Na+/K+ ATPase activity in mouse lung fibroblasts and HeLa S3 cells during and after hyperthermia

The ouabain-sensitive ATP-hydrolysing activity, representing the Na+/K+ ATPase capacity, of isolated membranes and whole cells during and after hyperthermia treatments was investigated. In isolated membranes no heat damage after treatments up to 46 degrees C during 45 min or up to 6 h at 44 degrees C could be detected. The ATP hydrolysing activity of Na+/K+ ATPase seems not to be impaired by direct heat attack in the range of commonly used hyperthermic temperatures (39-46 degrees C). Heat effects on the ATP hydrolysing activity of Na+/K+ ATPase of whole mouse fibroblasts could only be detected after heat doses (greater than 40 min at 44 degrees C) necessary to yield over 99 per cent dead cells. Potassium influx, measured with 86RB+ as the K+ tracer, was initially enhanced during incubation at 44 degrees C proportionally with the enhancement of the ATP-hydrolysing activity after raising the temperature. Replacement of non-lethally (10 min at 44 degrees C) and lethally (40 min at 44 degrees C) treated mouse fibroblasts to 37 degrees C showed complete reversibility of the enhanced activity at 44 degrees C to the control level at 37 degrees C. For comparison, the ATP-hydrolysing activity of Na+/K+ ATPase of HeLa S3 cells growing as monolayer was also tested. The activity after heat treatments up to 60 min at 44 degrees C was also found to be unchanged in these experiments. No indication of irreversible damage to the ATP-hydrolysing capacity of mouse fibroblasts and HeLa S3 cells, or K+ pumping activity of mouse fibroblasts by heat treatments up to 40 min at 44 degrees C was found.