Rathouz M, Trussell L
Department of Physiology, University of Wisconsin, Madison, Wisconsin 53706, USA.
J Neurophysiol. 1998 Dec;80(6):2824-35. doi: 10.1152/jn.1998.80.6.2824.
Characterization of outward currents in neurons of the avian nucleus magnocellularis. J. Neurophysiol. 80: 2824-2835, 1998. Neurons of the nucleus magnocellularis (NM) preserve the timing of auditory signals through the convergence of a variety of voltage- and ligand-gated ion channels. To understand better how these channels interact, we have characterized the kinetics, voltage sensitivity, and pharmacology of outward currents of NM neurons in brain slices. The reversal potential (Erev) of outward currents varied with potassium concentration as expected for currents carried by potassium. However, Erev was consistently more positive than the Nernst potential for potassium (EK). Deviation of Erev from the calculated EK most likely arose from potassium accumulation in extracellular spaces by potassium conductances active at rest and during depolarizing steps. Three outward potassium currents were studied that varied in voltage and pharmacological sensitivity. A tetraethylammonium (TEA)-sensitive, high-threshold current was activated within 1-5 ms of the onset of depolarization, with a half-maximal activation voltage (V1/2) of -19 mV. It was blocked partially by 4-aminopyridine (4-AP) and was the dominant ionic conductance of NM neurons. A dendrotoxin-I (DTX) and 4-AP-sensitive, low-threshold current had a V1/2 of -58 mV, rapid activation kinetics, and only partial inactivation, with decay time constants between 20 and 100 ms. A rapidly inactivating current was observed that was resistant to TEA and DTX and was blocked by intracellular Cs+. The transient current was inactivated almost completely at the resting potential. The onset of inactivation was fastest at potentials negative to those that caused activation. When intracellular K+ was replaced by Cs+, large inward and outward currents were obtained that corresponded respectively to the above-mentioned DTX- and TEA-sensitive currents. Outward, TEA-sensitive current was carried by Cs+, with a PCs/PK of approximately 0.1. In current-clamped neurons, DTX induced repetitive firing and increased membrane time constant near rest but had little effect on action potential duration. These studies indicate that a low-threshold, DTX-sensitive current plays a key role in making NM neurons highly responsive to the onset and offset of synaptic stimuli.
鸡巨细胞核神经元外向电流的特性。《神经生理学杂志》80: 2824 - 2835, 1998年。巨细胞核（NM）的神经元通过多种电压门控和配体门控离子通道的汇聚来保留听觉信号的时间。为了更好地理解这些通道如何相互作用，我们对脑片中NM神经元外向电流的动力学、电压敏感性和药理学特性进行了表征。外向电流的反转电位（Erev）随钾离子浓度变化，这与钾离子携带的电流预期一致。然而，Erev始终比钾离子的能斯特电位（EK）更正。Erev偏离计算出的EK最可能是由于静息时和去极化步骤中活跃的钾离子电导使细胞外空间中钾离子积累所致。研究了三种外向钾电流，它们在电压和药理学敏感性方面有所不同。一种对四乙铵（TEA）敏感的高阈值电流在去极化开始后1 - 5毫秒内被激活，半最大激活电压（V1/2）为 - 19毫伏。它被4 - 氨基吡啶（4 - AP）部分阻断，是NM神经元的主要离子电导。一种对树突毒素 - I（DTX）和4 - AP敏感的低阈值电流的V1/2为 - 58毫伏，激活动力学迅速，且只有部分失活，衰减时间常数在20到100毫秒之间。观察到一种快速失活电流，它对TEA和DTX有抗性，并被细胞内的Cs +阻断。瞬态电流在静息电位时几乎完全失活。失活的起始在导致激活的电位的负值处最快。当细胞内的K +被Cs +取代时，获得了分别对应于上述对DTX和TEA敏感电流的大的内向和外向电流。外向的、对TEA敏感的电流由Cs +携带，PCs/PK约为0.1。在电流钳制的神经元中，DTX诱导重复放电并增加静息附近的膜时间常数，但对动作电位持续时间影响很小。这些研究表明，一种低阈值、对DTX敏感的电流在使NM神经元对突触刺激的起始和终止高度敏感方面起关键作用。
