DIRECT ENDOCYTOSIS OF CONCANAVALIN-A BY MOTILE FIBROBLASTS

The distribution of total and cell surface concanavalin A (ConA) in the motile cell lines, BHK21 and L929, was established by direct and indirect immunofluorescence. Exposure of BHK21 and L929 cells to ConA results in the direct endocytosis of lectin in the absence of any global surface redistribution. The kinetics of lectin internalization observed by fluorescence microscopy are strikingly similar in the two motile cell lines and a third, non-motile cell line, CHO. Direct lectin interiorization was observed over a wide range of ConA concentrations and experimental conditions including chases in lectin-free medium. At high ConA concentrations, cell surface clearing of lectin from ruffle-like areas at the cell margin occurred. Treatment of cells with the antimitotic agent, colcemid, had little effect on the direct pinocytosis of lectin. Cytochalasin B (CB) treatment inhibited lectin endocytosis and produced scattered minicaps of ConA about the cell surface. The dominance of direct endocytosis of bound lectin over redistribution in the plane of the membrane may be maintained by the localized organizational state of microfilaments. © 1978.