600 ns pulse electric field-induced phosphatidylinositol4,5-bisphosphate depletion

Abstract

The interaction between nsPEF-induced Ca2+ release and nsPEF-induced phosphatidylinositol4,5-bisphosphate (PIP2) hydrolysis is not well understood. To better understand this interrelation we monitored intracellular calcium changes, in cells loaded with Calcium Green-1 AM, and generation of PIP2 hydrolysis byproducts (inositol-1,4,5-trisphosphate (IP3) and diacylglycerol (DAG)) in cells transfected with one of two fluorescent reporter genes: PLCδ-PH-EGFP or GFP-C1-PKCγ-C1a. The percentage fluorescence differences (ΔF %) after exposures were determined. Upon nsPEF impact, we found that in the absence of extracellular Ca2+ the population of IP3 liberated during nsPEF exposure (ΔF 6%±3, n=22), is diminished compared to the response in the presence of calcium (ΔF 84%±15, n=20). The production of DAG in the absence of extracellular Ca2+ (ΔF 29%±5, n=25), as well as in cells exposed to thapsigargin (ΔF 40%±12, n=15), was not statistically different from cells exposed in the presence of extracellular calcium (ΔF 22±6%, n=18). This finding suggests that the change in intracellular calcium concentration is not solely driving the observed response. Interestingly, the DAG produced in the absence of Ca2+ is the strongest near the membrane regions facing the electrodes, whereas the presence of extracellular Ca2+ leads to a whole cell response. The reported observations of Ca2+ dynamics combined with IP3 and DAG production suggest that nsPEF may cause a direct effect on the phospholipids within the plasma membrane.