HEAT-INDUCED CHANGES IN INTRACELLULAR SODIUM AND MEMBRANE-POTENTIAL -LACK OF A ROLE IN CELL-KILLING AND THERMOTOLERANCE

Hyperthermia induces transient changes in intracellular free sodium le vels and membrane potential, The possible role of these changes in cel l killing by hyperthermia and thermotolerance has been evaluated using Chinese hamster ovary IS1 and HeLa cells. Intracellular sodium was me asured with Sodium Green and SBFI, while membrane potential was measur ed with the oxonol dye diBAC(4)(3). Heating at either 42.0 or 45.0 deg rees C caused nearly the same decrease in free [Na+](i) from about 20 mM in unheated cells to 5-7 mM in heated cells, However, survival diff ered by over two orders of magnitude after heating for 30 min at these two temperatures, In addition, blockage of the heat-induced decrease in [Na+](i) using ouabain and/or amiloride did not affect the survival curves for heated cells. Hyperthermia also induced a membrane hyperpo larization of 15 mV after 15 min at 42.0 degrees C or 35 mV after 15 m in at 45.0 degrees C which could be blocked with ouabain and amiloride , Both the free [Na+](i) and membrane potential recovered to near base line levels within 30-40 min after heating. Induction of thermotoleran ce using a 45.0 degrees C, 10-min heat treatment also was not affected by ouabain and/or amiloride, Finally, thermotolerant cells experience d the same heat-induced changes in free [Na+](i) and membrane potentia l as non-thermotolerant cells. We conclude that the heat-induced chang es in free [Na+](i) and membrane potential are not directly related to cell killing by hyperthermia or thermotolerance. (C) 1996 by Radiatio n Research Society