Prevention of chemically induced changes in synaptosomal membrane order by ganglioside GM1 and alpha-tocopherol

Synaptosomal membrane order has been studied by analysis of light depolarization by fluorescent dyes intercalated within membranes following exposure to various environmental toxicants. Two probes were explored: 1,6-diphenyl-1,3,5-hexatriene (DPH), signaling predominantly from the lipid-rich membrane core, and 1-[4-(trimethylamino)phenyl]-6-phenyl-1,3,5-hexatriene (TMA-DPH), reporting from the more hydrophilic membrane surface. Chlordecone, a neurotoxic insecticide, decreased the anisotropy of either dye and this change could be prevented by prior treatment of synaptosomes with ganglioside GM1 but not alpha-tocopherol. Exposure to an iron-ascorbic acid oxidizing mixture enhanced synaptosomal membrane order and this effect was blocked by preincubation with alpha-tocopherol but not ganglioside GM1. While these interactions may have partially reflected additive anisotropy changes, the protective agents were also effective at concentrations where they did not in themselves modulate membrane order. Methyl mercuric chloride at concentrations up to 100 microM had no discernable effect upon membrane order. It is suggested that these changes in membrane order may underlie some of the previously reported variations in the content of ionic calcium and in the leakiness of synaptosomes.