Correlation between cell killing effect and cell membrane potential after heat treatment: analysis using fluorescent dye and flow cytometry.

Exposure of mammalian cells to a temperature between 42 and 44 degrees C produces multiple effects on cellular metabolism. However, none of these effects have been demonstrated to be casually related to cell death. The plasma membrane has also been suggested to be one of the targets for hyperthermia. Hyperthermia influences the membrane fluidity and membrane fluidity affects both passive diffusion and active transport process. Here, we examined the effect of hyperthermia on the transmembrane potential V-79 cells using a lopophilic probe and flow cytometry. The underlying principle on which this method is based is that a freely diffusible cation distributes itself across the membrane according with the transmembrane potential and with the concentration gradient. By these methods, we tried to find the relation between the change of surviving fraction and membrane potential. We revealed that the membrane potential becomes to be depolarized by heat treatment between 41 and 44 degrees C immediately after heat treatment. In the relationship between the change in membrane potential and cell surviving fraction, the difference between 43 and 44 degrees C was not statistically significant but between 42 and 43 degrees C was statistically significant. These results imply that the cell membrane (potassium ion channel) is one of the targets of heat treatment and that duration of depolarized condition leads to cell death.