Recent findings suggest that membrane vesicle transport during mitosis may be generally inhibited. To test this, we examined the kinetics of uptake and exocytosis of RITC-transferrin in mitotic and interphase HeLa cells. We used quantitative image-intensification fluorescence microscopy to analyze the content of ligands in single cells. This technique was validated by comparison of 3H or RITC-transferrin release from interphase cells determined by microscopy or radiometry. Both methods gave a t1/2 of release of 5-6 min. The uptake of RITC-transferrin was depressed in mitotics. More importantly, we monitored the exocytosis of label during mitosis. Labeled mitotics were obtained by the progression of interphase cells into mitosis during a 50 min incubation with RITC-transferrin. After 30 min chase with unlabeled transferrin, the intensities of interphase cells approached background, whereas those of mitotic cells remained nearly constant. Thus both exocytosis and endocytosis of transferrin were exocytosis and endocytosis of transferrin were blocked during mitosis.

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