The intrinsic electrophysiological characteristics of fly lobula plate tangential cells .2. Active membrane properties
The intrinsic electrophysiological characteristics of fly lobula plate tangential cells .2. Active membrane properties
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DOI：
10.1023/a:1008804117334
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发表时间：
1997-11-01
影响因子：
1.2
通讯作者：
Borst, A
中科院分区：
文献类型：
--
作者：
Haag, J;Theunissen, F;Borst, A
使用开关电极电压钳技术检查飞小叶板切向细胞中的电压门控电流。在 CH 细胞中，发现了两种电流（图 1、2）：缓慢的钙内向电流和延迟整流、非失活的钾外向电流。 HS 和 VS 细胞似乎具有与 CH 细胞相似的电流，但此外，还表现出快速激活的钠内向电流和钠激活的钾外向电流（图 3、4）。虽然所有三种细胞类别中的延迟整流钾电流负责先前描述的观察到的外向整流（Borst 和 Haag，1996），但钠内向电流产生在 HS 和 VS 细胞中发现的快速且不规则的尖峰状去极化，但在 CH 细胞中则不然：当钠电流被 TTX 或细胞内 QX314 阻断时，在电流钳条件下，HS 细胞中不再能引起动作电位（图 5）。正如在 HS 细胞中所证明的，空间钳条件足以抑制突触诱导的动作电位（图 6）。将上述电流与适当的特性合并到细胞的区室模型中（图 7，s）。这些细胞的解剖学和电无源膜参数在之前的论文中确定（Borst 和 Haag，1996）。将电流参数与电压钳数据拟合后（图 9），模型细胞定性地模拟了电流钳条件下飞切向细胞对电流注入的响应（图 10）。模拟表明，无论是在连续超极化过程中的被动模型还是主动模型中，HS 和 VS 细胞中观察到的电致密性在连续去极化期间的主动模型中显着下降（图 11）。主动 HS 模型再现了注入轴突的电流的频率依赖性放大（图 12）。
The voltage-gated currents in the fly lobula plate tangential cells were examined using the switched electrode voltage clamp technique. In CH cells, two currents were identified (Figs. 1, 2): a slow calcium inward current and a delayed rectifying, noninactivating potassium outward current. HS and VS cells appear to possess similar currents to CH cells, but in addition, exhibit a fast-activating sodium inward current and a sodium-activated potassium outward current (Figs. 3, 4). While the delayed rectifying potassium current in all three cell classes is responsible for the observed outward rectification described previously (Borst and Haag, 1996), the sodium inward current produces the fast and irregular spikelike depolarizations found in HS and VS cells but not in CH cells: When the sodium current is blocked by either TTX or intracellular QX314, no more action potentials can be elicited in HS cells under current-clamp conditions (Fig. 5). As is demonstrated in HS cells, space clamp conditions are sufficient to suppress synaptically induced action potentials (Fig. 6).The currents described above were incorporated with the appropriate characteristics into compartmental models of the cells (Figs. 7, s). The anatomical and electrically passive membrane parameters of these cells were determined in a preceding paper (Borst and Haag, 1996). After fitting the current parameters to the voltage-clamp data (Fig. 9), the model cells qualitatively mimicked the fly tangential cells under current clamp conditions in response to current injection (Fig. 10). The simulations demonstrated that the electrical compactness seen in the HS and VS cells, either in passive models or in active models during continuous hyperpolarization, decreased significantly in the active models during continuous depolarization (Fig. 11). Active HS models reproduce the frequency-dependent amplification of current injected into their axon (Fig. 12).