Submicrosecond intense pulsed electric field effects on intracellular free calcium: mechanisms and effects

Application of submicrosecond intense pulsed electric fields (sm/i-PEF) to cells results in rapid, transient rises in intracellular free calcium concentrations ([Ca⁺⁺]_i) in human blood neutrophils, human promyelocytic leukemia cells (HL60), and human T-cell leukemia cells (Jurkat cells). The magnitude of the rise in [Ca⁺⁺]_i in human neutrophils is related to the intensity of applied sm/i-PEF. Some 10-50% of the rise in [Ca⁺⁺]_i triggered by 300-ns pulses is due to release of Ca⁺⁺ from intracellular sources, while maximally 10% of the rise in [Ca⁺⁺]_i triggered by 60-ns pulses is due to release from intracellular sources. Repetition of a sm/i-PEF application of lesser intensity than the first pulse fails to induce a rise in [Ca⁺⁺]_i, while a second pulse of equal or greater intensity elicits a small or moderate rise, respectively. When sm/i-PEF applications were examined for effects on cellular function, no effect was observed on neutrophil phagocytosis. Suppression of spontaneous H₂O₂ production was observed after a 300-ns, 60-kV/cm pulse, and transient suppression of neutrophil chemotaxis was observed following a 300-ns and 60-ns, 60-kV/cm pulse. No evidence of proton influx/efflux was found following sm/i-PEF application. sm/i-PEF applications may allow manipulation of selected cell behaviors/function based on their ability to initiate changes in [Ca⁺⁺]_i.