoded by the Paramecium bursaria Chlorella virus 1 (PBVC-1). Expression of this protein, so far the smallest known functional K+ channel, in Xenopus oocytes reveals an instantaneous and a time-dependent component during voltage-clamp steps. These two components have an identical sensitivity to the inhibitor amantadine, implying that they reflect distinct kinetic features of the same channel. About 70% of the channels are always open; at hyperpolarizing voltages the time-dependent channels (30%) open in a voltage-dependent manner reaching half-maximal activation at about -70 mV. At both extreme positive and negative voltages the open-channel conductance decreases in a voltage-dependent manner. To examine the mechanism underlying the voltage-dependence of Kcv we neutralized the two charged amino acids in the lipophilic N-terminus. However, this double mutation had no effect on the voltage-dependence of the channel, ruling against the possibility that these charged amino acids represent a membrane-embedded voltage sensor. We have considered whether a block by external divalent cations is involved in the voltage-dependence of the channel, The Kcv current was increased about 4-fold on reduction of external Ca2+ concentration by a factor of ten. This pronounced increase in current was observed on lowering Ca2+ but not Mg2+ and was voltage-independent. These data indicate a Ca2+-selective, but voltage-independent mechanism for regulation of channel conductance.