Microelectrode measurements of the transmembrane potential in baby hamster kidney, (Chinese hamster ovary), NG108–15 Neuroblastoma and Swiss 3T3 Cells at 37.0 or 43–0°C

Abstract

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 demonsrated 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°, 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°C, regardless of the time of exposure at 43.0° (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.

Key Words:

• trans membrane potential
• microelectrodes
• cell contact