Poster — Thur Eve — 38: The Effect of Ionizing Radiation on Giant Unilamellar Vesicles of “Lipid Raft” Mixtures Examined by Confocal Fluorescence Microscopy

The effect of ionizing radiation on model membranes has been the focus of various studies since the discovery of radioactivity. Spectroscopic techniques, such as X-ray diffraction, electron spin resonance, and fluorescence spectroscopy, yielded insight into radiation-induced physico-chemical changes in model membranes. However, direct visualization of the radiation-induced damage in model membrane systems was not possible before the advent of giant unilamellar vesicles. We describe a method of examining radiation-induced visible, physical changes in giant unilamellar vesicles consisting of a single bilayer, along with details of a possible reorganization of “lipid raft” domains. We used mixtures of phospholipids and cholesterol for which the phase behaviour is known and the contrast between the different lipid phases was achieved by using two well characterized fluorescent probes: Texas Red 1,2-dihexadecanoyl-sn-glycero-3-phosphoethanolamine (TR-DPPE), and 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine-N-(7-nitro-2-1,3-benzoxadiazol-4-yl) (NBD-DPPE). Samples were irradiated with a 137Cs gamma ray source at dose rates ranging from ∼0.3 Gy/min to ∼0.7 Gy/min and doses of 1 Gy to 30 Gy. The radiation-induced effects were examined at 15 minutes to ∼24 hours after irradiation, which is within the stability period of the giant unilamellar vesicles. We observed substantial aggregation of vesicles, and vesicles transitioned from a spherical to an elongated shape with bending points at the boundaries of “lipid raft” domains. Although giant unilamellar vesicles do not contain genetic material, it seems likely that by incorporating membrane proteins, questions pertaining to different cellular processes such as signal transduction and apoptosis induced by radiation could be addressed.