Hadley R W, Lederer W J
Department of Physiology, School of Medicine, University of Maryland, Baltimore 21201.
J Gen Physiol. 1991 Aug;98(2):265-85. doi: 10.1085/jgp.98.2.265.
Nonlinear capacitative current (charge movement) was compared to the Ca current (ICa) in single guinea pig ventricular myocytes. It was concluded that the charge movement seen with depolarizing test steps from -50 mV is dominated by L-type Ca channel gating current, because of the following observations. (a) Ca channel inactivation and the immobilization of the gating current had similar voltage and time dependencies. The degree of channel inactivation was directly proportional to the amount of charge immobilization, unlike what has been reported for Na channels. (b) The degree of Ca channel activation was closely correlated with the amount of charge moved at all test potentials between -40 and +60 mV. (c) D600 was found to reduce the gating current in a voltage- and use-dependent manner. D600 was also found to induce "extra" charge movement at negative potentials. (d) Nitrendipine reduced the gating current in a voltage-dependent manner (KD = 200 nM at -40 mV). However, nitrendipine did not increase charge movement at negative test potentials. Although contamination of the Ca channel gating current from other sources cannot be fully excluded, it was not evident in the data and would appear to be small. However, it was noted that the amount of Ca channel gating charge was quite large compared with the magnitude of the Ca current. Indeed, the gating current was found to be a significant contaminant (19 +/- 7%) of the Ca tail currents in these cells. In addition, it was found that Ca channel rundown did not diminish the gating current. These results suggest that Ca channels can be "inactivated" by means that do not affect the voltage sensor.
在单个豚鼠心室肌细胞中，将非线性电容电流（电荷移动）与钙电流（ICa）进行了比较。基于以下观察结果得出结论：从 -50 mV 进行去极化测试步骤时观察到的电荷移动主要由 L 型钙通道门控电流主导。(a) 钙通道失活和门控电流的固定具有相似的电压和时间依赖性。与钠通道的情况不同，通道失活程度与电荷固定量成正比。(b) 在 -40 至 +60 mV 之间的所有测试电位下，钙通道激活程度与移动的电荷量密切相关。(c) 发现 D600 以电压和使用依赖性方式降低门控电流。还发现 D600 在负电位下诱导“额外”的电荷移动。(d) 尼群地平以电压依赖性方式降低门控电流（在 -40 mV 时 KD = 200 nM）。然而，尼群地平在负测试电位下不会增加电荷移动。尽管不能完全排除来自其他来源的钙通道门控电流的污染，但在数据中并不明显，似乎很小。然而，值得注意的是，与钙电流的大小相比，钙通道门控电荷量相当大。实际上，在这些细胞中发现门控电流是钙尾电流的一个重要污染物（19 +/- 7%）。此外，发现钙通道功能衰减不会降低门控电流。这些结果表明，钙通道可以通过不影响电压传感器的方式“失活”。
