Membrane currents in visually identified motoneurones of neonatal rat spinal cord.
Membrane currents in visually identified motoneurones of neonatal rat spinal cord.
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新生大鼠脊髓视觉识别运动神经元的膜电流。
DOI：
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发表时间：
1990
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影响因子：
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通讯作者：
Tomoyuki Takahashi
中科院分区：
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作者：
Tomoyuki Takahashi
1.通过新生大鼠腰脊髓薄片的紧密密封全细胞记录来分析由运动神经元去极化引起的离子电流。通过使用荧光染料伊文思蓝进行逆行标记，证实了在诺马斯基光学下观察到的运动神经元的识别。 2. 在全细胞电压钳下，约 ‐70 mV 保持电位的去极化命令脉冲引起快速内向电流，随后出现外向电流。前者可以通过降低外部 Na+ 浓度或使用河豚毒素 (TTX) 来抑制。 TTX 的表观解离常数约为 13 nM。 3. TTX 应用后剩余的外向电流被 ‐50 mV 以上的去极化激活，在电流-电压关系中显示出明显的外向整流。根据外部和移液器 K+ 浓度计算，在 K+ 平衡电位附近，向外尾电流极性反转。 4、当外部Ca2+被Mg2+取代时，外向K+电流被显着且可逆地抑制。将不含 Ca2+ 的 Mg2+ 溶液中记录的电流与对照溶液中记录的电流相减，发现 Ca2(+) 依赖性 K+ 电流 IK(Ca) 具有瞬态 IC 和持续分量 IAHP；它的尾电流持续了数百毫秒。 5. 在无 Ca2(+)-Mg2+ 溶液中观察到的持续外向电流在很大程度上被外部施加氯化四乙铵 (30 mM) 所抑制，这表明它主要是延迟整流电流 IK。在含有 TEA 和 TTX 的无 Ca2(+)-Mg2+ 溶液中，观察到另一种瞬态外向电流，该电流通过以时间和电压依赖的方式去极化预脉冲而失活。稳态失活曲线表明在约 ‐77 mV 时有 50% 失活。 4-氨基吡啶（4-AP，4 mM）在很大程度上可逆地抑制该电流，而它不影响在不存在 TEA 的情况下观察到的 IK。建议瞬态向外电流对应于 A 电流 (IA)。 6. 在电流钳模式下记录动作电位。用 Mg2+ 替代外部 Ca2+ 显着减少了后超极化。与此同时，动作电位的复极相稍微延长。在无 Ca2(+)-Mg2+ 溶液中，4-AP 的应用显着延长了动作电位复极化。在含有 4-AP 的无 Ca2(+)-Mg2+ 溶液中，添加 TEA-Cl 进一步延长了动作电位的持续时间。结论是三种不同的钾电流IC、IA和IK可能都有助于大鼠脊髓运动神经元的动作电位复极化。
1. Ionic currents induced by depolarization of motoneurones were analysed by tight‐seal, whole‐cell recording in thin slices of neonatal rat lumbar spinal cord. Identification of motoneurones viewed under Nomarski optics was confirmed by retrograde labelling with the fluorescent dye, Evans Blue. 2. Under whole‐cell voltage clamp, depolarizing command pulses from a holding potential of about ‐70 mV evoked a fast inward current followed by an outward current. The former was suppressed either by lowering external Na+ concentration or by application of tetrodotoxin (TTX). The apparent dissociation constant of TTX was about 13 nM. 3. The outward current remaining after TTX application was activated by depolarization above ‐50 mV, showing marked outward rectification in the current‐voltage relation. Outward tail currents reversed in polarity near the K+ equilibrium potential calculated from the external and pipette K+ concentrations. 4. When external Ca2+ was replaced by Mg2+, the outward K+ current was suppressed markedly and reversibly. Subtraction of current recorded in Ca2+‐free‐Mg2+ solution from that in control solution revealed a Ca2(+)‐dependent K+ current, IK(Ca) with both a transient, IC, and a sustained component IAHP; its tail current lasted for several hundred milliseconds. 5. The sustained outward current observed in Ca2(+)‐free‐Mg2+ solution was largely suppressed by external application of tetraethylammonium chloride (30 mM), suggesting that it was mostly the delayed rectifier current, IK. In Ca2(+)‐free‐Mg2+ solution containing TEA and TTX, another transient outward current was observed, which was inactivated by depolarizing pre‐pulses in a time‐ and voltage‐dependent manner. The steady‐state inactivation curve indicated 50% inactivation at about ‐77 mV. 4‐Aminopyridine (4‐AP, 4 mM) largely and reversibly suppressed this current, whereas it did not affect IK observed in the absence of TEA. It is suggested that the transient outward current corresponds to the A‐current (IA). 6. Action potentials were recorded in current‐clamp mode. Replacement of external Ca2+ by Mg2+ markedly diminished the after‐hyperpolarization. Concomitantly, the repolarizing phase of action potentials was slightly prolonged. In Ca2(+)‐free‐Mg2+ solution, application of 4‐AP markedly prolonged action potential repolarization. In Ca2(+)‐free‐Mg2+ solution containing 4‐AP, addition of TEA‐Cl further prolonged the duration of the action potential. It is concluded that three different potassium currents, IC, IA and IK may all contribute to action potential repolarization in rat spinal motoneurones.