Discrete Ba2+ block as a probe of ion occupancy and pore structure in the high-conductance Ca2+ -activated K+ channel.
Discrete Ba2+ block as a probe of ion occupancy and pore structure in the high-conductance Ca2+ -activated K+ channel.
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离散的BA2+块作为高导通Ca2+活化的K+通道中离子占用和孔结构的探针。
DOI：
10.1085/jgp.92.5.569
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发表时间：
1988-11
影响因子：
3.8
通讯作者：
Miller, C
中科院分区：
文献类型：
--
作者：
Neyton, J;Miller, C
本研究将大鼠骨骼肌高电导钙激活的K+通道掺入平面磷脂双层膜，研究Ba2+对单个通道的离散阻断作用。当150 mM K+在内液中保持不变时，在100-1000 mM范围内增加外部K+会增加Ba2+的解离速率。这种“增强效应”在K+浓度下工作，比前面所述的“锁定”效应高3-4个数量级，取决于外加电压，随K+浓度饱和，与Na+浓度无关。Ba2+关断率的电压依赖关系随着外部K+的不同而不同，这表明K+从外部进入通道，迫使Ba2+解离到内部溶液。当K+在外部溶液中保持不变时，当内部K+在0-50 mm范围内升高时，Ba2+的脱附率降低。这种“锁定”效应与外部类似(Neyton和Miller，1988)，不同之处在于，内部锁定位点亲和力较低，对K+的偏好仅为Na+的五倍。所有这些结果有力地证明了这一通道的传导途径包含四个对K+具有很高亲和力的位置，在正常的传导条件下，所有这些位置都可以同时被占据。根据这一观点，这种高离子占有率导致的相互不稳定导致了这种K+特异性通道的异常高的电导。
In this study, high-conductance Ca2+-activated K+ channels from rat skeletal muscle were incorporated into planar phospholipid bilayers, and discrete blockade of single channels by Ba2+ was studied. With 150 mM K+ held constant in the internal solution, increasing external K+ over the range 100-1,000 mM raises the rate of Ba2+ dissociation. This "enhancement effect," which operates at K+ concentrations 3-4 orders of magnitude higher than those required for the "lockin" effect described previously, depends on applied voltage, saturates with K+ concentration, and is not observed with Na+. The voltage dependence of the Ba2+ off-rate varies with external K+ in a way suggesting that K+, entering the channel from the external side, forces Ba2+ dissociation to the internal solution. With K+ held fixed in the external solution, the Ba2+ off-rate decreases as internal K+ is raised over the range 0- 50 mM. This "lock-in" effect is similar to that seen on the external side (Neyton and Miller, 1988), except that the internal lock-in site is of lower affinity and shows only a fivefold preference for K+ over Na+. All the results taken together argue strongly that this channel's conduction pathway contains four sites of very high affinity for K+, all of which may be simultaneously occupied under normal conducting conditions. According to this view, the mutual destabilization resulting from this high ionic occupancy leads to the unusually high conductance of this K+-specific channel.