Heat-induced K+ loss, trypan blue uptake, and cell lysis in different cell lines: effect of serum

Experiments were performed with three different cell lines, mouse fibroblast LM cells, HeLa S3 cells, and Ehrlich Ascites Tumor (EAT) cells, to establish the possible importance of hyperthermic-induced alterations in cellular K+ content in the mechanism of cell killing by heat. At different time points after the hyperthermic treatment, the K+ content in the cells, the uptake of the dye Trypan Blue (TB), and cell lysis were assayed. Heat-induced K+ loss preceded TB uptake which was followed by the heat-induced cell lysis. Lysis was assayed as disappearance of cells by counting the cells at different time points in a hematocytometer. The presence of serum during and after the heat treatment was of considerable importance with respect to K+ loss and TB uptake. K+ loss and TB uptake after the heat treatment were less when serum was present during and after hyperthermia. To protect against cell lysis, however, the serum had to be present during a preincubation period of 24 h. Clonogenic ability was not affected by the presence of serum. It is concluded that the intracellular K+ level of hyperthermic-treated cells is not a direct cause for cell killing and that heat-induced alterations in the cell leading to cell lysis are different from the processes decreasing cellular K+ content and permeabilizing the plasma membrane for trypan blue.