Distribution of Receptors for Transferrin and Low Density Lipoprotein on the Surface of Giant HeLa Cells

Giant HeLa cells, having a spread diameter of about 200 micrometers, were briefly surface-labeled at 0 degree C with 125I-labeled transferrin, low density lipoprotein, anti-HeLa cell antibody, or concanavalin A. The cells were washed at 0 degree C, fixed, and autoradiographed. The distribution of grains when either anti-HeLa cell antibodies or concanavalin A was used was roughly as expected: the cell surfaces appeared uniformly labeled. When either transferrin or low density lipoprotein was used, about half the labeled cells had a nonuniform distribution of grains. On round cells, the cell periphery was more densely labeled than the middle of the cell; on elongated cells, cell protrusions were often more highly labeled than the rest of the cell. The simplest interpretation of these results is that, during their endocytic cycles through these cells, the transferrin and low density lipoprotein receptors are returned to the cell surface at the cell's leading edge.