Department of Electrical and Biomedical Engineering, College of Engineering, University of Nevada, Reno.
Department of Pharmacology, University of Nevada, Reno School of Medicine, Reno, Nevada.
Biophys J. 2021 Feb 2;120(3):556-567. doi: 10.1016/j.bpj.2020.12.017. Epub 2020 Dec 25.
Cellular effects of nanosecond-pulsed electric field exposures can be attenuated by an electric field reversal, a phenomenon called bipolar pulse cancellation. Our investigations of this phenomenon in neuroendocrine adrenal chromaffin cells show that a single 2-ns, 16 MV/m unipolar pulse elicited a rapid, transient rise in intracellular Ca levels due to Ca influx through voltage-gated calcium channels. The response was eliminated by a 2-ns bipolar pulse with positive and negative phases of equal duration and amplitude and fully restored (unipolar-equivalent response) when the delay between each phase of the bipolar pulse was 30 ns. Longer interphase intervals evoked Ca responses that were greater in magnitude than those evoked by a unipolar pulse (stimulation). Cancellation was also observed when the amplitude of the second (negative) phase of the bipolar pulse was half that of the first (positive) phase but progressively lost as the amplitude of the second phase was incrementally increased above that of the first phase. When the amplitude of the second phase was twice that of the first phase, there was stimulation. By comparing the experimental results for each manipulation of the bipolar pulse waveform with analytical calculations of capacitive membrane charging/discharging, also known as accelerated membrane discharge mechanism, we show that the transition from cancellation to unipolar-equivalent stimulation broadly agrees with this model. Taken as a whole, our results demonstrate that electrostimulation of adrenal chromaffin cells with ultrashort pulses can be modulated with interphase intervals of tens of nanoseconds, a prediction of the accelerated membrane discharge mechanism not previously observed in other bipolar pulse cancellation studies. Such modulation of Ca responses in a neural-type cell is promising for the potential use of nanosecond bipolar pulse technologies for remote electrostimulation applications for neuromodulation.
纳秒级脉冲电场的细胞效应可以通过电场反转来减弱，这种现象称为双极脉冲消除。我们在神经内分泌肾上腺嗜铬细胞中对这一现象的研究表明，单个 2ns、16MV/m 的单极脉冲会通过电压门控钙通道引起细胞内 Ca 水平的快速、短暂上升。这种反应被具有相同持续时间和幅度的正负相 2ns 双极脉冲消除，当双极脉冲每相之间的延迟为 30ns 时，完全恢复（单极等效反应）。较长的相间间隔会引起比单极脉冲（刺激）更大幅度的 Ca 反应。当双极脉冲第二（负）相的幅度是第一（正）相的一半时，也观察到了消除现象，但随着第二相的幅度逐渐增加超过第一相，消除逐渐消失。当第二相的幅度是第一相的两倍时，就会出现刺激。通过将双极脉冲波形的每种操作的实验结果与电容膜充电/放电的分析计算（也称为加速膜放电机制）进行比较，我们表明，从消除到单极等效刺激的转变与该模型大体一致。总的来说，我们的结果表明，用超短脉冲对肾上腺嗜铬细胞进行电刺激可以通过数十纳秒的相间间隔来调节，这是加速膜放电机制的预测，在以前的其他双极脉冲消除研究中没有观察到。这种对神经样细胞中 Ca 反应的调制有望为纳米双极脉冲技术在远程电刺激神经调节中的潜在应用提供可能。
