title: The effects of Ca2+ on lipid diffusion.
abstract: The effects of Ca2+ on rotational and translational diffusion of lipids in multilamellar dimyristoylphosphatidylcholine (DMPC)-water systems were investigated by time-resolved phosphorescence anisotropy steady-state fluorescence polarization and fluorescence recovery after photobleaching (FRAP) experiments. Above the phase transition temperature (Tm), addition of Ca2+ caused a steady increase in the segmental motion of the phosphorescent probe, but resulted in slower diffusion of the fluorescent and lateral diffusion probes. The former result is attributed to changes in the structure of the lipid/water interface that affects the chromophore mobility on the phosphorescence time scale but does not reflect lipid motion. Below the phase transition temperature, slower diffusion of all probes were observed with increasing concentrations of Ca2+, with sudden large changes occurring at [Ca2+] approximately 500 mM. This behaviour is attributed to association of Ca2+ with the lipid phosphate groups and the exclusion of water molecules which results in tighter packing of lipids and smaller segmental motion, leading eventually to the immobilization of lipid molecules.
mesh_terms: D002118:Calcium; D004058:Diffusion; D004134:Dimyristoylphosphatidylcholine; D007700:Kinetics; D008081:Liposomes; D008163:Luminescent Measurements; D008954:Models, Biological; D013050:Spectrometry, Fluorescence
chemical_list: D008081:Liposomes; D002118:Calcium; D004134:Dimyristoylphosphatidylcholine