Walden J, Speckmann E J, Witte O W
Institut für Physiologie/Bereich Neurophysiologie der Universität, Münster, F.R.G.
Brain Res. 1988 Nov 15;473(2):294-305. doi: 10.1016/0006-8993(88)90858-x.
After systemic application of pentylenetetrazol (PTZ), mammalian as well as molluscan neurons generate epileptic paroxysmal depolarization shifts. For a further analysis of these potential oscillations the membrane currents induced by local application of PTZ onto identified neurons of Helix pomatia were investigated. Different types of responses were obtained at membrane potentials negative and positive to ca. -30 mV. At holding potentials more negative than -30 mV, PTZ as a rule evoked an inward current, sometimes preceded by a brief outward current. In a few experiments only a solitary outward current was found. The amplitudes of the inward and outward currents increased towards more negative potentials. The inward current was associated with a decrease and the outward current with an increase in membrane resistance. Besides these findings pharmacological and ion substitution experiments indicate that the inward current represents an unspecific current. At holding potentials more positive than -30 mV, PTZ evoked a sequence of currents which was the same in all neurons. This stereotyped current sequence consisted of (i) an early inward current, (ii) an intermediate outward current, and (iii) a late long-lasting inward current. The amplitudes of all these components increased towards more positive potentials with the outward current being particularly enhanced. The early inward current and the following outward current were associated with a decrease and the late inward current with an increase of the membrane resistance. Besides these pharmacological and ion substitution experiments suggest that the early inward current represents a mixed sodium and calcium current, the intermediate outward current a calcium activated potassium current. The late inward current is assumed to be due to a decreased potassium conductance. On the basis of the present results, it may be concluded that the unspecific inward current in the negative potential range is involved in the initiation and the calcium dependent potassium current in the termination of spontaneously occurring paroxysmal depolarization shifts.
全身应用戊四氮（PTZ）后，哺乳动物以及软体动物的神经元会产生癫痫性阵发性去极化偏移。为了进一步分析这些潜在的振荡，研究了将PTZ局部应用于苹果螺已鉴定神经元时所诱发的膜电流。在膜电位负于约-30 mV和正于约-30 mV时获得了不同类型的反应。在保持电位比-30 mV更负时，PTZ通常诱发内向电流，有时之前会有短暂的外向电流。在少数实验中仅发现了单个外向电流。内向和外向电流的幅度向更负的电位增加。内向电流与膜电阻降低相关，外向电流与膜电阻增加相关。除了这些发现外，药理学和离子替代实验表明内向电流代表非特异性电流。在保持电位比-30 mV更正时，PTZ诱发了一系列在所有神经元中都相同的电流。这个刻板的电流序列包括：（i）早期内向电流，（ii）中间外向电流，以及（iii）晚期持久内向电流。所有这些成分的幅度向更正的电位增加，其中外向电流增加尤为明显。早期内向电流和随后的外向电流与膜电阻降低相关，晚期内向电流与膜电阻增加相关。此外，这些药理学和离子替代实验表明早期内向电流代表钠和钙混合电流，中间外向电流代表钙激活钾电流。晚期内向电流被认为是由于钾电导降低所致。根据目前的结果，可以得出结论，负电位范围内的非特异性内向电流参与了自发发生的阵发性去极化偏移的起始，而钙依赖性钾电流参与了其终止。
