Diffusion-time distribution analysis (DDA) has been used to explore the plasma membrane fluidity of multidrug-resistant cancer cells (LR73 carcinoma cells) and also to characterize the influence of various membrane agents present in the extracellular medium. DDA is a recent single-molecule technique, based on fluorescence correlation spectroscopy (FCS), well suited to retrieve local organization of cell membrane. The method was conducted on a large number of living cells, which enabled us to get a detailed overview of plasma membrane microviscosity, and plasma membrane micro-organization, between the cells of the same line. Thus, we clearly reveal the higher heterogeneity of plasma membrane in multidrug-resistant cancer cells in comparison with the nonresistant ones (denoted sensitive cells). We also display distinct modifications related to a membrane fluidity modulator, benzyl alcohol, and two revertants of multidrug resistance, verapamil and cyclosporin-A. A relation between the distribution of the diffusion-time values and the modification of membrane lateral heterogeneities is proposed.
Fluorescence correlation spectroscopy (FCS) is a powerful experimental technique used to analyze the diffusion at the
single molecule level in solution. FCS is based on the temporal autocorrelation of fluorescent signal generated by dye
molecules diffusing through a small confocal volume. These measurements are mostly carried out in a chambered
coverglass, close to the glass substrate. In this report, we discuss how the chemical nature of the glass-water interface
may interact with the free diffusion of molecules. Our results reveal a strong influence, up to a few μm from the
interface, of the surface hydrophobicity degree. This influence is assessed through the relative weight of the two
dimension diffusion process observed at the vicinity of the surface.
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