Vesicle mobility and membrane flow are downregulated under hypertonic conditions. Cells were either labeled with TRITC-Dextran (A) or with Cy3.5 (B). Points of time at which confocal images were scanned are indicated in seconds referring to the onset of hyperosmotic shock as T = 0. (A) The fluorescent label of TRITC-Dextran in red is superimposed to phase contrast images in blue. TRITC-Dextran labeled vesicles of cells suspended in SPB buffer are mobile (indicated by arrows in frames -120, -60). Upon sorbitol shock, perturbation and immobilization of vesicles was observed. As an example, a region with stalled and distorted vesicles is indicated by arrows in frames 60-300. (B) The fluorescent label of Cy3.5 in red is superimposed to phase contrast images in blue. Cells suspended in SPB buffer occassionally endocytose membrane (arrows in frames -120, -60). Upon hyperosmotic shock, the plasma membrane thickens and forms spikes after cell shrinkage. The spikes are not endocytosed but remain fixed. Typical spikes are indicated with arrows in frames 30-300. Bar = 2 μm.