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  • Title: Dynamic imaging of lateral diffusion by electron spin resonance and study of rotational dynamics in model membranes. Effect of cholesterol.
    Author: Shin YK, Freed JH.
    Journal: Biophys J; 1989 Mar; 55(3):537-50. PubMed ID: 2539210.
    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.
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