Fluorescence imaging of membrane dynamics in living cells.

Methods of wide-field fluorescence microscopy for measuring membrane dynamics of living cells are described, including spectral imaging as well as anisotropy imaging of the membrane marker 6-dodecanoyl-2-dimethylamino naphthalene (laurdan). Plasma membranes are selected by illumination with an evanescent electromagnetic field and distinguished from intracellular membranes assessed by whole-cell illumination. While fluorescence spectra of laurdan appeared red-shifted with decreasing membrane stiffness, fluorescence anisotropy and rotational correlation times were reduced with increasing membrane fluidity. Membrane stiffness was found to increase with decreasing temperature and increasing amounts of cholesterol and was always higher for the plasma membrane than for intracellular membranes. These effects may have some clinical relevance in the research of drug resistance or cell aging.