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首页> 外文期刊>Journal of Neurophysiology >G-protein-modulated Ca(2+) current with slowed activation does not alter the kinetics of action potential-evoked Ca(2+) current.
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G-protein-modulated Ca(2+) current with slowed activation does not alter the kinetics of action potential-evoked Ca(2+) current.

机译：G蛋白调制的Ca（2+）电流与缓慢的激活不会改变动作电位诱发的Ca（2+）电流的动力学。

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摘要

We have studied voltage-dependent inhibition of N-type calcium currents to investigate the effects of G-protein modulation-induced alterations in channel gating on action potential-evoked calcium current. In isolated chick ciliary ganglion neurons, GTPgammaS produced voltage-dependent inhibition that exhibited slowed activation kinetics and was partially relieved by a conditioning prepulse. Using step depolarizations to evoke calcium current, we measured tail current amplitudes on abrupt repolarization to estimate the time course of calcium channel activation from 1 to 30 ms. GTPgammaS prolonged significantly channel activation, consistent with the presence of kinetic slowing in the modulated whole cell current evoked by 100-ms steps. Since kinetic slowing is caused by an altered voltage dependence of channel activation (such that channels require stronger or longer duration depolarization to open), we asked if GTPgammaS-induced modulation would alter the time course of calcium channel activation during an action potential. Using an action potential waveform as a voltage command to evoke calcium current, we abruptly repolarized to -80 mV at various time points during the repolarization phase of the action potential. The resulting tail current was used to estimate the relative number of calcium channels that were open. Using action potential waveforms of either 2.2- or 6-ms duration at half-amplitude, there were no differences in the time course of calcium channel activation, or in the percent activation at any time point tested during the repolarization, when control and modulated currents were compared. It is also possible that modulated channels might open briefly and that these reluctant openings would effect the time course of action potential-evoked calcium current. However, when control and modulated currents were scaled to the same peak amplitude and superimposed, there was no difference in the kinetics of the two currents. Thus voltage-dependent inhibition did not alter the kinetics of action potential-evoked current. These results suggest that G-protein-modulated channels do not contribute significantly to calcium current evoked by a single action potential.
机译：我们研究了N型钙电流的电压依赖性抑制作用，以研究G蛋白调节诱导的通道门控变化对动作电位诱发的钙电流的影响。在孤立的雏鸡睫状神经节神经元中，GTPgammaS产生电压依赖性抑制，其显示出较慢的激活动力学，并通过调节预脉冲而部分缓解。使用逐步去极化来诱发钙电流，我们测量了突然再极化时的尾电流幅值，以估计钙通道激活的时间过程为1到30 ms。 GTPgammaS显着延长了通道激活，这与以100毫秒为步长诱发的调制全细胞电流中动力学减慢的存在一致。由于动力学减慢是由通道激活的电压依赖性改变引起的（因此通道需要更强或更长时间的去极化才能打开），我们询问了GTPgammaS诱导的调节是否会在动作电位期间改变钙通道激活的时间过程。使用动作电位波形作为引发钙电流的电压命令，我们在动作电位的重新极化阶段的各个时间点突然重新极化到-80 mV。产生的尾电流用于估计打开的钙通道的相对数量。使用半振幅持续时间为2.2毫秒或6毫秒的动作电位波形，在控制和调制电流下，钙离子通道激活的时间过程或复极化过程中测试的任何时间点的激活百分比均无差异。比较。调制通道可能会短暂打开，而这些勉强打开也会影响动作电位诱发的钙电流的时间变化。但是，当控制电流和调制电流按比例缩放到相同的峰值幅度并叠加时，两种电流的动力学没有差异。因此，电压依赖性抑制作用不会改变动作电位诱发电流的动力学。这些结果表明，G蛋白调节通道对单个动作电位诱发的钙电流没有明显贡献。

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