Modification of the ionic environment in the tumor cell by hyperthermia.

Tumor cells submitted to hyperthermia (45 degrees C) showed changes in the ionic composition: Increased calcium and decreased potassium concentrations. These changes are likely to affect vital functions of the cell. The observed decrease in ATP concentration supports the hypothesis that hyperthermia affects the ATP-dependent extrusion mechanism of the cell and, consequently, induces that ionic environment modification. Lactate production was also decreased by hyperthermia, a phenomenon that could be related to the fall in potassium concentration. The intracellular increase in Ca2-concentration during hyperthermia appears to support the earlier hypothesis on the role of Ca2+ in tumor inhibition by hyperthermia.