Cellular ion content changes during and after hyperthermia.

The potassium (K) level in mouse mastocytoma P815 cells undergoes a 40% reduction within 30 minutes of incubation at 43°C. It decreases further when the cells return to 37°C after a 60 minute 43°C incubation. A smaller change (20%) occurs after a 60 minute incubation at 41°C. Furthermore, nearly all of the lost K recovers in two hours after a subsequent incubation at 37°C. On the other hand, the sodium level in the cells increases by an amount much smaller than the potassium changes. However, the net loss of cations from the cells undergoing hyperthermia does not induce a simultaneous reduction of intracellular water volume.