| Abstract: | The internalization of membrane markers during phagocytosis was followed in guinea pig granulocytes as a function of the extent of particle ingestion. The plasmalemma was carefully labeled with diazotized 35S-sulfanilate, or by treatment with periodate and sodium 3H-borohydride. These treatments provided general membrane markers. More specific markers used were 5′-nucleotidase, neuraminidase-releasable membrane sialate, and concanavalin A binding sites. In all cases except the last, internalization of membrane was directly determined on isolated phagosomes; disappearance of binding sites from the cell surface was followed in the last instance. Both phagosomal levels and disappearance from the surface were measured in the case of 5′-nucleotidase, permitting balance studies. Phagocytosis was determined as uptake of paraffin emulsions labeled with Oil-Red 0. “Marker/particle” ratios were determined as the percent external marker internalized per mg paraffin ingested. The “marker/particle” ratios for cells with chemically labeled membranes were considered to reflect random internalization of membrane entities. Colchicine had no effect on those ratios. Internalization of 5′-nucleotidase and neuraminidase-releasable sialate gave “marker/particle” ratios similar to those of the random markers, and these increased in the presence of colchicine. Concanavalin A binding sites did not appear to be removed from the cell surface in the absence of colchicine, but disappearance was observed in its presence. Control experiments indicated that these changes due to colchicine must be very cautiously interpreted. Our results differ from those obtained by others, and the reasons due to species, cell type, experimental design, etc. are discussed. Maximal particle uptake was computed to require internalization of one-fifth to one-third of the total external membrane of the cells—based on the assumption of random internalization of markers. |
