title: Dynamic imaging of lateral diffusion by electron spin resonance and study of rotational dynamics in model membranes. Effect of cholesterol.
abstract: The effects of cholesterol on the dynamics and the structural properties of two different spin probes, the sterol type CSL and the phospholipid type 16-PC, in POPC/cholesterol oriented multilayer model membranes were examined. Our results are consistent with a nonideal solution containing cholesterol-rich clusters created by the self association of cholesterol in POPC model membranes. The lateral diffusion coefficient D of the spin probes was measured over the temperature range of 15 to 60 degrees C and over the concentration range of 0 to 30 mol% of cholesterol in the model membrane by the electron spin resonance (ESR) imaging method. The rotational diffusion coefficients (including R perpendicular) and the order parameter S were determined utilizing a nonlinear least square ESR spectral simulation method. D, R perpendicular and S of CSL deviate considerably from linear dependence on mole percent cholesterol. The D of CSL was decreased by a factor of four at 15 degrees C and a factor of two at 60 degrees C for concentrations of cholesterol over 10 mol %, whereas those of 16-PC were hardly affected. Cholesterol decreased R perpendicular by a factor of 10 at 30 mol % of cholesterol, but it increased slightly that of 16-PC. A significant increase of S for CSL due to the presence of cholesterol was observed. It is shown how the difference in variation of S for CSL vs. 16-PC with composition may be interpreted in terms of their respective activity coefficients, and how a single universal linear relation is obtained for the S of both probes in terms of a scaled temperature. Simple but general correlations of D and of R perpendicular with S were also found, which aid in the interpretation of these diffusion coefficients.
authors.affiliation: Baker Laboratory of Chemistry, Cornell University, Ithaca, New York 14853.
authors.forename: Y K
authors.initials: YK
authors.lastname: Shin
authors.forename: J H
authors.initials: JH
authors.lastname: Freed
mesh_terms: D002784:Cholesterol; D004058:Diffusion; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods; D008081:Liposomes; D008433:Mathematics; D008962:Models, Theoretical; D010713:Phosphatidylcholines; D012399:Rotation; D013113:Spin Labels
chemical_list: D008081:Liposomes; D010713:Phosphatidylcholines; D013113:Spin Labels; D002784:Cholesterol; C028694:1-palmitoyl-2-oleoylphosphatidylcholine