Ion‐sensitive microelectrode measurements of free intracellular chloride and potassium concentrations in hyperthermia‐treated neuroblastoma cells

Murine NG108‐15 neuroblastoma cells were heated for times of 5–40 min at 45.5°C, and survival ranged from 0.7–0.0015, respectively. Ion‐sensitive micro‐electrodes (ISM) were used to measure the free intracellular concentrations of Cl⁻ and K⁺ immediately after heating and up to 30 hr later. The free intracellular Cl⁻ and K⁺ concentrations, [Cl⁻]_i and [K⁺]_i respectively, of the heated cells remained identical to those of the controls for the first 10 hr after heating. At later times, some cells had increased [Cl⁻]_i values and decreased [K⁺]_i values identical to those of the extracellular medium. These cells had a mottled morphology, no longer excluded the vital stain trypan blue, and had no membrane potential. The number of these dye‐including, physiologically dead cells increased with time, and was always greater following longer heating times. No changes in mean cellular volume were observed until 25 hr after heating. All trypan‐blue‐excluding, physiologically live cells had the same [Cl⁻]_i and [K⁺]_i as the control cells, even when the majority of them were destined for clonogenic death. Copyright © 1986 Wiley‐Liss, Inc.