ROLE OF INTRACELLULAR CALCIUM-CONCENTRATION ON TUMOR-CELL DEATH FROM HYPERTHERMIA

The intracellular calcium ion concentration of SCK cells was measured after the cells were heated to determine the relationship between ther motolerance and intracellular calcium concentration. SCK cells, which are breast cancer cells that spontaneously arise in A/J mice, were use d. Exponentially growing cells were trypsinized and incubated for 60 m in with fura-2/AM at a concentration of 10 mu M The incubation was car ried out at a density of 1x10(6) cells/ml in serum-free RPMI medium. T hermotolerance was induced by incubating cells for 5 h at 37 degrees C after heating them at 43 degrees C for 30 min. When heated at 44 degr ees C in a calcium containing buffer, the intracellular calcium concen tration of non-thermotolerant and thermotolerant cells increased conti nuously as the cells were heated for longer periods of time. The same increase in intracellular calcium concentration was seen in these two cell lines when heated at 43 degrees C in a calcium-free buffer. Thus, our data indicated that intracellular calcium ion increased during he ating due to an influx into the cytoplasm from both internal stores an d the extracellular medium.