Sodium channel gating in clonal pituitary cells. The inactivation step is not voltage dependent.
Sodium channel gating in clonal pituitary cells. The inactivation step is not voltage dependent.
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克隆垂体细胞中的钠通道门控。灭活步骤不取决于电压。
DOI：
10.1085/jgp.94.2.213
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发表时间：
1989-08
影响因子：
3.8
通讯作者：
Armstrong, C M
中科院分区：
文献类型：
--
作者：
Cota, G;Armstrong, C M
我们通过比较酶解失活前后的记录，确定了克隆垂体（GH3）细胞Na通道失活的时间过程。将细胞置于全细胞膜片钳中，内培养基中加入木瓜蛋白酶。在10分钟的过程中慢慢去除失活，使在酶起作用之前获得对照记录成为可能。木瓜蛋白酶导致小的去极化（接近-40 mV）电流幅度的增加（4-100倍），而大的去极化（+40 mV约1.5倍）电流幅度的增加要小得多。由于技术原因，有时在没有Na+的情况下向外研究比较方便。该条件下瞬时I-V （iv）曲线在木瓜蛋白酶作用前呈非线性，蛋白酶作用后呈近似线性。用INa-V曲线除以ivv曲线得到的木瓜蛋白酶作用后的gNa-V曲线左移至少20 mV，曲线变陡。在没有木瓜蛋白酶的情况下，自发左移5-10毫伏。根据以下证据，发现失活步骤的速率仅在-100 mV到+60 mV之间略有变化。(a)木瓜蛋白酶作用前，失活率随电压饱和，在+20 ~ +60 mV范围内恒定。(b)我们用一个简短的脉冲激活通道，并研究了电流在将电压改变到一秒时的时间过程，通常是更负的水平（内部和外部都有Na+）。通过对比控制迹线与去失活后的迹线，得到各电压下失活的时间过程。当考虑5-10 mV自发位移时，从-100 mV到+60 mV的失活率变化小于10%。这些数据是根据Na通道的现有模型考虑的。
We have determined the time course of Na channel inactivation in clonal pituitary (GH3) cells by comparing records before and after the enzymatic removal of inactivation. The cells were subjected to whole- cell patch clamp, with papain included in the internal medium. Inactivation was slowly removed over the course of 10 min, making it possible to obtain control records before the enzyme acted. Papain caused a large (4-100x) increase in current magnitude for small depolarizations (near -40 mV), and a much smaller increase for large ones (approximately 1.5x at +40 mV). For technical reasons it was sometimes convenient to study outward INa recorded with no Na+ outside. The instantaneous I-V (IIV) curve in this condition was nonlinear before papain, and more nearly linear afterwards. The gNa-V curve after papain, obtained by dividing the INa-V curve by the IIV curve, was left- shifted by at least 20 mV and steepened. A spontaneous 5-10 mV left shift occurred in the absence of papain. The rate of the inactivation step was found to vary only slightly from -100 mV to +60 mV, based on the following evidence. (a) Before papain, inactivation rate saturated with voltage and was constant from +20 to +60 mV. (b) We activated the channels with a brief pulse, and studied the time course of the current on changing the voltage to a second, usually more negative level (Na+ present internally and externally). The time course of inactivation at each voltage was obtained by comparing control traces with those after inactivation was removed. When the 5-10-mV spontaneous shift was taken into account, inactivation rate changed by less than 10% from -100 to +60 mV. The data are considered in terms of existing models of the Na channel.