After assaying fluorescence in Ca2+-free medium, cells were treated with any one of the drugs such as caffeine, ATP and thapsigargin to induce a transient change in intracellular calcium concentration.
Exposure of PC-12 cells to a time-varying 1.51 T magnetic field inhibited an increase in the intracellular Ca2+ concentration induced by addition of caffeine to Ca2+-free medium. This inhibition occurred after a 15 min exposure and was maintained for at least two hours.
The intracellular Ca2+ concentration increased in cells loaded with cyclic ADP-ribose (a ryanodine receptor stimulator), and two hours exposure significantly suppressed the increase. Addition of ATP induced a transient increase in intracellular Ca2+ release mediated by inositol trisphosphate receptor. This increase was strongly inhibited by the exposure.
The data indicated that the magnetic field exposure strongly inhibited Ca2+ release mediated by both inositol trisphosphate and ryanodine receptors. However, thapsigargin-induced Ca2+ influx across the cell membrane was unaffected.
The ATP concentration was maintained at the normal level during the 2 h exposure, indicating that ATP hydrolysis was unchanged.