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双蔗糖间隙中多纤维束的电压钳模拟:电缆复杂性

Voltage clamp simulations for multifiber bundles in a double sucrose gap: cable complications.

作者信息

Solchenbach K, Haas H G, Brommundt G

出版信息

Gen Physiol Biophys. 1986 Oct;5(5):449-71.

PMID:2433182
Abstract

A theoretical model is presented for voltage clamp of a bundle of cylindrical excitable cells in a double sucrose gap. The preparation in the test node is represented by a single one-dimensional cable (length/diameter ratio approximately) with standard Hodgkin-Huxley kinetics for transmembrane Na current. Imperfections of voltage control due to internal (longitudinal) resistivity and external (radial) resistance in series to the membrane are analysed. The electrical behavior of a fiber is described by the cable equation with appropriate boundary conditions and subsidiary equations reflecting the membrane characteristics. Membrane voltage and current distribution in response to a step command was obtained by numerical integration. The results are described in two papers. The present paper deals with the effect of internal resistivity with the external resistance being neglected. The closed loop response of a fiber displays a strong tendency to oscillate. To stabilize the system a phase lead was inserted and the gain of the control amplifier was reduced. Conditions for stability were examined by Nyquist analysis. When the Na system was activated by a command pulse below ENa, a voltage gradient developed between a depolarization (relative to the command signal) at the end where voltage was monitored and a hyperpolarization at the site of current injection. In spite of a poor voltage control the total measured current appeared to have a smooth transient. With large voltage gradients a small, second inward current was seen. At a low (high) Na conductance maximum peak inward current was larger (smaller) that the current expected from ideal space clamping.

摘要

提出了一种用于双蔗糖间隙中一束圆柱形可兴奋细胞电压钳制的理论模型。测试节点中的标本由一根一维电缆(长度/直径比约为)表示,其跨膜钠电流具有标准的霍奇金-赫胥黎动力学。分析了由于与膜串联的内部(纵向)电阻率和外部(径向)电阻导致的电压控制不完善情况。纤维的电学行为由具有适当边界条件和反映膜特性的辅助方程的电缆方程描述。通过数值积分获得了响应阶跃指令的膜电压和电流分布。结果在两篇论文中进行了描述。本文讨论了忽略外部电阻时内部电阻率的影响。纤维的闭环响应显示出强烈的振荡趋势。为了稳定系统,插入了一个超前相位并降低了控制放大器的增益。通过奈奎斯特分析研究了稳定性条件。当钠系统由低于ENa的指令脉冲激活时,在监测电压的一端的去极化(相对于指令信号)与电流注入部位的超极化之间会形成电压梯度。尽管电压控制不佳,但测得的总电流似乎具有平滑的瞬态。在大电压梯度下,可以看到一个小的二次内向电流。在低(高)钠电导时,最大峰值内向电流大于(小于)理想空间钳制预期的电流。

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