Monovalent permeability, rectification, and ionic block of store-operated calcium channels in Jurkat T lymphocytes.
Monovalent permeability, rectification, and ionic block of store-operated calcium channels in Jurkat T lymphocytes.
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DOI：
10.1085/jgp.111.4.521
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发表时间：
1998-04
期刊：
影响因子：
--
通讯作者：
Cahalan MD
中科院分区：
文献类型：
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作者：
Kerschbaum HH;Cahalan MD
我们使用全细胞记录来表征离子渗透、整流和阻断Jurkat T淋巴细胞中通过钙释放激活的钙（CRAC）通道的单价电流。在生理条件下，CRAC通道对Ca 2+表现出高度的选择性，但当外部二价离子降低至微摩尔水平时，可以诱导其携带缓慢下降的Na+电流。使用一系列的有机阳离子作为探针的不同大小，我们测量的反转电位和计算的渗透率比相对于Na+，PX/P Na，为了估计的导电孔的直径。铵离子（NH 4+）的相对渗透性最高（PNH 4/PNa = 1.37）。最大的渗透离子，四甲基铵的直径为0.55 nm，具有P TMA/P Na为0.09。N-甲基-D-葡糖胺（0.50 × 0.64 × 1.20 nm）无可测渗透性。 除了携带单价电流之外，NH 4+在降低[Ca 2 +]o时减少单价电流的缓慢下降（“失活”）。细胞外NH 4+的这种动力学效应可以通过细胞内pH（pHi）的增加来解释，因为将细胞内pH升高到8以上降低了失活的程度。此外，降低pHi降低了通过pKa为6.8的CRAC通道的单价和二价电流幅度。在几种通道类型中，Mg 2+已被证明通过电压依赖性阻断机制产生整流。从移液器溶液中去除Mg 2+允许大的外向单价电流流过CRAC通道，同时还增加通道的相对Cs+电导并消除单价电流的失活。玻尔兹曼拟合表明，细胞内Mg 2+通过以电压依赖性方式阻断而有助于向内整流，zδ乘积为1.88。还发现来自外部的Ca 2+阻断是电压依赖性的，zδ为1.62。这些实验表明，CRAC通道，像电压门控的Ca 2+通道，通过选择性结合在一个大的孔与电流-电压特性由内部Mg 2+形成的Ca 2+的选择性。
We used whole-cell recording to characterize ion permeation, rectification, and block of monovalent current through calcium release-activated calcium (CRAC) channels in Jurkat T lymphocytes. Under physiological conditions, CRAC channels exhibit a high degree of selectivity for Ca2+, but can be induced to carry a slowly declining Na+ current when external divalent ions are reduced to micromolar levels. Using a series of organic cations as probes of varying size, we measured reversal potentials and calculated permeability ratios relative to Na+, P X/P Na, in order to estimate the diameter of the conducting pore. Ammonium (NH4 +) exhibited the highest relative permeability (P NH4/P Na = 1.37). The largest permeant ion, tetramethylammonium with a diameter of 0.55 nm, had P TMA/P Na of 0.09. N-methyl-d-glucamine (0.50 × 0.64 × 1.20 nm) was not measurably permeant. In addition to carrying monovalent current, NH4 + reduced the slow decline of monovalent current (“inactivation”) upon lowering [Ca2+]o. This kinetic effect of extracellular NH4 + can be accounted for by an increase in intracellular pH (pHi), since raising intracellular pH above 8 reduced the extent of inactivation. In addition, decreasing pHi reduced monovalent and divalent current amplitudes through CRAC channels with a pKa of 6.8. In several channel types, Mg2+ has been shown to produce rectification by a voltage-dependent block mechanism. Mg2+ removal from the pipette solution permitted large outward monovalent currents to flow through CRAC channels while also increasing the channel's relative Cs+ conductance and eliminating the inactivation of monovalent current. Boltzmann fits indicate that intracellular Mg2+ contributes to inward rectification by blocking in a voltage-dependent manner, with a zδ product of 1.88. Ca2+ block from the outside was also found to be voltage dependent with zδ of 1.62. These experiments indicate that the CRAC channel, like voltage-gated Ca2+ channels, achieves selectivity for Ca2+ by selective binding in a large pore with current–voltage characteristics shaped by internal Mg2+.