MICROELECTRODE MEASUREMENTS OF THE TRANSMEMBRANE POTENTIAL IN BABY HAMSTER-KIDNEY, (CHINESE-HAMSTER OVARY), NG108-15 NEUROBLASTOMA AND SWISS 3T3-CELLS AT 37.0-DEGREES-C OR 43.0-DEGREES-C

Hyperthermia affects the physical state and function of the plasma membrane. This could alter the transmembrane potential (V(m)) and associated functions in a manner that promotes cell killing. Previous investigations have reported differing results of the effect of heat on V(m), possibly due to artifacts associated with the methods employed to measure V(m) indirectly. One such artifact is a membrane depolarization induced by cationic probes, as demonstrated in this paper. In this study, glass microelectrodes were used to avoid these artifacts and to make direct electrical measurements of V(m). Following 25 min-30 min at 43.0-degrees-C, The mean V(m) of Chinese hamster ovary (CHO) cells, within clusters of six or more cells, decreased from -16 +/- 5 to -38 +/- 6 mV, and remained at these levels during incubation times up to 3 h. All CHO cells resumed a normal V(m) within 4.5 h after returning to 37.0-degrees-C, regardless of the time of exposure at 43.0-degrees-C (0.5 to 3.0 h, with survival levels of 0.7 and 0.001, respectively). The membrane hyperpolarization decreased with cell to cell contact to where isolated cells exhibited no hyperpolarization. CHO cultures with different cell densities (number of cells per cm2), and thus differing degrees of cell to cell contact, were heated and then subjected to the colony formation assay. The degree of cell to cell contact at the time of heating had no effect on survival. Hence, the heat-induced, cell contact dependent hypolarization of CHO cell membranes was unrelated to clonogenic survival. Hyperthermia did not alter the transmembrane potential of either baby hamster kidney(BHK), NG108-15 or Swiss 3T3 cells, demonstrating further that a change in V(m) is not involved in hyperthermic cell death, and that the response of V(m) to hyperthermia is cell line dependent.