Blue light inhibits mitosis in tissue culture cells

Irradiation of the mitotic (prophase and prometaphase) tissue culture PK (p ig kidney embryo) cells using mercury are lamp and band-pass filters postpo ned or inhibited anaphase onset. The biological responses observed after ir radiation were: (i) normal cell division, (ii) delay in metaphase and then normal anaphase and incomplete cytokinesis, (iii) exit into interphase with out separation of chromosomes, (iv) complete mitotic blockage. Cell sensiti vity to the light at wavelengths from 423 and 488 nm was nearly the same; t o the near UV light (wavelength 360 nm) it was 5-10 times more; to the gree n light (wavelength > 500 nm) it was at least 10 times less. To elucidate t he possible mechanism of the action of blue light we measured cell adsorpti on and examined cell autofluorescence. Autofluorescence of cytoplasmic gran ules was exited at wavelengths of 450-490 nm, but not at > 500 nm. In mitot ic cells fluorescent granules accumulated around the spindle. We suppose bl ue light irradiation induces formation of the free radicals and/or peroxide , and thus perturb the checkpoint system responsible for anaphase onset.