Electric field-induced changes in agonist-stimulated calcium fluxes of human HL-60 leukemia cells

The mechanism of biological effects of extremely-low-frequency electric and magnetic fields may involve induced changes of Ca²⁺ transport through plasma membrane ion channels. In this study we investigated the effects of externally applied, low-intensity 60 Hz electric (E) fields (0.5 V/m, current density 0.8 A/m²⁺) on the agonist-induced Ca²⁺ fluxes of HL-60 leukemia cells. The suspensions of HL-60 cells received E-field or sham exposure for 60 min and were simultaneously stimulated either by 1 μM ATP or by 100 μM histamine or were not stimulated at all. After E-field or sham exposure, the responses of the intracellular calcium levels of the cells to different concentrations of ATP (0.2–100 μM) were assessed. Compared with control cells, exposure of ATP-activated cells to an E-field resulted in a 20–30% decrease in the magnitude of Ca²⁺]_i elevation induced by a low concentration of ATP (<1 μM). In contrast, exposure of histamine-activated HL-60 cells resulted in a 20–40% increase of ATP-induced elevation of Ca²⁺]_i. E-field exposure had no effect on non-activated cells. Kinetic analysis of concentration-response plots also showed that compared with control cells, exposure to the E-field resulted in increases of the Michaelis constant, K_m, value in ATP-treated cells and of the maximal Ca²⁺]_i peak rise in histamine-treated HL-60 cells. The observed effects were reversible, indicating the absence of permanent structural damages induced by acute 60 min exposure to electric fields. These results demonstrate that low-intensity electric fields can alter calcium distribution in cells, most probably due to the effect on receptor-operated Ca²⁺ and/or ion channels. Bioelectromagnetics 19:366–376, 1998. © 1998 Wiley-Liss, Inc.