Variations of Intracellular Ca2+ Mobilization Initiated by Nanosecond and Microsecond Electrical Pulses in HeLa Cells

Goal: Herein, the variations in transient Ca
²⁺
mobilizations in HeLa cells exposed to a single, non-thermal pulsed electric field (PEF) are described. Methods: Three PEF waveforms categorized by pulse duration and intensity were used to deduce the kinetics involved in Ca
²⁺
mobilization. A fast microscopic fluorescent imaging system and a fluorescent molecular probe were used to observe transient intracellular Ca
²⁺
mobilization after pulse exposure. The sources and pathways in the transient Ca
²⁺
mobilizations were investigated using an inhibitor of inositol-1,4,5-trisphosphate receptor (IP3R) on the endoplasmic reticulum (ER) along with a Ca
²⁺
-free buffer. Results: When exposed to the 10-μs-long PEF, the Ca
²⁺
concentration increased mainly at the cathodic region near the membrane. However, Ca
²⁺
concentration increased at both anodic and cathodic regions when Na
⁺
concentration in the buffer was reduced. Ca
²⁺
concentration increased only in the presence of extracellular Ca
²⁺
. Conclusion: These results suggest that the 10-μs PEF takes a large amount of extracellular Na
⁺
into the cell through the electropermeabilized plasma membrane, especially at the anodic side, resulting in the suppression of the Ca
²⁺
influx. On the contrary, the 20-ns-long PEF increased Ca
²⁺
concentration in the surrounding region of the nucleus only in the presence of extracellular Ca
²⁺
. The PEF exposure with inhibition of the IP3R indicates that increased Ca
²⁺
ions are released from the ER via the activated IP3R. Significance: These mechanisms could induce specific cell responses, such as Ca
²⁺
oscillations, Ca
²⁺
waves, and Ca
²⁺
puffs.