Exposure System Dependent Calcium Influx in Chromaffin Cells by Nanosecond Electric Pulse- Field Reflections at Dielectric Interface

Nanosecond electric pulses have been successfully used as a novel electrical stimulus for evoking a dependent catecholamine release from the bovine adrenal chromaffin cells. It was observed that the duration of calcium influx varies depending on the exposure system. For example, cells exposed to 5 ns and 5MV/m pulses by a gold strip exposure chamber elicited calcium responses similar to the physiological stimulus, nicotinic cholinergic receptor activation. On the other hand, recent exposure systems utilizing tungsten rod electrodes evoke an undesired calcium response that is relatively long-lived even by exposure of the same pulse. Hence, the objective of the project is to perform numerical modeling to identify the local E-field in the rod electrode system that may cause a profound effect and to improve the electrode design to consistently and reliably elicit a calcium influx trace similar to that by the physiological stimulus. In this study, we pay attention to localized reflections of E-field in the exposure chambers. The E-field inside the gold strip chamber propagates parallel to the glass dish, whereas that of rod electrodes propagates in the vertical direction. In the latter case, a significant E-field reflection occurred at the surface of a glass dish, causing exposure of high E-field. Consecutive cell modeling proved that the transmembrane potential (TMP) was increased as high as twice, depending on the angle of propagation. The gold strip chamber, on the other hand, did not show a significant E-field reflection as the E-field propagates parallel to the dish. Electrodes that cause small or no E-field reflection are under development and will prove if eliminating the E-field reflections can trigger the calcium trace that is similar to the physiological stimulus or the gold strip chamber.