Differences of cell surface label distribution and redistribution patterns between mammalian keratinocytes and melanocytes in culture.

Primary guinea pig epidermal cell cultures were subjected to a variety of ultrastructural surface labeling techniques specific for lectin binding sites (Concanavalin A-horseradish peroxidase, wheatgerm agglutinin-chitobiosyl-horseradish peroxidase) or anionic surface sites (Ruthenium red, cationized ferritin). All these techniques were carried out on fixed cells; with cationized ferritin, labeling was also performed on unfixed, viable cells by incubation at 4 degrees C and 37 degrees C for various time periods. Lectin labeling resulted in a diffuse pattern identical for both melanocytes and keratinocytes. Different patterns were obtained with the markers for anionic sites: with both ruthenium red and cationized ferritin, fixed keratinocytes were more heavily labeled than melanocytes, the label being diffuse with randomly distributed globular condensations. Melanocytes, in contrast, were lined by a thin uniform band-like label. On viable keratinocytes, exposed to cationized ferritin at 4 degrees C, the label was confined to randomly disseminated patches which most probably represent the "inherent" distribution of anionic surface sites. At 37 degrees C, this pattern was progressively changed by cluster formation as expression of ligand induced label redistribution, shedding and endocytosis of label material. In contrast, viable melanocytes lacked all of these activities except endocytosis, invariably displaying the same uniform diffuse labeling pattern as fixed melanocytes. It is concluded that melanocytes differ from keratinocytes with regard to quantity, distribution, and lateral mobility of anionic surface sites whereas no differences pertain to quantity and distribution of the binding sites to the lectins tested.