Cholesterol enrichment change HAS cell fusion kinetics. Changes in fluorescence intensity (F) were measured in the region of interest (ROI) near the center of HAS cells with a fixed area (35,904 pixel). HAS cells were enriched with cholesterol by standard incubation with soluble cholesterol-MβCD complex. (A, i–iii) Different kinetic phases are observed with CF transfer. (iv) Transfer of Alexa 10 kD dextran was initially slow, but then showed faster kinetics. In i–iv, time zero is the onset of dye diffusion. F measurement of an unfused cell pair is in v. (B) Time required to reach half-maximum fluorescence (n >7).