THE ROLE OF INTRACELLULAR FREE CALCIUM IN THE CELLULAR-RESPONSE TO HYPERTHERMIA

The intracellular free calcium (Ca-i(++)) concentration was measured i n several cell lines after heating at 45.0 degrees C using flow cytome try with indo-1. Chinese hamster ovary 10B2 (CHO) cells do not stain w ell with indo-1, so a CHO mutant cell line (CHO IS1) isolated in our l aboratory with much-improved stainability for indo-1 was used to study CA(i)(++) changes in heated CHO cells. BALB-3T3 (mouse) and EJ30 (hum an) cells were also studied. Cells were heated in the sample holder of the cell sorter in order to measure Ca-i(++) within seconds after hea ting. Ca-i(++) increased rapidly within the first 5 min of heating at 45.0 degrees C in all three lines, though the magnitude of the increas e varied for each cell line. The Ca-i(++) returned rapidly to baseline after heating in CHO ISI cells and BALB-3T3 cells. After 5 min of hea ting, the Ca-i(++) plateaued in the EJ30 and IS 1 cells, but decreased in the 3T3 cells. There was an inverse relationship between the Ca-i( ++) after 10 min at 45 degrees C and survival for the different cell l ines. Thermotolerant cells experienced a similar change in Ca-i(++) du ring heating as non-thermotolerant cells, though the kinetics were som ewhat different for the IS1 cells. A bimodal distribution of Ca-i(++) developed in EJ30 cells by 2 min after heating. Cells sorted from the near-normal Ca-i(++) region of the histogram had a 2-fold higher survi val rate than the cells which had a high Ca-i(++) concentration. These data support the view that Ca-i(++) changes during heating are not th e principal factor in heat-induced cell death.