Stafstrom C E, Schwindt P C, Crill W E
J Neurophysiol. 1984 Aug;52(2):278-89. doi: 10.1152/jn.1984.52.2.278.
The passive cable properties of neurons from layer V of cat neocortex were studied in an in vitro slice preparation using current-clamp techniques and a single-microelectrode voltage clamp. Neurons were examined in the presence and absence of several agents that block time- and voltage-dependent conductances. The charging response to an injected current pulse was well fitted by a single exponential in 12 of 17 cells examined. By itself, this result would suggest that most of the neurons are isopotential. However, the existence of a nonisopotential region was demonstrated in all neurons examined using two alternative, independent methods: application of voltage-clamp steps and current impulses. The decay of the capacitive charging transient following a voltage-clamp step reflects charge redistribution solely in the nonisopotential region and had a mean time constant about 17% of the membrane time constant, tau m. The voltage decay following a current impulse was always fitted by (at least) two exponentials, the shorter of which was about 9% of tau m. These results suggest that a nonisopotential region exists but is electrotonically short, of relatively low-input conductance, or both, independent of a particular neuron model. Adopting Rall's (23, 24) idealized neuron model (isopotential compartment attached to a finite-length uniform cable) resulted in a mean value for the equivalent electrotonic length (L) of the nonisopotential compartment of 0.72 space constants from voltage-clamp data and 1.21 space constants from impulse-response data. A dendrite-to-soma conductance ratio (p) of 2-4 was obtained from either procedure. There were no significant differences in the cable parameters between normal cells and those where conductance-blocking agents were present. A specific membrane resistance (Rm) ranging from 2,300 to 11,700 omega X cm2 was estimated by assuming values of specific membrane capacitance reported in the literature. We conclude that large layer V neocortical neurons in vitro are electrotonically compact in the voltage range near resting potential and in the absence of significant tonic synaptic input. In this respect, their electrotonic cable properties resemble those of other mammalian neurons in vitro.
利用电流钳技术和单微电极电压钳，在体外脑片制备中研究了猫新皮层V层神经元的被动电缆特性。在存在和不存在几种阻断时间和电压依赖性电导的试剂的情况下对神经元进行了检查。在检查的17个细胞中的12个中，对注入电流脉冲的充电响应很好地拟合为单指数。就其本身而言，这个结果表明大多数神经元是等电位的。然而，使用两种替代的、独立的方法在所有检查的神经元中都证明了非等电位区域的存在：施加电压钳步阶和电流脉冲。电压钳步阶后电容性充电瞬变的衰减仅反映非等电位区域中的电荷重新分布，其平均时间常数约为膜时间常数tau m的17%。电流脉冲后的电压衰减总是（至少）由两个指数拟合，其中较短的约为tau m的9%。这些结果表明存在一个非等电位区域，但在电紧张方面较短，输入电导相对较低，或两者兼而有之，与特定的神经元模型无关。采用拉尔（23,24）的理想化神经元模型（连接到有限长度均匀电缆的等电位隔室），从电压钳数据得到非等电位隔室的等效电紧张长度（L）的平均值为0.72空间常数，从脉冲响应数据得到为1.21空间常数。通过这两种方法中的任何一种都得到树突与胞体电导比（p）为2至4。正常细胞和存在电导阻断剂的细胞之间的电缆参数没有显著差异。通过假设文献中报道的比膜电容值，估计比膜电阻（Rm）范围为2300至11700Ω×cm2。我们得出结论，体外培养的大的新皮层V层神经元在静息电位附近的电压范围内且在没有显著强直突触输入的情况下在电紧张方面是紧密的。在这方面，它们的电紧张电缆特性类似于体外培养的其他哺乳动物神经元。
