MEMBRANE FLUIDITY OF MICROSOMAL AND THYMOCYTE MEMBRANES AFTER X-RAY AND UV IRRADIATION

A brief literature review shows that ionizing radiation in biological membranes and in pure lipid membranes causes malondialdehyde formation , indicating lipid peroxidation processes. With respect to membrane fl uidization by ionizing radiation, in pure lipid membranes rigidization effects are always reported, whereas contradictory results exist for biological membranes. Starting from the assumption that membrane prote ins at least partly compensate for radiation effects leading to a rigi dization of membrane lipid regions, pig liver microsomes, as a represe ntative protein-rich intracellular membrane system, were irradiated wi th X-rays or UV-C with doses up to 120 Gy at a dose rate of 0.67 Gy mi n(-1) and up to 0.73 J cm(-2) at an exposure rate of 16.2 mJ cm(-2) mi n(-1), respectively. For both irradiation types a weak but significant positive correlation between malondialdehyde formation and membrane f luidity is revealed throughout the applied dose ranges. We conclude th at the membraneous protein lipid interface increases its fluidity unde r radiation conditions. Also, thymocyte ghosts showed an increased flu idity after X-ray irradiation. Fluidity measurements were performed by the pyrene excimer method.