EFFECTS OF ELECTRIC-FIELDS ON TRANSMEMBRANE POTENTIAL AND EXCITABILITY OF TURTLE CEREBELLAR PURKINJE-CELLS INVITRO
EFFECTS OF ELECTRIC-FIELDS ON TRANSMEMBRANE POTENTIAL AND EXCITABILITY OF TURTLE CEREBELLAR PURKINJE-CELLS INVITRO
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DOI：
10.1113/jphysiol.1988.sp017232
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发表时间：
1988-08-01
影响因子：
5.5
通讯作者：
NICHOLSON, C
中科院分区：
文献类型：
--
作者：
CHAN, CY;HOUNSGAARD, J;NICHOLSON, C
1.用细胞内和细胞外同步记录的方法，连续测定了甲鱼小脑浦肯野细胞(PC)对外加沿树突轴方向准稳态电场的跨膜电位(TMP)反应。TMP是从小脑相同深度记录的细胞内电位减去细胞外电压场得到的。2.外加电场改变了TMP，其极性和幅度与PC膜上的位置有关。在一个给定的位置，这种响应随着外场的线性增加而增加，直到一个阈值水平，超过这个阈值，就会出现主动响应。3.TMP的基本效应是场指向的那一半枝晶的去极化和另一半的超极化。汇集的TMP深度剖面显示，从分子层的中间到两端，极化稳步增加。这一分布与以前提出的电缆模型的预测结果相关联，首次为它们提供了经验支持。4.场致去极化可触发主动反应。河豚毒素(TTX)敏感的动作电位出现在体细胞区域的初级去极化过程中。切迹的钙离子依赖的动作电位在远端和中树突区出现初级去极化。5.TMP近端去极化可触发TTX敏感电压平台。反过来，激活了Na+-尖峰电流序列。放电频率与外场成正比。在约160个峰/S时，Na+峰失活，而TMP水平上升到一个更去极化的平台。后一个平台也是TTX敏感的。6.在远端树突区去极化过程中，有时观察到钙依赖平台。这似乎与电导的小幅增加有关。7.场致超极化可抑制局部峰电位和电压平台，但在近端出现幅度降低的远端钙峰。同样，在远端区域，观察到低幅度、远距离的Na+峰和一个Na+平台叠加在超极化基线上。Na+平台对远端树突膜电流的分流无明显作用。8.动作电位的相位特征与我们在细胞外研究中注意到的调制模式相关(Chan和Nicholson，1986)。因此，细胞外单位(“巨峰”)可能是在胞体内激活并向远端扩散的Na+峰。有时，具有较高阈值的钙尖峰也可能被激活，以产生双时相反应。电压平台可能是观察到的一些爆发模式背后的机制。9.外场作用引起的这些主动反应的特征与通过微电极注入海龟PC(Hounsgaard and Midtgaard，1988)和豚鼠PC(Llinas and Sugimori，1980 a，b)的电流阶跃非常相似，证实了外场作为一种新的膜电生理工具的有效性。当细胞内电流注入和外场同时作用时，它们的作用是相加的。
1. Transmembrane potential (TMP)responses of Purkinje cells (PCs) in isolated turtle cerebellum to externally applied quasi-steady-state electric fields aligned with the dendritic axis were continuously measured using simultaneous intracellular and extracellular recording. TMP was obtained by subtraction of extracellular voltage fields from intracellular potential recorded at the same depth in the cerebellum. 2. The applied field changed the TMP with the polarity and amplitude dependent on the location on the PC membrane. This response at a given location increased linearly with external field up to a threshold level, beyond which active responses appeared. 3. The basic effect on TMP consisted of depolarization in the half of the dendrite towards which the fields were directed, and hyperpolarization in the other half. A pooled TMP depth-profile shows a steady increase in polarization from the middle of the molecular layer towards each end. This profile correlates with that predicted from previously proposed cable models, giving them empirical support for the first time. 4. Active responses were triggered by the field-induced depolarization. Tetrodotoxin (TTX)-sensitive action potentials arose with the primary depolarization in the somatic region. Notched, Ca2+-dependent action potentials arose with primary depolarization in the distal and mid-dendritic regions. 5. A TTX-sensitive voltage plateau was triggered by TMP-depolarization in the proximal region. In turn activated Na+-spike trains. The frequency of spiking was proportional to the external field. At around 160 spikes/s, the Na+spikes inactivated, and the TMP level rose to a more depolarized plateau. This latter plateau was also TTX-sensitive. 6. During depolarization of the distal dendritic region, sometimes a Ca2+-dependent plateau was observed. It appears to be associated with a small conductance increase. 7. Field-induced hyperpolarization suppressed local spiking and voltage plateaux, but remote Ca2+ spikes with reduced amplitude appeared in recordings from the proximal region. Similarly, in the distal region, low-amplitude, remote Na+ spikes and a Na+ plateau were observed superimposed on the hyperpolarizing baseline. The Na+ plateau apparently did not contribute to shunting of membrane currents in the distal dendrite. 8. The phase characteristics of the action potentials correlate with the modulation pattern noted in our extracellular study (Chan and Nicholson, 1986). Thus, the extracellular units (''giant spikes'') were probably Na+ spikes activated in the soma and spread distally. Occasionally Ca2+ spikes, with a higher threshold, might also be activated to give a dual-phase response. The voltage plateaux were probably the mechanism underlying some of the burst patterns observed. 9. The characteristics of these active responses elicited by external field application were very similar to those elicited by current steps injected via a microelectrode into turtle PCs (Hounsgaard and Midtgaard, 1988) and guinea-pig PCs (Llinas and Sugimori, 1980 a,b), confirming the effectiveness of external field as a novel membrane electrophysiological tool. When both intracellular current injection and external field were applied simultaneously, their effects were shown to be additive.