Relation of transmembrane potential to cell survival following hyperthermia in HeLa cells

Hyperthermia induces cell death and the usual endpoint to study this is the ability of the cells to form colonies. Hyperthermia is also known to alter membrane characteristics, especially transmembrane potential and this has been correlated with duration and degree of heating. The aim of the present study was to see the correlation between changes in membrane potential and clonogenic ability of HeLa cells after heat treatment of 41-44 degrees C. Membrane potential was measured by the fluorescence polarization of the plasma membrane probe 3,3'-dipentyloxacarbocyanine by flow cytometry. Cell survival was assessed by colony formation assay. The fluorescence intensity increased and cell survival decreased with an increase in temperature. The fall in survival following heat treatment closely paralleled the increase in fluorescent intensity, especially heat treatments of 60 min or more. After 2 h of heating at 44 degrees C, the surviving fraction decreased to 1% and the fluorescence intensity increased to 154.84% of the unheated controls. This study suggests that measurement of membrane potential by flow cytometry may potentially be an alternative to colony forming assay for assessing cell survival. Since the results of membrane potential measurements are available immediately, this has implications for its potential use as a predictive assay of thermosensitivity.