Fluctuations spectrum of passive and active giant vesicles measured by contour analysis.

We have developed a new method of contour analysis using phase contrast microscopy on giant vesicles [1]. Our set-up allows an accurate detection at video rate, and a direct comparison with theory in a planar geometry. We have been able to measure directly fluctuations spectra. For pure lipid vesicles, we measure bending rigidities corresponding to those of the literature. Our technique has also been extended to non-equilibrium membranes. We have set up a protocol to prepare giant vesicles containing bacteriorhodopsine[2], a light- activated protons pump. When the protein is pumping this system is a simple model of active membrane. We have measured the fluctuation spectra of these active liposomes. As a first analysis, our results cannot be explained by actual active membranes theory [4] and are not in agreement with micropipette experiments [3-4].\\[4pt] [1] J.P\'{e}cr\'{e}aux et al. (2004) Eur. Phys. J. E 13(3): 277-290.\\[0pt] [2] P. Girard, J.P\'{e}cr\'{e}aux et al (2004), Biophys. J. 87: 419-429.\\[0pt] [3] J.-B. Manneville et al. (1999), Phys. Rev. Lett. 82: 4356-4359.\\[0pt] [4] J.-B. Manneville et al. (2001), Phys. Rev. E 64(2): 021908.