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  Physics Express 2014, 4: 6
  Research Article
X-ray diffraction and confocal fluorescence microscopy studies on the effect of cholesterol on phospholipid membranes
  Sanat Karmakara, V. A. Raghunathanb  
a Department of Physics, Jadavpur University, 188 Raja S. C. mallick Road, Kolkata, 700 032, India
b Raman Research Institute, Shadashivanagar, Bangaluru, 5600 80, India

  We have studied the influence of cholesterol on the bilayer properties of phospholipid membranes using small angle x-ray scattering and laser scanning confocal fluorescence microscopy. We have obtained a cholesterol induced modulated (Pβ) phase in oriented multilayers of dipalmitoyl phosphatidylcholine (DPPC)-cholesterol mixtures at 98% relative humidity at intermediate cholesterol concentrations. The Pβ phase, which is distinct from the usual ripple (Pβ') phase, is absent in unoriented samples in excess water. However, we observe enhanced swelling of the bilayers in this part the phase diagram. This results is also supported by the fact that giant unilamellar vesicles (GUVs) at small cholesterol concentration (< 10 mol%) show significant shape fluctuations, indicating softening of bilayers in the presence of cholesterol. However, interestingly smaller GUVs (diameter < 20 µm) are almost spherical in shape and show dark irregular domains on a bright background, indicating the coexistence of gel and fluid phases.
  Model membrane; Small angle x-ray diffraction; Fluorescence microscopy  

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