Single L-type calcium channel conductance with physiological levels of calcium in chick ciliary ganglion neurons
Single L-type calcium channel conductance with physiological levels of calcium in chick ciliary ganglion neurons
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DOI：
10.1113/jphysiol.1996.sp021665
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发表时间：
1996-10-01
影响因子：
5.5
通讯作者：
Stanley, EF
中科院分区：
文献类型：
--
作者：
Church, PJ;Stanley, EF
1.采用石英玻璃微移液器细胞贴壁膜片钳高电流分辨技术研究鸡睫状神经节神经元L型钙通道.当Ba 2+为电荷载流子时，观察到单个开通道电流幅度，在110 mM钡下电导为26 pS。然而，与110 mM钙两个电流波动幅度进行了观察。这些被称为低和高波动幅度，Ca-L和Ca-H，电导分别为8.8和12 pS。这两个水平可能反映了两种不同的通道物种。基于对失活的抗性、电导和二氢吡啶敏感性，将Ca-L鉴定为L型钙通道.单通道电流波动可以检测到低至1.0 mM的钙浓度。虽然单位电导（伽马）是更大的钡比钙在每一个浓度测试，电导的浓度依赖性是类似的伽马（Ba），伽马（CaH）和伽马（CaL）。将这些电导的浓度依赖性与朗缪尔等温线拟合得到钡、Ca-L和Ca-H的K-D估计值分别为4.7、5.6和5.0 mM。L-型通道的单通道电导（γ（L））可以通过以下关系描述：电导（以pS计）= 9.2/（1 + 5.6/[Ca]），其中[Ca]是1.0-110 mM范围内的外部钙浓度。因此，在2 mM的生理外部钙浓度下，电导为2.4pS.5。通过L型钙通道的Ca 2+转运对生理范围内的外部钙浓度变化特别敏感，但在约10 mM时接近饱和。这一特性可以优化细胞对周围钙浓度微小变化的反应，同时限制异常高钙水平存在下的过量进入。
1. Single L-type calcium channels in chick ciliary ganglion neurons were studied at high current resolution in cell-attached patch recordings using quartz-glass micropipettes.2. A single open-channel current amplitude was observed when Ba2+ was the charge carrier with a conductance of 26 pS at 110 mM barium. However, with 110 mM calcium two current fluctuation amplitudes were observed. These were termed low and high fluctuation amplitudes, Ca-L and Ca-H, and had conductances of 8.8 and 12 pS, respectively. These two levels probably reflect two different channel species. Ca-L was identified as an L-type calcium channel on the basis of resistance to inactivation, conductance, and dihydropyridine sensitivity.3. Single-channel current fluctuations could be detected with calcium concentrations as low as 1.0 mM. Although the unitary conductance (gamma) was much greater with barium than calcium at every concentration tested, the concentration dependence of conductance was similar for gamma(Ba), gamma(CaH) and gamma(CaL). Fitting the concentration dependencies of these conductances with a Langmuir isotherm gave K-D estimates of 4.7, 5.6 and 5.0 mM for barium, Ca-L and Ca-H, respectively.4. The single-channel conductance of the L-type channel (gamma(L)) can be described by the relation: conductance (in pS) = 9.2/(1 + 5.6/[Ca]) where [Ca] is the external calcium concentration in the 1.0-110 mM range. Thus, at a physiological external calcium concentration of 2 mM the conductance is 2.4 pS.5. Ca2+ transport through the L-type calcium channel is particularly sensitive to changes in external calcium concentration in the physiological range but approaches saturation at about 10 mM. This characteristic may optimize the responsiveness of the cell to small changes in ambient calcium concentrations while limiting excess entry in the presence of abnormally high calcium levels.