Permeant anions control gating of calcium-dependent chloride channels
Permeant anions control gating of calcium-dependent chloride channels
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DOI：
10.1007/s00232-004-0659-x
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发表时间：
2004-04-01
影响因子：
2.4
通讯作者：
Arreola, J
中科院分区：
文献类型：
--
作者：
Perez-Cornejo, P;De Santiago, JA;Arreola, J
采用全细胞膜片钳技术研究了外源性阴离子（SCN-、NO3-、I-、Br-、F-、谷氨酸和天冬氨酸）对大鼠腮腺腺泡细胞Ca ~（2+）依赖性Cl ~-通道门控的影响。用外源阴离子取代Cl-引起的电流反转电位的变化，根据渗透率比（P-x/P-Cl），给出如下选择性顺序：SCN- > I- > NO_3- > Br- > Cl- > F- >天冬氨酸>谷氨酸。利用连续介质静电模型，我们计算出这种溶致序列是由阴离子和一个有效介电常数近似为23的可极化隧道之间的相互作用引起的。我们的数据显示，P-x/P-Cl > 1的阴离子以不依赖于电压的方式加速活化动力学，并减缓失活动力学。此外，渗透性阴离子增强全细胞电导（g，表观开放概率的指数）在电压依赖性的方式，并移动了膜电位-g曲线。所有这些效应都是由阴离子产生的，其有效性遵循选择性顺序。为了解释渗透性阴离子对活化动力学和g（Cl）的影响，我们提出在通道中有2个不同的阴离子结合位点。一个位点位于电场外并控制通道活化动力学，而第二个位点位于孔内并控制全细胞电导。因此，渗透性阴离子与这两个位点的相互作用阻碍了关闭机制并使通道稳定在开放状态。
The effects of external anions (SCN-, NO3-, I-, Br-, F-, glutamate, and aspartate) on gating of Ca2+-dependent Cl- channels from rat parotid acinar cells were studied using the whole-cell configuration of the patch-clamp technique. Shifts in the reversal potential of the current induced by replacement of external Cl- with foreign anions, gave the following selectivity sequence based on permeability ratios (P-x/P-Cl): SCN- > I- > NO3- > Br- > Cl- > F- > aspartate > glutamate. Using a continuum electrostatic model we calculated that this lyotropic sequence resulted from the interaction between anions and a polarizable tunnel with an effective dielectric constant of similar to23. Our data revealed that anions with P-x/P-Cl > 1 accelerated activation kinetics in a voltage-independent manner and slowed deactivation kinetics. Moreover, permeant anions enhanced whole-cell conductance (g, an index of the apparent open probability) in a voltage-dependent manner, and shifted leftward the membrane potential-g curves. All of these effects were produced by the anions with an effectiveness that followed the selectivity sequence. To explain the effects of permeant anions on activation kinetics and g(Cl) we propose that there are 2 different anion-binding sites in the channel. One site is located outside the electrical field and controls channel activation kinetics, while a second site is located within the pore and controls whole-cell conductance. Thus, interactions of permeant anions with these two sites hinder the closing mechanism and stabilize the channel in the open state.