Electrical fields enhance growth of cancer spheroids by reactive oxygen species and intracellular Ca2+.
A single electrical field pulse (500 V/m) with a duration of 60 s increased tumor outgrowth over a postpulse period of 24 h. RNA staining with acridine orange showed a rise in RNA content in pulsed spheroids, indicating stimulation of cell cycle activity. The electropulse induced an intracellular Ca2+ concentration ([Ca2+]i) transient that started approximately 40 s after the onset of the electrical field. Neither the presence of extracellular Ni2+ (0.5 mM) nor the absence of extracellular Ca2+ impeded the [Ca2+]i rise. It was, however, totally blocked by thapsigargin (1 microM), indicating that the initial Ca2+ response is due to Ca2+ release from intracellular stores. The [Ca2+]i transient was paralleled by an increase in reactive oxygen species (ROS), as revealed using 2',7'-dichlorofluorescein diacetate as an indicator. The radical scavengers N-acetyl-L-cysteine (NAC)(20 mM) and dehydroascorbate (5 mM) inhibited both ROS production and the [Ca2+]i transient during electrical field treatment. The mitogenic activation was dependent on the rise in [Ca2+]i because inhibition of Ca2+ release during electrical field treatment by addition of either thapsigargin or NAC to the incubation medium abolished the observed effect. We conclude that a single, direct current electrical field pulse induces production of ROS, which in turn mediate Ca2+ release from intracellular stores and activate cell cycle activity in multicellular spheroids.
Wartenberg
M
M
Institute for Neurophysiology, University of Cologne, Germany.
Hescheler
J
J
Sauer
H
H
D002118:Calcium / Q000502:physiology*; D002451:Cell Compartmentation; D002455:Cell Division; D004574:Electromagnetic Fields; D006801:Humans; D008938:Mitosis; D009940:Organoids; D017382:Reactive Oxygen Species / Q000502:physiology*; D014407:Tumor Cells, Cultured / Q000166:cytology*
D017382:Reactive Oxygen Species; D002118:Calcium