Development of ionic currents underlying changes in action potential waveforms in rat spinal motoneurons
Development of ionic currents underlying changes in action potential waveforms in rat spinal motoneurons
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DOI：
10.1152/jn.1998.80.6.3047
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发表时间：
1998-12-01
影响因子：
2.5
通讯作者：
Ziskind-Conhaim, L
中科院分区：
文献类型：
--
作者：
Gao, BX;Ziskind-Conhaim, L
利用全细胞电压和电流钳记录研究了胚胎和出生后大鼠脊髓运动神经元动作电位特性变化的离子分化机制。在胚胎运动神经元中记录到相对缓慢上升，延长，主要依赖Na+的动作电位，并且在长时间的细胞内注射去极化电流时引发后去极化电位。动作电位幅值、上升率和复极率显著增加，出生后即出现明显的后超极化电位（AHP）。同时，长时间的电流注入引起了重复性动作电位放电。为了确定这些变化背后的离子机制，研究了电压门控宏观Na+、Ca2+和K+电流的性质。快速上升的Na+电流（I-Na）和缓慢上升的Ca2+电流（I-Ca）在胚胎发育早期表达，但只有INa是触发动作电位的必要和充分条件。出生后I-Na和I-Ca密度显著增加，而I-Na和I-Ca达到峰值的时间缩短。出生后I-Na升高导致动作电位超调，其上升速度明显快于出生前。研究了三种向外K+电流的特性：瞬态a型电流（I-A）、非灭活延迟整流器型电流（I-K）和Ca2+依赖性K+电流I-K（Ca）。出生后I-K和I-K（Ca）密度的两倍增加导致持续时间较短的动作电位和AHP的产生。相对较大的I-A在神经元发育早期表达，但与I-K和I-K（Ca）不同，其密度在出生后不增加。三种类型的K+通道对动作电位放电行为的调节作用相反：I-K和I-A增加动作电位放电速率，而I-K（Ca）降低动作电位放电速率。我们的研究结果表明，动作电位波形的发育变化和重复放电的发生与现有电压门控离子通道密度的大量增加有关，而不是与新通道类型的表达有关。
Differentiation of the ionic mechanism underlying changes in action potential properties was investigated in spinal motoneurons of embryonic and postnatal rats using whole cell voltage- and current-clamp recordings. Relatively slow-rising, prolonged, largely Na+-dependent action potentials were recorded in embryonic motoneurons, and afterdepolarizing potentials were elicited in response to prolonged intracellular injections of depolarizing currents. Action potential amplitude, as well as its rates of rise and repolarization significantly increased, and an afterhyperpolarizing potential (AHP) became apparent immediately after birth. Concurrently, repetitive action potential firing was elicited in response to a prolonged current injection. To determine the ionic mechanism underlying these changes, the properties of voltage-gated macroscopic Na+, Ca2+, and K+ currents were examined. Fast-rising Na+ currents (I-Na) and slow-rising Ca2+ currents (I-Ca) were expressed early in embryonic development, but only INa was necessary and sufficient to trigger an action potential. I-Na and I-Ca densities significantly increased while the time to peak I-Na and I-Ca decreased after birth. The postnatal increase in I-Na resulted in overshooting action potential with significantly faster rate of rise than that recorded before birth. Properties of three types of outward K+ currents were examined: transient type-A current (I-A), noninactivating delayed rectifier-type current (I-K), and Ca2+-dependent K+ current I-K(Ca). The twofold postnatal increase in I-K and I-K(Ca) densities resulted in shorter duration action potential and the generation of AHP. Relatively large I-A was expressed early in neuronal development, but unlike I-K and I-K(Ca) its density did not increase after birth. The three types of K+ channels had opposite modulatory actions on action potential firing behavior: I-K and I-A increased the firing rate, whereas I-K(Ca) decreased it. Our findings demonstrated that the developmental changes in action potential waveforms and the onset of repetitive firing were correlated with large increases in the densities ties of existing voltage-gated ion channels rather than the expression of new channel types.