Hyperthermia-induced intracellular ionic level changes in tumor cells.

The intracellular content of potassium (K) ions in P815 cells decreases when the media pH is lowered, and it increases when media pH is raised. The determination of the ion content therefore requires accurate control of the medium pH. The K ion content measured both by the flame emission method and by the K analog. 86Rb, exhibits a decline when the cells are incubated at 43 degrees C at a fixed pH chosen between 7.4 and 6.7. The chloride content also decreases while the sodium content does not change by a significant amount. Under the same hyperthermic conditions the intracellular pH decreases by a fraction of a pH unit. Simultaneously, the cell water volume increases by 20%, as measured by tritiated water. In the final analysis, hyperthermia produces an apparent deficit in the cellular osmolarity. A possible explanation is given.