CHARACTERIZATION OF TTX-SENSITIVE AND TTX-RESISTANT SODIUM CURRENTS IN SMALL-CELLS FROM ADULT-RAT DORSAL-ROOT GANGLIA
CHARACTERIZATION OF TTX-SENSITIVE AND TTX-RESISTANT SODIUM CURRENTS IN SMALL-CELLS FROM ADULT-RAT DORSAL-ROOT GANGLIA
复制标题
DOI：
10.1113/jphysiol.1993.sp019583
复制
发表时间：
1993-04-01
影响因子：
5.5
通讯作者：
ELLIOTT, JR
中科院分区：
文献类型：
--
作者：
ELLIOTT, AA;ELLIOTT, JR
1. 采用全细胞膜片钳技术研究室温下从成年大鼠分离并培养过夜的小直径（13-25 muM）背根神经节（DRG）细胞记录的两种钠电流（I(Na)）的特征。2.钠电流在药理学上被分离。内部 Cs+ 和外部四乙铵 (TEA) 离子用于抑制钾电流。使用内部EGTA、内部F-、低浓度(10μM)外部Ca2+和相对高浓度(5mm)内部和外部Mg2+的组合来阻断钙通道。剩余的电压相关电流在计算的钠平衡电位处反转方向。电流的反转电位和幅度都表现出对外部钠浓度的预期依赖性。3． I(Na) 亚型最初的特征是对河豚毒素 (TTX) 的敏感性。 0.1 μM TTX 可以抑制 TTX 敏感 (TTX(s)) 电流至少 97%。在 0.3 muM TTX 存在下记录了 TTX 抗性 (TTX(r)) I(Na)，并且在 75 muM TTX 中振幅似乎降低了不到 50% (n = 1).4。与早期研究一样，发现 TTX(r) I(Na) 的电流-电压关系峰值、归一化电导曲线的中点以及稳态失活参数 (h(无穷大)) 为 0.5 时的电势 (V(h)) 显着更加去极化（分别约为 10、14 和 37 mV）。归一化电导曲线中点的斜率几乎没有差异（TTX(s) I(Na) 电流的平均斜率因子为 5.1 mV，TTX(r) 电流的平均斜率因子为 4.9 mV），但 TTX(r) 电流的 h（无穷大）曲线明显比 TTX(s) 电流的曲线陡峭（平均斜率因子分别为 3.8 和 11.5 mV）。 TTX(r) I(Na) 的峰值时间和从保持电位 - 67 mV 记录的峰值电流的衰减时间常数均比 TTX(s) 电流慢三倍以上。5。然而，与激活和衰变动力学的差异形成鲜明对比的是，“慢速”TTX(r) I(Na) 在 - 67 mV 时从失活中恢复或重新启动，比“快速”TTX(s) I(Na) 快十倍以上。6。 TTX(s) 和 TTX(r) I(Na) 在 - 67 mV 下的重新启动动力学和峰值 I(Na) 的衰减阶段动力学中明显的差异在很大程度上可以用其各自失活系统的电压依赖性来解释。7。将讨论两种钠通道亚型的失活系统（静息失活和重新启动动力学）的电压依赖性如此大的差异对 DRG 细胞可能的根本重要性。
1. The whole-cell patch-clamp technique was used to investigate the characteristics of two types of sodium current (I(Na)) recorded at room temperature from small diameter (13-25 muM) dorsal root ganglion (DRG) cells, isolated from adult rats and maintained overnight in culture.2. Sodium currents were isolated pharmacologically. Internal Cs+ and external tetraethylammonium (TEA) ions were used to suppress potassium currents. A combination of internal EGTA, internal F-, a low (10 muM) concentration of external Ca2+ and a relatively high (5 mm) concentration of internal and external Mg2+ was used to block calcium channels. The remaining voltage-dependent currents reversed direction at the calculated sodium equilibrium potential. Both the reversal potential and magnitude of the currents exhibited the expected dependence on the external sodium concentration.3. I(Na) subtypes were characterized initially in terms of their sensitivity to tetrodotoxin (TTX). TTX-sensitive (TTX(s)) currents were at least 97 % suppressed by 0.1 muM TTX. TTX-resistant (TTX(r)) I(Na) were recorded in the presence of 0.3 muM TTX and appeared to be reduced in amplitude by less than 50 % in 75 muM TTX (n = 1).4. As in earlier studies, the peak of the current-voltage relationship, the mid-point of the normalized conductance curve and the potential (V(h)) at which the steady-state inactivation parameter (h(infinity)) was 0.5 were found to be significantly more depolarized for the TTX(r) I(Na) (by ca 10, 14 and 37 mV respectively). There was little difference in the slope at the mid-point of the normalized conductance curves (the mean slope factors were 5.1 mV for the TTX(s) I(Na) and 4.9 mV for the TTX(r) current) but the h(infinity) curves for TTX(r) currents were significantly steeper than those for TTX(s) currents (mean slope factors of 3.8 and 11.5 mV respectively). Both the time to peak and the decay time constant of the peak current recorded from a holding potential of - 67 mV were more than a factor of three slower for the TTX(r) I(Na) than for the TTX(s) current.5. However, in direct contrast to the difference in activation and decay kinetics, 'slow' TTX(r) I(Na) recovered from inactivation at - 67 mV, or reprimed, more than a factor of ten faster than 'fast' TTX(s) I(Na).6. The differences apparent in both the repriming kinetics of TTX(s) and TTX(r) I(Na) at - 67 mV and the kinetics of the decay phase of the peak I(Na) are shown to be explicable largely in terms of the voltage dependence of their respective inactivation systems.7. The possible fundamental importance to DRG cells of such large differences in the voltage dependence of the inactivation systems (both resting inactivation and repriming kinetics) of the two sodium channel subtypes will be discussed.