Micro-organisation of the membrane after radiation-induced apoptosis: a flow cytometry study

The aim of this study was to detect membrane fluidity modifications in bloo d lymphocytes that had been exposed to gamma -radiation, at a graded series of depths from the surface to the centre of the membrane bilayer and as a function of cell viability. A time course was performed to verify the contr ibution of the membrane to radiation-induced apoptosis. In comparison with spectrofluorimetry, flow cytometry proved to be a reliable method for measu ring radiation-induced membrane alterations. Late apoptotic lymphocytes wer e characterised by a significant decrease of the 3-SA, 6-SA and 9-SA fluore scence anisotropy values, compared to viable lymphocytes. Moreover, a highl y significant difference was observed in the early apoptotic lymphocyte sub population between the fluorescence anisotropy values measured 24 h (radiat ion-induced apoptosis) and those measured 1 h (spontaneous apoptosis) after irradiation. The simultaneous assessment of cellular viability and membran e fluidity using n-(9-anthroyloxy) fatty acid probes, may be relevant for t he investigation of interactions which may exist between membrane modificat ions and the apoptotic process. Our observations support the specificity of radiation-induced apoptosis compared to spontaneous apoptosis in terms of biophysical modifications of membrane properties.