Extracellular calcium differentially affects intracellular responses to nanosecond pulsed electric fields

Abstract

Nanosecond pulsed electric fields (nsPEFs) have received considerable attention because of their unique effects on living cells. Exposure of cultured cells to nsPEFs is known to induce Ca²⁺ influx by forming small pores in the plasma membrane. Furthermore, nsPEFs have been reported to induce activation of multiple cellular signaling pathways. To examine the relationship between Ca²⁺ influx and intracellular signaling events after nsPEF exposure, we applied nsPEFs to HeLa S3 cells suspended in either Ca²⁺-free or Ca²⁺-containing medium and analyzed the activation of signaling pathways. We observed that the presence of extracellular Ca²⁺ was required for AMPK activation but dispensable for the initiation of stress responses in nsPEF-exposed HeLa S3 cells. JNK and p38, which are major regulatory factors in MAPK pathways, were activated by nsPEFs irrespective of the presence or absence of extracellular Ca²⁺. The absence of extracellular Ca²⁺, however, led to augmented phosphorylation of JNK and p38, suggesting positive effects of Ca²⁺ influx on negative feedback controls in MAPK pathways. Taken together, these observations demonstrate that Ca²⁺ influx induced by nsPEFs differentially participates in intracellular signaling events.

Keywords: Nanosecond pulsed electric field, calcium, signal transduction.