Baker M D, Bostock H
Sobell Department of Neurophysiology, Institute of Neurology, London, United Kingdom.
J Neurophysiol. 1997 Mar;77(3):1503-13. doi: 10.1152/jn.1997.77.3.1503.
Dorsal root ganglion neurons from adult rats (> or = 200 g) were maintained in culture for between 1 and 3 days. Membrane currents generated by large neurons (50-75 microns apparent diameter) were recorded with the whole cell patch-clamp technique. Large neurons generated transient Na+ currents and at least two types of inward current that persisted throughout 200-ms voltage-clamp steps to +20 mV. One persistent current activated close to -35 mV (high threshold), whereas in about half of the cells another persistent current began to activate negative to -70 mV (low threshold). The high-threshold persistent current was identified as a Ca2+ current, as previously described in these neurons. The low-threshold current was reversibly suppressed either by replacing external Na+ with tetramethylammonium ions or by reducing external Na+ concentration ([Na+]) and simultaneously raising external [Ca2+]. It was blocked by tetrodotoxin (TTX) with an apparent equilibrium dissociation constant in the single nanomolar range. We conclude that the low-threshold current is a TTX-sensitive, persistent Na+ current. The persistent TTX-sensitive current contributed to steady-state membrane current from at least -70 mV to 0 mV, a wider potential range than predicted by activation-inactivation gating overlap for transient Na+ current. Because of its low threshold and fast activation kinetics, the persistent Na+ current is expected to play an important role in determining membrane excitability.
取自成年大鼠（体重≥200克）的背根神经节神经元在培养皿中培养1至3天。用全细胞膜片钳技术记录大神经元（表观直径50 - 75微米）产生的膜电流。大神经元产生瞬时钠电流以及至少两种类型的内向电流，这些内向电流在200毫秒电压钳制至+20毫伏的过程中持续存在。一种持续电流在接近 - 35毫伏时激活（高阈值），而在大约一半的细胞中，另一种持续电流在负于 - 70毫伏时开始激活（低阈值）。如先前在这些神经元中所描述的，高阈值持续电流被确定为钙电流。低阈值电流可通过用四甲基铵离子替代细胞外钠离子或通过降低细胞外钠离子浓度（[Na⁺]）并同时提高细胞外[Ca²⁺]浓度而被可逆性抑制。它被河豚毒素（TTX）阻断，表观平衡解离常数在单纳摩尔范围内。我们得出结论，低阈值电流是一种对TTX敏感的持续钠电流。这种持续的对TTX敏感的电流对至少从 - 70毫伏到0毫伏的稳态膜电流有贡献，这一电位范围比瞬时钠电流的激活 - 失活门控重叠所预测的范围更宽。由于其低阈值和快速激活动力学，持续钠电流预计在决定膜兴奋性方面起重要作用。
