Abstract
Steady-state fluorescence polarization of the fluorescent probe 1,6-diphenyl-1,3,5-hexatriene reported temperature-dependent lipid order in l-α-dimyristoylphosphatidylcholine, egg phosphatidylcholine and synaptosomal membranes. No change in lipid order was detected after depolarization of synaptosomes by veratridine (150 μM) even in the presence of 2 mM CaCl 2. However, Ca 2+ reduced the mobility of a second probe, dansylated dipalmitoylphosphatidylethanolamine, in dispersions of synaptosomal lipids. This effect, which was seen at a Ca 2+/total phospholipid ratio as low as 0.1, may represent an interaction between the cation and negatively-charged phospholipids. It is suggested that Ca 2+ promotes a phase separation in synaptosomal lipids which may be relevant to the process of neurotransmitter release.
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