ALTERATIONS OF INTRACELLULAR CALCIUM-CONCENTRATION IN MICE NEUROBLASTOMA-CELLS BY ELECTRICAL-FIELD AND UVA

By using a FURA2 ratio imaging method, the intracellular free calcium concentration was investigated in cultured mice neuroblastoma cells un der the influence of an amplitude-modulated (AM) held (5 kHz sine wave AM 16 Hz sinusoidal 800 V/m and 80 V/m), as well as of electric held pulses (300-ms unipolar pulses of 1000 V/m and 800 V/m, 5 pulses durin g 10 s and 50 pulses during 100 s). An increase in free intracellular calcium was found in about 50% of cells after field application, where as in control experiments only about 20% of the cells showed similar i ncreases. However, this effect depended on the amount of UV irradiatio n used for excitation of FURA2 fluorescence. Experiments with 1/30 to former total illumination no longer demonstrated an increase in contro l cells or in cells treated with AM fields. The number of cells showin g calcium increase after the application of pulsed fields was reduced significantly. Therefore, the UV light itself, applied as double flash es for the fluorescence measurement, activates the cellular calcium re gulation. These findings offer a possible explanation for the low repr oducibility of held effects found in different laboratories, in which investigations were performed with different equipment using different intensities of UV excitation. (C) 1997 Wiley-Liss, Inc.