Saints-Pères Paris Institute for the Neurosciences, Centre National de la Recherche Scientifique, Université de Paris, 75006 Paris, France
eNeuro. 2021 Feb 1;8(1). doi: 10.1523/ENEURO.0461-20.2020. Print 2021 Jan-Feb.
Intracellular recordings using sharp microelectrodes often rely on a technique called discontinuous current-clamp (DCC) to accurately record the membrane potential while injecting current through the same microelectrode. It is well known that a poor choice of DCC switching rate can lead to underestimation or overestimation of the cell potential; however, its effect on the cell firing is rarely discussed. Here, we show that suboptimal switching rates lead to an overestimation of cell excitability. We performed intracellular recordings of mouse spinal motoneurons and recorded their firing in response to pulses and ramps of current in Bridge and DCC mode at various switching rates. We demonstrate that using an incorrect (too low) DCC frequency leads not only to an underestimation of the input resistance, but also, paradoxically, to an artificial overestimation of the firing of these cells: neurons fire at lower current, and at higher frequencies than at higher DCC rates, or than the same neuron recorded in Bridge mode. These effects are dependent on the membrane time constant of the recorded cell, and special care needs to be taken in large cells with very short time constants. Our work highlights the importance of choosing an appropriate DCC switching rate to obtain not only accurate membrane potential readings but also an accurate representation of the firing of the cell.
使用锋利微电极进行细胞内记录通常依赖于一种称为不连续电流钳（DCC）的技术，该技术可在通过同一微电极注入电流的同时准确记录膜电位。众所周知，DCC 切换率选择不当会导致细胞电位的低估或高估；然而，其对细胞放电的影响很少被讨论。在这里，我们表明次优的切换率会导致细胞兴奋性的高估。我们对小鼠脊髓运动神经元进行了细胞内记录，并在各种切换率下以桥接和 DCC 模式记录了它们对电流脉冲和斜坡的放电。我们证明，使用不正确（太低）的 DCC 频率不仅会导致输入电阻的低估，而且还会矛盾地导致这些细胞放电的人为高估：神经元在较低的电流下放电，并且在比 DCC 频率更高或与在桥接模式下记录的相同神经元更高的频率下放电。这些效应取决于记录细胞的膜时间常数，对于具有非常短时间常数的大细胞，需要特别小心。我们的工作强调了选择适当的 DCC 切换率的重要性，以不仅获得准确的膜电位读数，而且还获得细胞放电的准确表示。
