Figure 3.

(a(i)) Proposition 8: liquid ordered and liquid disordered phases coexist in the plasma membrane. Laurdan is a lipophilic dye that changes fluorescence emission upon contact with water molecules; it is frequently used to probe the lipid packing and thereby the membrane order. (a(ii)) Single diffusing Laurdan dyes change their emission from red to blue when they diffuse from liquid disordered to an ordered phase. (b(i)) Proposition 9: different membrane proteins are associated and form so-called protein islands; the proteins are trapped within islands for at least 4–10 s. (b(ii)) PALM relies on the repeated switching and localization of photo-activatable fluorophores. A minute fraction of inactive fluorophores is activated by illumination with a short wavelength. The active fluorophores are imaged at single-molecule level, and photobleached. Activation, imaging and photobleaching are repeated until most fluorophores have been recorded. On the individual frames, the single dye molecules can be localized with a precision of approximately 20 nm; all positions yield the final high-resolution image. (c) Proposition 10: SMT and SPT can be used to measure the influence of cortical actin on the diffusion of membrane proteins. For actin-associated diffusion, the tracked particles show a one-dimensional diffusion along the underlying actin fibres (e.g. CD36), for other proteins (e.g. the Fcε-receptor) free diffusion in the voids of the actin meshwork was observed.