The intracellular movement of endocytic vesicles in cultured granulosa cells

Ligand binding to cell surface receptors induces rapid internalization of ligandreceptor complexes by receptor mediated endocytosis. We have examined the intracellular movement of endocytic vesicles, induced by the lectin concanavalin A (Con A), in cultured rat ovarian granulosa cells using fluorescence and electron microscopy. Within 20 minutes of ligand treatment at 37°C, numerous Con A‐containing endocytic vesicles form, which migrate to the cell center by 60 minutes. Double label fluorescence microscopy, using fluorescien‐Con‐A and rhodamine immunofluorescent staining of tubulin or vimentin, indicates that during vesicle migration microtubules and 10‐nm filaments are altered in their organization. By 30 minutes, vesicles are associated with microtubule bundles, which subsequently collapse around the nucleus. Similarly, 10‐nm filaments accumulate around the nucleus in conjunction with the perinuclear aggregation of endocytic vesicles. Electron microscopy of Con A‐horseradish peroxidase‐labeled cells demonstrates that endocytic vesicles fuse to form large receptosome‐like structures during intracellular migration and these structures are associated with cytoplasmic microtubules and 10‐nm filaments. Taxol, a drug that stabilizes microtubules, prevents endocytic vesicle translocation to the Golgi region. Nocodazole, which causes microtubule disassembly, results in the collapse of 10‐nm filaments and the central aggregation of endocytic vesicles. The data indicate that the cytoskeleton participates in the directed intracellular movement of endocytic vesicles; the possible subcellular basis for this movement is discussed.