Department of Neurobiology, Harvard Medical School, Boston, MA 02115, USA.
Neuron. 2012 Sep 20;75(6):1081-93. doi: 10.1016/j.neuron.2012.08.033.
Tetrodotoxin (TTX)-sensitive sodium channels carry large transient currents during action potentials and also "persistent" sodium current, a noninactivating TTX-sensitive current present at subthreshold voltages. We examined gating of subthreshold sodium current in dissociated cerebellar Purkinje neurons and hippocampal CA1 neurons, studied at 37°C with near-physiological ionic conditions. Unexpectedly, in both cell types small voltage steps at subthreshold voltages activated a substantial component of transient sodium current as well as persistent current. Subthreshold EPSP-like waveforms also activated a large component of transient sodium current, but IPSP-like waveforms engaged primarily persistent sodium current with only a small additional transient component. Activation of transient as well as persistent sodium current at subthreshold voltages produces amplification of EPSPs that is sensitive to the rate of depolarization and can help account for the dependence of spike threshold on depolarization rate, as previously observed in vivo.
河豚毒素 (TTX) 敏感型钠离子通道在动作电位期间携带大的瞬态电流，并且还存在“持续”的 TTX 敏感型钠离子电流，即在亚阈电压下存在的非失活的 TTX 敏感型电流。我们在 37°C 下使用接近生理离子条件，在分离的小脑浦肯野神经元和海马 CA1 神经元中检查了阈下钠电流的门控。出乎意料的是，在这两种细胞类型中，亚阈电压的小电压阶跃会激活瞬态钠电流和持续电流的相当大的组成部分。阈下 EPSP 样波形也会激活大量的瞬态钠电流，但 IPSP 样波形主要参与持续的钠电流，只有少量额外的瞬态成分。在阈下电压下激活瞬态和持续的钠电流会放大 EPSP，这种放大对去极化的速率敏感，并可以帮助解释先前在体内观察到的尖峰阈值对去极化速率的依赖性。
