Effect of ultra-violet radiation on the liposomal membrane

Characterization of the UV-induced electrophysiological response in smooth muscle

The effect of ultraviolet (UV) light on taenia caeci smooth muscle of guinea-pig was studied. This stimulus induced a decrease in membrane conductance, hyperpolarization of the smooth muscle cells, a decrease in spike activity and a diminished level of cGMP and enhancement of lipid peroxidation. The hyperpolarization evoked by UV light was attenuated in the presence of sodium nitrite, reaching a maximum at 0.5 mM sodium nitrite. The level of cGMP was enhanced in the presence of nitrite and lipid peroxidation was not changed. Under these conditions lipid peroxidation was not changed during UV irradiation either. The UV-induced hyperpolarization was abolished in the absence of extracellular calcium, inhibited in the presence of 8-Br-cGMP and enhanced by an increase in the extracellular calcium concentration. These results are consistent with the supposition that UV-A irradiation blocks calcium influx via a cGMP-dependent mechanism.

Interaction of cytochrome c with liposomes: covalent labeling of externally bound protein by the fluorescent probe, azidonaphthalenedisulfonic acid, enclosed in the inner aqueous compartment of unilamellar vesicles

The photoreactive fluorescent probe, 3-azidonaphthalene-2,7-disulfonic acid (ANDS) was encapsulated in the inner aqueous compartment of small unilamellar liposomes, prepared from egg phosphatidylcholine (PC) +/- 20 mol% dihexadecylphosphate (DHP). After adding cytochrome c externally to a suspension of these vesicles, the probe was activated by ultraviolet irradiation, and the protein was separated from the lipids. When negatively charged (egg PC/DHP) vesicles at low ionic strength were used, which form an electrostatic complex with cytochrome c, the protein was labeled by ANDS. This process depended on irradiation time, and was inhibited by increasing the ionic strength of the medium. Labeling was not observed with isoelectric (egg PC) vesicles. These observations suggest that electrostatic binding of cytochrome c to the bilayer is accompanied by intramembrane penetration to such a depth that the protein can communicate with the inner membrane-water interface.

Liposomes as membrane model for study of lipid peroxidation

This article describes the properties, production and characterization of liposomes with special reference to their use as membrane model for the study of lipid peroxidation. It presents briefly the methods that can be used for the assay of liposomal lipid peroxidation and brings out the special advantages these liposomes provide in elucidating the mechanism of lipid peroxidation by different physical and chemical agents. Studies involving liposomal lipid peroxidation by different agents and the consequent changes in the structure and function of liposomal membrane have been reviewed briefly.

Localization of lipid peroxidation products in liposomes after gamma-irradiation

The distribution of lipid peroxidation products in liposomes after gamma-irradiation at various doses was studied. Increases in thiobarbituric-acid-reactive substances, in the absorbance at 232 nm and in hydroperoxides were observed mainly in liposomal membranes after relatively low doses of irradiation, while carbonyl compounds were distributed both inside and outside the membranes. After higher doses of irradiation, however, the absorbance at 232 nm and the amount of hydroperoxides reached a maximal level in the membrane portion and then decreased when the decomposition products were released from the membranes. Under this condition, malondialdehyde and other carbonyl compounds were increased mainly in the medium of liposomal suspension. These results are discussed with reference to the lipid peroxidation process which is induced quantitatively by ionizing radiation.