<p> Measuring the elasticity of membrane domains in living cells</p><p>Frank Lafont</p><p>Institut Pasteur de Lille, Microbiologie cellulaire et pathogénie infectieuse, Institut de Biologie de Lille CNRS UMR8161 1 rue du Prof Calmette , 59021 Lille, France Email : [email protected] WWW : http://www.pasteur-lille.fr/fr/recherche/unites/umr8161lafont_mars.html WWW : http://www.ibl.fr/mcpi</p><p>Physiopathological disorders often occur from uncoupling external signals and the transduction cascade subsequently triggered. Alternatively, many infectious invading microorganisms hijack cell surface binding sites either subverting receptors or by mimicry of natural ligands. The plasma membrane is now considered as a heterogeneous system with lipids and proteins partitioning within confinement microdomains the dynamics of which varies in function of the activation status of the cell. Biochemical and imaging methods have been used to characterize the composition and viscosity of these domains as well as the diffusion rate of proteins and lipids that experience time residency within these domains. Atomic Force Microscopy (AFM) offers high resolution to study interaction forces and sample stiffness and can be used in liquid. It is possible to analyze on one scanning frame the topology of the sample, the distribution of cell surface binding sites and the elasticity of the sample. The molecular heterogeneity of membrane domains induces heterogeneity in their biophysical properties. Among these, mechanical properties, which are crucial for bacterial adhesion for instance, can be accessible to AFM examination. Using functionalized tips to target specifically membrane proteins, it is then possible to measure the elasticity the membrane domain-containing these proteins 1 . AFM also allows addressing some membrane trafficking issues as for instance the time exposure of membrane proteins at the cell surface 2 . Hence, it becomes obvious that AFM is entering as a new powerful technique in the toolbox of cell biologists. Moreover, by combining biophotonic imaging techniques with AFM, it will be soon possible to target at the single molecule level and nanometrical scale both cellular distribution, interaction forces and local biophysical features. We will discuss these new approaches that are currently emerging.</p><p>1) Elastic membrane heterogeneity of living cells revealed by stiff nanoscale membrane domains. Biophys. J., 2008, 94, 1521-1532 C. Roduit, F.G. van der Goot, P. De Los Rios, A. Yersin, P. Steiner, G. Dietler, S. Catsicas, F. Lafont* and S. Kasas*.</p><p>2) Elastic properties of the cell surface and trafficking of single AMPA receptors in living primary hippocampal neurons. Biophys. J., 207, 92, 4482-4489 A. Yersin, H. Hirling, S. Kasas, C. Roduit, K. Kulangara, G. Dietler, F. Lafont, S. Catsicas, P. Steiner</p>