Effect of hyperthermia on transmembrane potential of HeLa cells--a flow cytometric analysis

The effect of hyperthermia on transmembrane potential was studied in HeLa cells in vitro using a 3',3'-dipentyl oxacarbocyanine [Di-0-C5(3)], a lipophilic cation probe that equilibrates across the plasma membrane according to the transmembrane potential. Uptake of the fluorescent probe was measured by flow cytometry. The flourescent intensity (FI) increased with increase in temperature, and the increase was statistically significant when the duration of heat treatment was 30 minutes or more. At each temperature studied the depolarization was higher after longer duration of heat treatment (p value: 41 degrees C < 0.05; 42 degrees C < 0.005; 43 degrees C < 0.001 and 44 degrees C < 0.001, respectively). The lack of significant depolarization after shorter duration of heating, particularly at lower temperatures could be due to the repair of membrane damage that could have occurred in the holding interval between heating and measurement. The results suggest that depolarization of membrane potential, i.e. increase in the intracellular cation concentration, can be considered as an indicator of cell injury by hyperthermia and may be mechanistically related to cell death by heat treatment. The technique may be suitable for studying repair of damage after hyperthermia.