Resolving the spatial kinetics of electric pulse-induced ion release

Exposure of cells to nanosecond pulsed electric fields (nsPEF) causes a rapid increase in intracellular calcium. The mechanism(s) responsible for this calcium burst remains unknown, but is hypothesized to be from direct influx through nanopores, the activation of specific ion channels, or direct disruption of organelles. It is likely, however, that several mechanisms are involved/activated, thereby resulting in a complex chain of events that are difficult to separate by slow imaging methods. In this letter, we describe a novel high-speed imaging system capable of determining the spatial location of calcium bursts within a single cell following nsPEF exposure. Preliminary data in rodent neuroblastoma cells are presented, demonstrating the ability of this system to track the location of calcium bursts in vitro within milliseconds of exposure. These data reveal that calcium ions enter the cell from the plasma membrane regions closest to the electrodes (poles), and that intracellular calcium release occurs in the absence of extracellular calcium. We believe that this novel technique will allow us to temporally and spatially separate various nsPEF-induced effects, leading to powerful insights into the mechanism(s) of interaction between electric fields and cellular membranes.