Ramón F, Anderson N, Joyner R W, Moore J W
Biophys J. 1975 Jan;15(1):55-69. doi: 10.1016/S0006-3495(75)85791-2.
In this paper we extend the simulation of the voltage clamp of a single nerve fiber to a bundle of axons. These simulations included not only the description of the voltage clamp circuit and a single unidimensional cable to represent the preparation in the "node" region of a double sucrose gap used previously but also a series resistance and a shunt pathway. The output of the voltage control amplifier is applied across the membrane plus the series resistance, producing a voltage drop across the series resistance due to the current generated by the membrane in response to a depolarizing voltage step. Since the membrane current has an inward and an outward phase, voltage drops of opposite sign are produced across the series resistance. During the transient current and at all points along an axon, the potential deviation produced by the series resistance is opposite to the deviation produced by the longitudinal gradient. Only at a command potential equal to the sodium equilibrium potential, the membrane potential transiently matches the command potential. For the attempted voltage clamp of an axon, values of series resistance larger than 50 omega-cm2 allowed propagated action potentials in the membrane. In spite of the presence of propagated action potentials at the calbe membrane, the recorded current does not show "notches" and it has a phase of inward current and a phase of outward current. It is concluded that, in a multicellular preparation with series resistance, the recording of a square voltage pulse does not indicate voltage control of the transmembrane potential. The presence of a shunt pathway produces inaccurate values of current density. Neither series or shunt resistance produce "notches" in the current records.
在本文中，我们将单个神经纤维电压钳的模拟扩展到一束轴突。这些模拟不仅包括对电压钳电路的描述以及用一根一维电缆来表示先前使用的双蔗糖间隙“节点”区域中的标本，还包括一个串联电阻和一条并联通路。电压控制放大器的输出施加在膜加上串联电阻两端，由于膜在去极化电压阶跃响应中产生的电流，会在串联电阻上产生一个电压降。由于膜电流有内向和外向两个阶段，所以在串联电阻上会产生符号相反的电压降。在瞬态电流期间以及沿着轴突的所有点，串联电阻产生的电位偏差与纵向梯度产生的偏差方向相反。只有在指令电位等于钠平衡电位时，膜电位才会短暂地与指令电位匹配。对于试图对轴突进行电压钳制的情况，串联电阻值大于50Ω·cm²时会使膜中出现传播的动作电位。尽管电缆膜上存在传播的动作电位，但记录到的电流并未显示“缺口”，且有内向电流阶段和外向电流阶段。得出的结论是，在存在串联电阻的多细胞标本中，记录到的方形电压脉冲并不表明跨膜电位受到了电压控制。并联通路的存在会产生不准确的电流密度值。串联电阻和并联电阻都不会在电流记录中产生“缺口”。
