Fig. 10. Phagosomes fuse at a higher rate in cells expressing RabD^Q67L, and this is dependent on PI 3-kinase activity. In A, control and RabD^Q67L cells incubated with or without the PI 3-kinase inhibitor, 20 µM LY294002 (Calbiochem), were pulsed for 10 minutes with FITC-bacteria in shaking suspension, washed and allowed to chase for 60 minutes in fresh HL-5 on coverslips. After a gentle fixation, phase contrast and fluorescent images were taken at 1000x magnification. The number of phagosomes within each cell and the number of bacteria within each phagosome were counted in a pool of at least 20 cells. A fusion event is defined as FE=n-1, where FE is a fusion event and n equals the number of bacteria within the phagosome. Differences in FEs between control and RabD^Q67L cells were very significant (P<0.0001). FEs between control and RabD^Q67L cells + LY294002 were not significantly different (P=0.2623). B depicts the comparison of fusion events between control and RabD^N121I-expressing cells in the same conditions described above. The difference in the number of fusion events between the two strains is significant (P=0.0232).