Kim H C, Chung M K
Department of Oral Physiology and Institute of Oral Biology, School of Dentistry, Seoul 130-701, Korea.
J Neurophysiol. 1999 Mar;81(3):1123-34. doi: 10.1152/jn.1999.81.3.1123.
Voltage-dependent sodium (INa) and calcium (ICa) currents in small (<30 microM) neurons from adult rat trigeminal root ganglia were characterized with a standard whole cell patch-clamp technique. Two types of INa showing different sensitivity to tetrodotoxin (TTX) were recorded, which showed marked differences in their activating and inactivating time courses. The activation and the steady-state inactivation kinetics of TTX-resistant INa were more depolarized by about +20 and +30 mV, respectively, than those of TTX-sensitive INa. Voltage-dependent ICa was recorded under the condition that suppressed sodium and potassium currents with 10 mM Ca2+ as a charge carrier. Depolarizing step pulses from a holding potential of -80 mV evoked two distinct inward ICa, low-voltage activated (LVA) and high-voltage activated (HVA) ICa. LVA ICa was first observed at -60 to -50 mV and reached a peak at about -30 mV. Amiloride (0.5 mM) suppressed approximately 60% of the LVA ICa, whereas approximately 10% of HVA ICa was inhibited by the same concentration of the amiloride. LVA ICa was far less affected by the presence of external Cd2+ or the replacement of Ca2+ by 10 Ba2+ than HVA ICa. The omega-conotoxin GVIA (omega-CgTx), an N-type ICa blocker, suppressed approximately 65% of the whole cell HVA ICa at the concentration of 1 microM. The omega-CgTx-resistant HVA ICa was sensitive to nifedipine (10 microM), a dihydropyridine (DHP) calcium channel antagonist, which produced an additional blockade by approximately 25% of the drug-free control ( approximately 70% of the omega-CgTx-resistant ICa). The combination of 10 microM nifedipine and 1 microM omega-CgTx left approximately 13% of the drug-free control ICa unblocked. The DHP agonist S(-)-BayK8644 (5 microM) shifted the activation of the HVA ICa to more negative potentials and increased its maximal amplitude. Additionally, S(-)-BayK8644 caused the appearance of a slowed component of the tail current. These results clearly demonstrate that the presence of two types of sodium channels, TTX sensitive and resistant, and three types of calcium channels, T, L, and N type, in the small-sized adult rat trigeminal ganglion neurons.
采用标准的全细胞膜片钳技术，对成年大鼠三叉神经节中小（<30微摩尔）神经元的电压依赖性钠电流（INa）和钙电流（ICa）进行了表征。记录到两种对河豚毒素（TTX）敏感性不同的INa，它们在激活和失活时间进程上表现出明显差异。与TTX敏感性INa相比，TTX抗性INa的激活和稳态失活动力学分别向更正电位方向移动约+20和+30毫伏。在以10毫摩尔Ca2+作为电荷载体抑制钠电流和钾电流的条件下记录电压依赖性ICa。从-80毫伏的 holding 电位进行去极化阶跃脉冲诱发了两种不同的内向ICa，即低电压激活（LVA）和高电压激活（HVA）ICa。LVA ICa首先在-60至-50毫伏时被观察到，并在约-30毫伏时达到峰值。氨氯地平（0.5毫摩尔）抑制了约60%的LVA ICa，而相同浓度的氨氯地平仅抑制了约10%的HVA ICa。与HVA ICa相比，LVA ICa受细胞外Cd2+存在或用10 Ba2+替代Ca2+的影响要小得多。ω-芋螺毒素GVIA（ω-CgTx），一种N型ICa阻滞剂，在1微摩尔浓度下抑制了约65%的全细胞HVA ICa。ω-CgTx抗性HVA ICa对硝苯地平（10微摩尔）敏感，硝苯地平是一种二氢吡啶（DHP）钙通道拮抗剂，它额外阻断了约25%的无药对照组电流（约70%的ω-CgTx抗性ICa）。10微摩尔硝苯地平和1微摩尔ω-CgTx的组合使约13%的无药对照组ICa未被阻断。DHP激动剂S(-)-BayK8644（5微摩尔）将HVA ICa的激活电位向更负电位方向移动，并增加了其最大幅度。此外，S(-)-BayK8644导致尾电流出现一个减慢的成分。这些结果清楚地表明，成年大鼠小型三叉神经节神经元中存在两种类型的钠通道，即TTX敏感型和抗性型，以及三种类型的钙通道，即T型、L型和N型。
