Gera S, Byerly L
Department of Biological Sciences, University of Southern California, Los Angeles, California 90089-2520, USA.
Biophys J. 1999 Jun;76(6):3076-88. doi: 10.1016/S0006-3495(99)77460-6.
We have developed two methods to measure Ca2+ channel inactivation in Lymnaea neurons-one method, based upon the conventional double-pulse protocol, uses currents during a moderately large depolarizing pulse, and the other uses tail currents after a very strong activating pulse. Both methods avoid contamination by proton currents and are unaffected by rundown of Ca2+ current. The magnitude of inactivation measured differs for the two methods; this difference arises because the measurement of inactivation is inherently dependent upon the test pulse voltage used to monitor the Ca2+ channel conductance. We discuss two models that can generate such test pulse dependence of inactivation measurements-a two-channel model and a two-open-state model. The first model accounts for this by assuming the existence of two types of Ca2+ channels, different proportions of which are activated by the different test pulses. The second model assumes only one Ca2+ channel type, with two closed and open states; in this model, the test pulse dependence is due to the differential activation of channels in the two closed states by the test pulses. Test pulse dependence of inactivation measurements of Ca2+ channels may be a general phenomenon that has been overlooked in previous studies.
我们开发了两种方法来测量椎实螺神经元中Ca2+通道的失活——一种方法基于传统的双脉冲方案，利用适度大的去极化脉冲期间的电流，另一种方法利用非常强的激活脉冲后的尾电流。两种方法都避免了质子电流的污染，并且不受Ca2+电流衰减的影响。两种方法测量的失活幅度不同；这种差异的产生是因为失活的测量本质上取决于用于监测Ca2+通道电导的测试脉冲电压。我们讨论了两种可以产生这种失活测量对测试脉冲的依赖性的模型——双通道模型和双开放态模型。第一个模型通过假设存在两种类型的Ca2+通道来解释这一点，不同比例的这两种通道由不同的测试脉冲激活。第二个模型仅假设一种Ca2+通道类型，具有两个关闭和开放状态；在这个模型中，测试脉冲依赖性是由于测试脉冲对两个关闭状态下通道的差异激活。Ca2+通道失活测量对测试脉冲的依赖性可能是一种在以前的研究中被忽视的普遍现象。
