There were two kinds of main K⁺ current components for DRG neuron, including rectifier potassium current (I_K) and transient outward potassium current (I_A). TEA was used as specificity blocking agent to delay rectifier K⁺ current while IC₅₀ of inhibiting effect was in the range of 0.2~100mM. In our study, 20mM of TEA was selected. The results of research on molecular biology showed that three kinds of A-type K-channel of different genetic code included Kv1.4, Kv3.4 and Kv4.2 ^[19]. Moreover, Kv3.4 channel was highly-sensitive with TEA (IC₅₀=0.3mM) ^[20-21], so it was impossible to be expressed on DRG cell of this study. On the contrary, the features of the current of Kv1.4 and Kv4.2 channels were highly similar with the features of the observed DRG neuron I_A. The research of immunocytochemistry discovered that protein of Kv4.2 channel was located at dendrite and cell body of neuron, while the protein of Kv1.4 was located at axon ^[22], so that the channel on cell body of DRG neuron observed by us might be A-type channel expressed by Kv4.2 genetic.

The activation and inactivation curves of I_A shifted to the right by La³⁺, Gd³⁺ and Yb³⁺ , etc. with concentration of 100μmol/L, and the degree of shifting displayed upward tendency. It had been known that diameter of the three rare-earth ion decreased gradually, it represented that the rare-earth ion with smaller diameter might be easier to cause activation as well as to shift to the right of I_A, it also might inhibit I_A and decrease the voltage sensitivity of I_A channel, too. For rare-earth ion outside the cell, its influence on protein of Kv4.2 channel increased as the diameter of ion decreased. Lots of research reported that I_A was important for repetitive discharge of neuronal action potential ^[23-24]. I_A of DRG could adjust the time for repetitively discharging excitability, the repolarization of each action potential as well as the time for action potential to achieve discharging threshold. As I_A had a series of importance on excitability of neuron, the inhibition of I_A was very important for hyperexcitability of neuron when we studied the function of Ln³⁺. When the potential of membrane was depolarized, Ln³⁺ might inhibit I_A and improved the excitability as well as discharged frequent of DRG. Ln³⁺ also influenced the general feeling physiology characteristics of DRG neuron which might lead to abnormal discharging characteristics. Moreover, it accelerated the consumption of energy, and Na⁺- Ca²⁺ pump on membrane could not convey Ca²⁺ to extracellular cell because of malfunction ^[25].

 

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DRG神经元上有两种主要的K⁺电流成分，延迟整流K⁺电流（I_K）和瞬间外向K⁺电流（I_A）。TEA，作为延迟整流K⁺电流的特异性阻断剂，其抑制效应的IC₅₀的范围在0.2~100mM之间，实验中我们选择20mM TEA。分子生物学研究结果显示不同基因编码的三种A-型K通道有Kv1.4, Kv3.4和Kv4.2 ^[19]。而Kv3.4通道对TEA高度敏感（IC₅₀=0.3 mM）^[20-21], 因而不可能在本研究中的DRG细胞上表达。相反，Kv1.4和Kv4.2通道电流的特性与本研究中观察到的DRG神经元I_A的特性十分吻合。免疫细胞化学研究发现Kv4.2通道蛋白位于神经元的树突和胞体，而Kv1.4蛋白位于轴突^[22]，因此我们在DRG神经元胞体上观察的很可能是Kv4.2基因表达的A-型通道。

100μmol/L La³⁺,Gd³⁺,Yb³⁺使I_A激活和失活曲线均向右移动，右移的程度呈增长趋势。我们知道这三种稀土离子的半径呈递减趋势，说明半径越小的稀土离子使I_A的激活和失活右移的程度越大，抑制I_A的程度越大，使I_A通道的电压敏感性大大减弱。胞外的稀土离子随着离子半径的减小，影响Kv4.2通道蛋白的程度就越大。大量的研究认为I_A对于各种神经元的动作电位的重复发放有重要作用^[23-24]，DRG中的I_A调节兴奋重复发放的时程，单个动作电位的复极化，以及到达动作电位发放阈值的时间。由于I_A对于神经元兴奋性所具有的一系列重要作用，我们研究在Ln³⁺作用时，I_A受到抑制对于DRG的超兴奋性则具有重要意义。当膜电位去极化时，Ln³⁺抑制I_A并因此增加了神经元的兴奋性和发放频率。Ln³⁺使DRG神经元的一般感觉生理特性受到影响，可能导致异常的发放特性，加速能量的消耗，使膜上的Na⁺- Ca²⁺泵因功能失常而不能向胞外转运Ca^{2 + [25]}。

 

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