ABSTRACT
Plasma Membrane ............................................................................ 432 19.1.2 Plasma Membrane Lipids ................................................................. 433 19.1.3 Lipid-Induced Nanodomains ............................................................ 433 19.1.4 Cortical Cytoskeleton ....................................................................... 434
19.2 Detection of Membrane Heterogeneity by Optical MicroscopyLimitations .................................................................................................... 434 19.2.1 Imaging-Temporal Resolution ........................................................ 435 19.2.2 Single-Molecule Tracking ................................................................ 435 19.2.3 Fluorescence Correlation Spectroscopy ........................................... 436 19.2.4 Optical Microscopy-The Spatial Resolution Limit ........................ 436 19.2.5 Far-Field Optical Nanoscopy ............................................................ 437
19.3 STED-FCS .................................................................................................... 438 19.3.1 Reduced Observation Spot: The Concentration Issue ...................... 438 19.3.2 Tuning of the Observation Spot: Studying Molecular Interactions .... 439
19.4 Studying Lipid-Membrane Dynamics Using STED-FCS ........................... 441 19.4.1 Live-Cell Lipid Plasma Membrane Dynamics: Phospholipid
versus Sphingolipid Diffusion .......................................................... 441 19.4.2 Live-Cell Lipid Plasma Membrane Dynamics: Possible Artifacts .....442 19.4.3 Live-Cell Lipid Plasma Membrane Dynamics: Molecular
Dependencies ....................................................................................442
The cellular plasma membrane is built up by a lipid bilayer and contains a multitude of different lipids and proteins, which among other things play a central role in cellular signaling (Figure 19.1). It is well acknowledged that the different membrane molecules are highly dynamic but do not just simply diffuse freely as introduced in 1972 by the “uid mosaic model.”1 Rather, molecular membrane diffusion is usually restricted and hindered; that is, it shows highly anomalous diffusion patterns and
