Effects of energy controllable steep pulses on intracellular calcium concentration and cell membrane potential

Our previous experiments showed that steep pulses could kill tumor cells, but the mechanism is unclear yet. This study was to probe the effects of different dosages of energy controllable steep pulses on intracellular concentration of dissociative calcium ion ([Ca2+]i) and cell membrane potential.

The mammary carcinoma cells MDA-MB-231 were divided into control group and 5 different dosages of Energy Controllable Steep Pulses (ECSP) treatment groups. The calcium ion in each group was labeled by Fluo-3/AM individually and the cell membrane potential was labeled by DiBAC4 (3). The mean fluorescence intensity of fluorescent probe in mammary carcinoma cells was observed in quiet state by laser confocal microscopy after ECSP treatment The changes of calcium concentration and cell membrane potential in cells after ECSP treatment were analyzed. The changes of intracellular [Ca2+]i after ECSP treatment were also observed with and without calcium ion outside of the cells.

The calcium ion outside of cells influx with lower dosage of pulse in quiet state. With the dosage increase, the intracellular calcium ion outflow. In real time kinetic detection, the mean fluorescence intensity of intracellular calcium ion was increased with the pulse electric field intensity raised in the lower ECSP. When the voltage was 285V, frequency was 100Hz, the [Ca2+]i decreased. The increase of intracellular calcium ion concentration was decreased without calcium ion than with calcium ion outside of cells, but still raised gradually. The lower dosage of ECSP could induce the fluorescence intensity of DiBAC4 (3) in cells increase, which showed that the lower dosage of ECSP could induce the depolarization of cells. With the dosage raised, the fluorescence intensity of DiBAC4 (3) in cells attenuated. This dosage of ECSP could induce the superpolarization of cell membrane.

The lower dosage of ECSP can induce the depolarization of cell membrane and induce the inter flow of calcium ion outside of cell membrane. The higher dosage of ECSP can directly destroy the cell membrane and induce the superpolarization of cell membrane, then induce the outflow of intracellular calcium ion which causes the necrosis of tumor cells.