Fig. 2. Intracellular fusion of vesicles containing internalized anti-PRL. Quantitative fluorescence analysis of data from experiments described in Fig. 1 suggest fusion of the structures containing the internalized anti-PRL. Analysis was performed on complete z-series of images as described in Materials and Methods. (A) The number of structures containing internalized anti-PRL decreased over time. The graph shows the mean (±s.e.m.) number of stained puncta per cell at each time point. The difference between the means at t=0 (100.6±7.0) and t=20 (38.6±4.3) and between t=0 and t=80 (42.0±5.0) were significant (P<0.005; Student's t-test). (B). Relative size of the structures containing internalized anti-PRL over time was estimated from the fluorescence intensity of individual puncta. Histograms of the integrated fluorescence of individual puncta in cells at each time point demonstrate a clear increase in the proportion of brightly stained (large) structures at the 20 and 80 minute time points compared to the 0 time point (means were significantly different; P<0.001; Mann-Whitney U-test). Data are pooled from 10-12 randomly selected cells per time point.