| Abstract: | Trypsinized guinea pig epidermal cells were separated by velocity sedimentation at unit gravity. Based on the relationship between cell size and both morphological and functional aspects of differentiation, the cells were classified as lower (a diameter <12.5 μM), middle (a diameter between 12.5 and 15 μM), and upper (a diameter >15 μM) epidermal cells. Fresh cells exposed to rhodaminated concanavalin A (Con A) were sedimented and reacted with fluoresceinated anti-Con A serum to distinguish cell surface Con A from intracellular lectin. Labeling at 4°C resulted in a uniform surface distribution of Con A irrespective of cell size. After a 1-hr incubation of Con A-labeled cells in lectin-free medium at 37°C, lower epidermal cells and approximately half of middle epidermal cells internalized Con A/receptor complexes by endocytosis while lectin remained diffusely on the remainder of middle epidermal cells and upper epidermal cells. By electron microscopy, ferritin-Con A was clustered on surface areas and invaginations of the plasma membrane before being endocytosed. We concluded that the differentiation of epidermal cells was accompanied by progressive decrease in endocytosis and, most probably, mobility of Con A receptors. |
