A fluorescence polarization study of calcium and phase behaviour in synaptosomal lipids.
Steady-state fluorescence polarization of the fluorescent probe 1,6-diphenyl-1,3,5-hexatriene reported temperature-dependent lipid order in L-alpha-dimyristoylphosphatidylcholine, egg phosphatidylcholine and synaptosomal membranes. No change in lipid order was detected after depolarization of synaptosomes by veratridine (150 microM) even in the presence of 2 mM CaCl2. However, Ca2+ reduced the mobility of a second probe, dansylated dipalmitoylphosphatidylethanolamine, in dispersions of synaptosomal lipids. This effect, which was seen at a Ca2+/total phospholipid ratio as low as 0.1, may represent an interaction between the cation and negatively-charged phospholipids. It is suggested that Ca2+ promotes a phase separation in synaptosomal lipids which may be relevant to the process of neurotransmitter release.
D000818:Animals; D001921:Brain / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D004161:Diphenylhexatriene / Q000378:metabolism; D005454:Fluorescence Polarization; D006168:Guinea Pigs; D008433:Mathematics; D013574:Synaptosomes / Q000378:metabolism*
D004161:Diphenylhexatriene; D002118:Calcium