Surface membrane traffic in guinea pig basophils exposed to cationic ferritin

Surface membrane traffic patterns can be influenced by a number of factors, including the functional state of the cell. We used transmission electron microscopy to investigate the fate of surface membrane in guinea pig basophils exposed to cationized ferritin (CF) in vitro. CF bound to the plasma membrane and was internalized on the membranes of vesicles and vacuoles, a process that was particularly prominent at the uropod of basophils exhibiting a polarized ('motile') configuration. The vesicles/vacuoles moved to the Golgi area, or, in the case of degranulating basophils, were observed in continuity with the degranulation sac, a structure formed largely by the fusion of individual cytoplasmic granule membranes. However, CF-positive vesicles were never observed to fuse directly with the membranes of intact cytoplasmic granules.