Figure 3.

Effect of solution viscosity on the diffusion of the protein and the lipid (in the absence of actin). The viscosity of the solution was varied using different concentrations of sucrose. (A) Diffusion coefficients were determined by LSFCS, because compared to point FCS this method is less susceptible to distortions of the focal volume due to the use of a solution with a refractive index deviating from that of water. A line was continuously scanned and the spatio-temporal correlation in a free-standing part (indicated by the two strokes) was computed and fitted with a model function for 2D diffusion. Scale bar 5 μm. (B) Increase in focal waist depending on the viscosity of the buffer as determined by LSFCS. (C) Absolute changes in the lateral diffusion D of the labeled lipid (circle) and the protein (square). The mobility of both probes decreases with increasing viscosity. (D) Plotting the relative changes in mobility shows that, in contrast to the experiments in the presence of actin, the diffusion of both probes is affected to a comparable extent. The diffusion coefficients were normalized to the respective diffusion coefficient at 0% sucrose. All error bars are standard deviations.